AI Instructions

## Data access: ARX.SDK

This project uses ARX.SDK 1.0.0-rc.1 with PostgreSQL (package `ARX.SDK.PostgreSql`, service `ArxPgDbService`).

- Use the `arx-sdk` skill for any code that reads or writes the database. Its references for this provider are in
  `.claude/skills/arx-sdk/references/postgresql/`: read `arx-postgresql-guide.md` and `arx-postgresql-types.md` first.
- Use only the ARX types and members listed in `arx-postgresql-types.md`. If something isn't there, say ARX doesn't
  offer it; don't invent a name.
- Start from the closest verified sample in the operation's file (`arx-postgresql-create.md` and the others).
- After changing ARX code: `dotnet build`, run the tests, and check every ARX call against the types file.
- When the ARX.SDK package version changes, download the skill again and update the version above.

## Data access: ARX.SDK

This project uses ARX.SDK 1.0.0-rc.1 with PostgreSQL (package `ARX.SDK.PostgreSql`, service `ArxPgDbService`). Its knowledge
files, generated from the library and its verified samples, are in `docs/arx-sdk/references/postgresql/`; the files named
below are there. Read `arx-postgresql-guide.md` and `arx-postgresql-types.md` before writing data access code,
and the operation's file (`arx-postgresql-create.md`, `-create-multiple.md`, `-update.md`, `-update-multiple.md`,
`-delete.md`, `-delete-multiple.md`, `-retrieve.md`, `-retrieve-multiple.md`, `-execute.md`) for its samples.

You help a developer write C# code that uses ARX.SDK with PostgreSQL (package `ARX.SDK.PostgreSql`). Follow these
rules.

1. **Use ARX's types for database work.** Create, update, delete and read rows, call procedures and functions, and run
   transactions through `ArxPgDbService`, `ArxPgConnection` and `ArxTransaction`. Don't write Npgsql code
   (`NpgsqlConnection`, `NpgsqlCommand`) or SQL text for work ARX does.
2. **Don't invent API.** Use only the types, methods, properties and parameters listed in `arx-postgresql-types.md`. If
   something isn't there, say ARX doesn't offer it rather than guessing a name.
3. **A row is an `ArxEntity`.** `var account = new ArxEntity("account");` then values by column name:
   `account["name"] = "Northwind Traders";`. Table and column names are the database's, as strings.
4. **Declare every table's id column once, at startup,** in an `ArxSchemaCatalog`, and give it to the service:
   `ArxSchemaCatalog.Create().Table("account", ArxIdColumn.Generated<long>("id")).Build()`, then
   `new ArxPgDbService(connectionString, schema)`. Use `ArxIdColumn.Supplied<string>("code")` for an id the application
   provides and `ArxIdColumn.NoIdColumn` for a table without one; add business keys with
   `.Key("account", "account_number")`. ARX never guesses an id: an undeclared table is ARX1016. ARX never creates or changes tables: the application's scripts or migrations do, so when the user has no table yet, give its CREATE TABLE too ("Your first table" in the Using your own tables guide has one per database). A service created
   without a catalog (`new ArxPgDbService(connectionString)`) reads each table's primary key and column types from the
   database before every call instead: much slower, only for simple CRUD in small applications (set
   `RememberResolvedTables = true` to read each table once); a table without a usable primary key is then ARX1019. Reads through such a service don't know the id: rows read back have `RecordId` null and lookups come back as their plain ids, so read the id column itself (`row["book_id"]`) or give the service a catalog.
5. **Every call is asynchronous** (`CreateAsync`, `CreateMultipleAsync`, `UpdateAsync`, `UpdateMultipleAsync`,
   `DeleteAsync`, `DeleteMultipleAsync`, `RetrieveAsync`, `RetrieveMultipleAsync`, `ExecuteAsync`); await it, and pass
   the caller's `CancellationToken` where the method takes one.
6. **Create returns the id.** `ArxRecordId id = await service.CreateAsync(entity);` (also set on `entity.RecordId`);
   `CreateMultipleAsync` returns one id per entity, in list order. Point a lookup column at another record with
   `new ArxEntityReference("account", id)`.
7. **Update and Delete find rows by the id, a declared key, or columns you name:**
   `new ArxUpdateOptions { Match = ArxMatch.Key("account_number") }`, `ArxMatch.Columns(...)`. An update changes only
   the attributes that are set; setting one to `null` clears that column.
   **To change or delete every row a condition matches** (from 0.1.0-preview.5): an entity with only the values to set
   and an `ArxFilterExpression`, `int changed = await service.UpdateMultipleAsync(values, filter);`, or
   `await service.DeleteMultipleAsync("account", filter)`; one statement (binary `COPY` for a create of 5,000 rows or more of one shape), all or nothing, returning the count. The
   entity carries no id (ARX1001 with a filter); an empty filter is ARX1001 unless
   `new ArxFilterWriteOptions { AllRows = true }`. For a large insert whose ids aren't needed:
   `CreateMultipleAsync(entities, new ArxCreateMultipleOptions { ReturnIds = false })` (every id `ArxRecordId.None`).
8. **Reads.** `RetrieveAsync` returns `null` when nothing matches. `RetrieveMultipleAsync` takes an
   `ArxQueryExpression` (criteria, columns, order, paging, links to other tables) and returns the rows in `.Entities`.
   **Query cheat sheet** (the exact names; there are no others, such as `AddGroupBy` or `MoreRecords`):
   `var query = new ArxQueryExpression("book");` · columns: `query.ColumnSet = new ArxColumnSet("title", "year");`
   (empty: every column) · conditions: `query.Criteria.AddCondition("year", ArxConditionOperator.Between, 2000, 2010);`
   (Equal, NotEqual, GreaterThan, GreaterEqual, LessThan, LessEqual, Between, In, NotIn, Like, Contains, BeginsWith,
   EndsWith, Null, NotNull and their Not/DoesNot forms) · an OR group: `var either = query.Criteria.AddFilter(ArxLogicalOperator.Or);`
   then `either.AddCondition(…)` · order: `query.AddOrder("title", ArxOrderType.Ascending);`
   · a join: `var author = query.AddLink("author", "author_id", "id", ArxJoinOperator.Inner); author.EntityAlias = "a";
   author.ColumnSet = new ArxColumnSet("name");`, read as `row["a.name"]` · paging:
   `query.PageInfo = new ArxPagingInfo { Count = 20, PageNumber = 1, ReturnTotalRecordCount = true };`, then
   `result.Entities`, `result.HasNextPage`, `result.TotalRecordCount` · grouped counts:
   `query.AggregateInfo = new ArxAggregateInfo(); query.AggregateInfo.AddAggregateColumn("books", "id", ArxAggregateOperator.Count);
   query.AggregateInfo.AddGroupByColumn("author_id");` (Count reads back as a `long`). A foreign key column reads back as
   an `ArxEntityReference` (with the referenced row's name) only when the catalog declares it:
   `.Lookup("book", "author_id", "author")` and `.DisplayName("author", "name")`; otherwise it is the plain id.
9. **Values are always parameters:** pass them as .NET values and never build SQL with them. A table or column name
   that carries SQL is refused with ARX1017, but a valid name is used as given: a name typed by a user can read any
   table or column the database user can (`pg_catalog.pg_roles`, `information_schema.columns`). Never pass a name from a user unchecked: map it to one the
   application allows (an allow list), or preload the schema and set `Strict = true`.
10. **Dates:** `DateTimeOffset` or a UTC `DateTime` for a moment (`timestamptz`), a `DateTime` with Kind `Unspecified`
    for a wall-clock time (`timestamp`), `DateOnly`, `TimeOnly`, `TimeSpan` (`interval`). Never `default(DateTime)`
    (ARX1013: use `null`) and never a date as a string (ARX4004).
11. **Errors** are `ArxException`s with a stable `Code`: catch by code
    (`catch (ArxException error) when (error.Code == ArxErrorCode.UniqueViolation)`: catch the base class, since the class tells where an error was found and the code what happened) and retry only when
    `error.IsTransient` is true. `arx-postgresql-error-codes.md` lists every code.
12. **Transactions:** `await using var connection = new ArxPgConnection(connectionString);`,
    `await using var transaction = await connection.BeginTransactionAsync();`, pass `transaction` to each call, then
    `await transaction.CommitAsync();`. Disposing without committing rolls back. Code written against `IArxDataService` opens one without the provider type: `await using var transaction = await service.BeginTransactionAsync();` (from 0.1.0-preview.5; the transaction owns its connection). For many calls as one unit,
    `await service.RunBatchAsync(async batch => { … });` commits when the body returns.
13. **Base answers on the samples** in the operation files: they are verified code. Say which sample a pattern comes
    from when that helps the developer find more.
14. **Reading values and namespaces.** `entity["col"]` is the value or null; a misspelt or unread attribute
   reads null too, so take column names from the table. `GetAttributeValue<T>` of NULL is `default(T)` (0 for `int`:
   ask for `int?` to tell NULL from 0); it converts numbers when nothing is lost (a Count is always a `long`, Sum and
   Avg are decimal or double by provider: read them as `long` and `decimal`), and reads a declared lookup (an
   `ArxEntityReference`, also in a grouped query) as its id, and a UTC or Local `DateTime` as a `DateTimeOffset` (and
   back, as UTC); a number that doesn't fit is ARX4001 (1.5 as `int`), any other mismatch is ARX4004, an `ArxException`.
   Through a link a lookup column is its plain id, not an `ArxEntityReference`.
   Namespaces: `ArxEntity`, `ArxEntityReference`, `ArxColumnSet`, `ArxSchemaCatalog` and `ArxMatch` are in
   `ARX.SDK.Services`; `ArxQueryExpression`, `ArxConditionOperator`, `ArxJoinOperator`, `ArxAggregateOperator` and
   `ArxOrderType` in `ARX.SDK.Query`; `ArxException` and `ArxErrorCode` in `ARX.SDK`; `ArxPgDbService` and `ArxPgConnection` in `ARX.SDK.PostgreSql.Services`. Write every `using` a file needs.
   Names that differ from the Dynamics XRM SDK: the join operators are `ArxJoinOperator.Inner` and `ArxJoinOperator.Left` (not XRM's `LeftOuter`);
   a link's columns are `link.ColumnSet`, its alias `link.EntityAlias`, its conditions `link.LinkCriteria`; the referenced
   table of an `ArxEntityReference` is `EntityName` and its id `RecordId`. `UpdateAsync` throws ARX2002 RecordNotFound
   when no record matches (`DeleteAsync` returns false or 0 instead). A page's `TotalRecordCount` is an `int`; an aggregate
   Count is a `long`.
15. **Ids and linked columns are plain values.** `entity.RecordId` is an `ArxRecordId`: read it with
    `AsInt64()`, `AsGuid()` or `AsString()`, pass it where an id goes (`RetrieveAsync("account", id)`,
    `new ArxEntityReference("account", entity.RecordId!)`), or pass the plain value instead. `ArxRecordId` is a class, not
    a nullable struct: `RecordId` is null when no id is known, and `.Value` is the id as an `object` (pass the
    `ArxRecordId` itself, or `AsInt64()`, where a typed id goes, never `.Value`). A linked table's column reads back as `row["alias.column"]`, the plain value (no `AliasedValue`); without an alias the prefix is the table's name (`row["account.name"]`). Table names
    are matched exactly (`"Account"` isn't `account`: ARX1016); column names ignoring case.

Before finishing: `dotnet build`, run the tests, and check every ARX call against `arx-postgresql-types.md`. When the
ARX.SDK package version changes, replace the knowledge files with the new version's and update this section.

---
applyTo: "**/*.cs"
---

# ARX.SDK data access

This project uses ARX.SDK 1.0.0-rc.1 with PostgreSQL (package `ARX.SDK.PostgreSql`, service `ArxPgDbService`). Its knowledge
files are in `docs/arx-sdk/references/postgresql/`; the files named below are there.

You help a developer write C# code that uses ARX.SDK with PostgreSQL (package `ARX.SDK.PostgreSql`). Follow these
rules.

1. **Use ARX's types for database work.** Create, update, delete and read rows, call procedures and functions, and run
   transactions through `ArxPgDbService`, `ArxPgConnection` and `ArxTransaction`. Don't write Npgsql code
   (`NpgsqlConnection`, `NpgsqlCommand`) or SQL text for work ARX does.
2. **Don't invent API.** Use only the types, methods, properties and parameters listed in `arx-postgresql-types.md`. If
   something isn't there, say ARX doesn't offer it rather than guessing a name.
3. **A row is an `ArxEntity`.** `var account = new ArxEntity("account");` then values by column name:
   `account["name"] = "Northwind Traders";`. Table and column names are the database's, as strings.
4. **Declare every table's id column once, at startup,** in an `ArxSchemaCatalog`, and give it to the service:
   `ArxSchemaCatalog.Create().Table("account", ArxIdColumn.Generated<long>("id")).Build()`, then
   `new ArxPgDbService(connectionString, schema)`. Use `ArxIdColumn.Supplied<string>("code")` for an id the application
   provides and `ArxIdColumn.NoIdColumn` for a table without one; add business keys with
   `.Key("account", "account_number")`. ARX never guesses an id: an undeclared table is ARX1016. ARX never creates or changes tables: the application's scripts or migrations do, so when the user has no table yet, give its CREATE TABLE too ("Your first table" in the Using your own tables guide has one per database). A service created
   without a catalog (`new ArxPgDbService(connectionString)`) reads each table's primary key and column types from the
   database before every call instead: much slower, only for simple CRUD in small applications (set
   `RememberResolvedTables = true` to read each table once); a table without a usable primary key is then ARX1019. Reads through such a service don't know the id: rows read back have `RecordId` null and lookups come back as their plain ids, so read the id column itself (`row["book_id"]`) or give the service a catalog.
5. **Every call is asynchronous** (`CreateAsync`, `CreateMultipleAsync`, `UpdateAsync`, `UpdateMultipleAsync`,
   `DeleteAsync`, `DeleteMultipleAsync`, `RetrieveAsync`, `RetrieveMultipleAsync`, `ExecuteAsync`); await it, and pass
   the caller's `CancellationToken` where the method takes one.
6. **Create returns the id.** `ArxRecordId id = await service.CreateAsync(entity);` (also set on `entity.RecordId`);
   `CreateMultipleAsync` returns one id per entity, in list order. Point a lookup column at another record with
   `new ArxEntityReference("account", id)`.
7. **Update and Delete find rows by the id, a declared key, or columns you name:**
   `new ArxUpdateOptions { Match = ArxMatch.Key("account_number") }`, `ArxMatch.Columns(...)`. An update changes only
   the attributes that are set; setting one to `null` clears that column.
   **To change or delete every row a condition matches** (from 0.1.0-preview.5): an entity with only the values to set
   and an `ArxFilterExpression`, `int changed = await service.UpdateMultipleAsync(values, filter);`, or
   `await service.DeleteMultipleAsync("account", filter)`; one statement (binary `COPY` for a create of 5,000 rows or more of one shape), all or nothing, returning the count. The
   entity carries no id (ARX1001 with a filter); an empty filter is ARX1001 unless
   `new ArxFilterWriteOptions { AllRows = true }`. For a large insert whose ids aren't needed:
   `CreateMultipleAsync(entities, new ArxCreateMultipleOptions { ReturnIds = false })` (every id `ArxRecordId.None`).
8. **Reads.** `RetrieveAsync` returns `null` when nothing matches. `RetrieveMultipleAsync` takes an
   `ArxQueryExpression` (criteria, columns, order, paging, links to other tables) and returns the rows in `.Entities`.
   **Query cheat sheet** (the exact names; there are no others, such as `AddGroupBy` or `MoreRecords`):
   `var query = new ArxQueryExpression("book");` · columns: `query.ColumnSet = new ArxColumnSet("title", "year");`
   (empty: every column) · conditions: `query.Criteria.AddCondition("year", ArxConditionOperator.Between, 2000, 2010);`
   (Equal, NotEqual, GreaterThan, GreaterEqual, LessThan, LessEqual, Between, In, NotIn, Like, Contains, BeginsWith,
   EndsWith, Null, NotNull and their Not/DoesNot forms) · an OR group: `var either = query.Criteria.AddFilter(ArxLogicalOperator.Or);`
   then `either.AddCondition(…)` · order: `query.AddOrder("title", ArxOrderType.Ascending);`
   · a join: `var author = query.AddLink("author", "author_id", "id", ArxJoinOperator.Inner); author.EntityAlias = "a";
   author.ColumnSet = new ArxColumnSet("name");`, read as `row["a.name"]` · paging:
   `query.PageInfo = new ArxPagingInfo { Count = 20, PageNumber = 1, ReturnTotalRecordCount = true };`, then
   `result.Entities`, `result.HasNextPage`, `result.TotalRecordCount` · grouped counts:
   `query.AggregateInfo = new ArxAggregateInfo(); query.AggregateInfo.AddAggregateColumn("books", "id", ArxAggregateOperator.Count);
   query.AggregateInfo.AddGroupByColumn("author_id");` (Count reads back as a `long`). A foreign key column reads back as
   an `ArxEntityReference` (with the referenced row's name) only when the catalog declares it:
   `.Lookup("book", "author_id", "author")` and `.DisplayName("author", "name")`; otherwise it is the plain id.
9. **Values are always parameters:** pass them as .NET values and never build SQL with them. A table or column name
   that carries SQL is refused with ARX1017, but a valid name is used as given: a name typed by a user can read any
   table or column the database user can (`pg_catalog.pg_roles`, `information_schema.columns`). Never pass a name from a user unchecked: map it to one the
   application allows (an allow list), or preload the schema and set `Strict = true`.
10. **Dates:** `DateTimeOffset` or a UTC `DateTime` for a moment (`timestamptz`), a `DateTime` with Kind `Unspecified`
    for a wall-clock time (`timestamp`), `DateOnly`, `TimeOnly`, `TimeSpan` (`interval`). Never `default(DateTime)`
    (ARX1013: use `null`) and never a date as a string (ARX4004).
11. **Errors** are `ArxException`s with a stable `Code`: catch by code
    (`catch (ArxException error) when (error.Code == ArxErrorCode.UniqueViolation)`: catch the base class, since the class tells where an error was found and the code what happened) and retry only when
    `error.IsTransient` is true. `arx-postgresql-error-codes.md` lists every code.
12. **Transactions:** `await using var connection = new ArxPgConnection(connectionString);`,
    `await using var transaction = await connection.BeginTransactionAsync();`, pass `transaction` to each call, then
    `await transaction.CommitAsync();`. Disposing without committing rolls back. Code written against `IArxDataService` opens one without the provider type: `await using var transaction = await service.BeginTransactionAsync();` (from 0.1.0-preview.5; the transaction owns its connection). For many calls as one unit,
    `await service.RunBatchAsync(async batch => { … });` commits when the body returns.
13. **Base answers on the samples** in the operation files: they are verified code. Say which sample a pattern comes
    from when that helps the developer find more.
14. **Reading values and namespaces.** `entity["col"]` is the value or null; a misspelt or unread attribute
   reads null too, so take column names from the table. `GetAttributeValue<T>` of NULL is `default(T)` (0 for `int`:
   ask for `int?` to tell NULL from 0); it converts numbers when nothing is lost (a Count is always a `long`, Sum and
   Avg are decimal or double by provider: read them as `long` and `decimal`), and reads a declared lookup (an
   `ArxEntityReference`, also in a grouped query) as its id, and a UTC or Local `DateTime` as a `DateTimeOffset` (and
   back, as UTC); a number that doesn't fit is ARX4001 (1.5 as `int`), any other mismatch is ARX4004, an `ArxException`.
   Through a link a lookup column is its plain id, not an `ArxEntityReference`.
   Namespaces: `ArxEntity`, `ArxEntityReference`, `ArxColumnSet`, `ArxSchemaCatalog` and `ArxMatch` are in
   `ARX.SDK.Services`; `ArxQueryExpression`, `ArxConditionOperator`, `ArxJoinOperator`, `ArxAggregateOperator` and
   `ArxOrderType` in `ARX.SDK.Query`; `ArxException` and `ArxErrorCode` in `ARX.SDK`; `ArxPgDbService` and `ArxPgConnection` in `ARX.SDK.PostgreSql.Services`. Write every `using` a file needs.
   Names that differ from the Dynamics XRM SDK: the join operators are `ArxJoinOperator.Inner` and `ArxJoinOperator.Left` (not XRM's `LeftOuter`);
   a link's columns are `link.ColumnSet`, its alias `link.EntityAlias`, its conditions `link.LinkCriteria`; the referenced
   table of an `ArxEntityReference` is `EntityName` and its id `RecordId`. `UpdateAsync` throws ARX2002 RecordNotFound
   when no record matches (`DeleteAsync` returns false or 0 instead). A page's `TotalRecordCount` is an `int`; an aggregate
   Count is a `long`.
15. **Ids and linked columns are plain values.** `entity.RecordId` is an `ArxRecordId`: read it with
    `AsInt64()`, `AsGuid()` or `AsString()`, pass it where an id goes (`RetrieveAsync("account", id)`,
    `new ArxEntityReference("account", entity.RecordId!)`), or pass the plain value instead. `ArxRecordId` is a class, not
    a nullable struct: `RecordId` is null when no id is known, and `.Value` is the id as an `object` (pass the
    `ArxRecordId` itself, or `AsInt64()`, where a typed id goes, never `.Value`). A linked table's column reads back as `row["alias.column"]`, the plain value (no `AliasedValue`); without an alias the prefix is the table's name (`row["account.name"]`). Table names
    are matched exactly (`"Account"` isn't `account`: ARX1016); column names ignoring case.

Check every ARX call against `arx-postgresql-types.md`, and build before finishing.

---
description: Writing or changing data access code that uses ARX.SDK (ARX.SDK.PostgreSql)
globs: **/*.cs
alwaysApply: false
---

# ARX.SDK data access

This project uses ARX.SDK 1.0.0-rc.1 with PostgreSQL (package `ARX.SDK.PostgreSql`, service `ArxPgDbService`). Its knowledge
files are in `docs/arx-sdk/references/postgresql/`; the files named below are there. Read `arx-postgresql-guide.md` and
`arx-postgresql-types.md` before writing data access code.

You help a developer write C# code that uses ARX.SDK with PostgreSQL (package `ARX.SDK.PostgreSql`). Follow these
rules.

1. **Use ARX's types for database work.** Create, update, delete and read rows, call procedures and functions, and run
   transactions through `ArxPgDbService`, `ArxPgConnection` and `ArxTransaction`. Don't write Npgsql code
   (`NpgsqlConnection`, `NpgsqlCommand`) or SQL text for work ARX does.
2. **Don't invent API.** Use only the types, methods, properties and parameters listed in `arx-postgresql-types.md`. If
   something isn't there, say ARX doesn't offer it rather than guessing a name.
3. **A row is an `ArxEntity`.** `var account = new ArxEntity("account");` then values by column name:
   `account["name"] = "Northwind Traders";`. Table and column names are the database's, as strings.
4. **Declare every table's id column once, at startup,** in an `ArxSchemaCatalog`, and give it to the service:
   `ArxSchemaCatalog.Create().Table("account", ArxIdColumn.Generated<long>("id")).Build()`, then
   `new ArxPgDbService(connectionString, schema)`. Use `ArxIdColumn.Supplied<string>("code")` for an id the application
   provides and `ArxIdColumn.NoIdColumn` for a table without one; add business keys with
   `.Key("account", "account_number")`. ARX never guesses an id: an undeclared table is ARX1016. ARX never creates or changes tables: the application's scripts or migrations do, so when the user has no table yet, give its CREATE TABLE too ("Your first table" in the Using your own tables guide has one per database). A service created
   without a catalog (`new ArxPgDbService(connectionString)`) reads each table's primary key and column types from the
   database before every call instead: much slower, only for simple CRUD in small applications (set
   `RememberResolvedTables = true` to read each table once); a table without a usable primary key is then ARX1019. Reads through such a service don't know the id: rows read back have `RecordId` null and lookups come back as their plain ids, so read the id column itself (`row["book_id"]`) or give the service a catalog.
5. **Every call is asynchronous** (`CreateAsync`, `CreateMultipleAsync`, `UpdateAsync`, `UpdateMultipleAsync`,
   `DeleteAsync`, `DeleteMultipleAsync`, `RetrieveAsync`, `RetrieveMultipleAsync`, `ExecuteAsync`); await it, and pass
   the caller's `CancellationToken` where the method takes one.
6. **Create returns the id.** `ArxRecordId id = await service.CreateAsync(entity);` (also set on `entity.RecordId`);
   `CreateMultipleAsync` returns one id per entity, in list order. Point a lookup column at another record with
   `new ArxEntityReference("account", id)`.
7. **Update and Delete find rows by the id, a declared key, or columns you name:**
   `new ArxUpdateOptions { Match = ArxMatch.Key("account_number") }`, `ArxMatch.Columns(...)`. An update changes only
   the attributes that are set; setting one to `null` clears that column.
   **To change or delete every row a condition matches** (from 0.1.0-preview.5): an entity with only the values to set
   and an `ArxFilterExpression`, `int changed = await service.UpdateMultipleAsync(values, filter);`, or
   `await service.DeleteMultipleAsync("account", filter)`; one statement (binary `COPY` for a create of 5,000 rows or more of one shape), all or nothing, returning the count. The
   entity carries no id (ARX1001 with a filter); an empty filter is ARX1001 unless
   `new ArxFilterWriteOptions { AllRows = true }`. For a large insert whose ids aren't needed:
   `CreateMultipleAsync(entities, new ArxCreateMultipleOptions { ReturnIds = false })` (every id `ArxRecordId.None`).
8. **Reads.** `RetrieveAsync` returns `null` when nothing matches. `RetrieveMultipleAsync` takes an
   `ArxQueryExpression` (criteria, columns, order, paging, links to other tables) and returns the rows in `.Entities`.
   **Query cheat sheet** (the exact names; there are no others, such as `AddGroupBy` or `MoreRecords`):
   `var query = new ArxQueryExpression("book");` · columns: `query.ColumnSet = new ArxColumnSet("title", "year");`
   (empty: every column) · conditions: `query.Criteria.AddCondition("year", ArxConditionOperator.Between, 2000, 2010);`
   (Equal, NotEqual, GreaterThan, GreaterEqual, LessThan, LessEqual, Between, In, NotIn, Like, Contains, BeginsWith,
   EndsWith, Null, NotNull and their Not/DoesNot forms) · an OR group: `var either = query.Criteria.AddFilter(ArxLogicalOperator.Or);`
   then `either.AddCondition(…)` · order: `query.AddOrder("title", ArxOrderType.Ascending);`
   · a join: `var author = query.AddLink("author", "author_id", "id", ArxJoinOperator.Inner); author.EntityAlias = "a";
   author.ColumnSet = new ArxColumnSet("name");`, read as `row["a.name"]` · paging:
   `query.PageInfo = new ArxPagingInfo { Count = 20, PageNumber = 1, ReturnTotalRecordCount = true };`, then
   `result.Entities`, `result.HasNextPage`, `result.TotalRecordCount` · grouped counts:
   `query.AggregateInfo = new ArxAggregateInfo(); query.AggregateInfo.AddAggregateColumn("books", "id", ArxAggregateOperator.Count);
   query.AggregateInfo.AddGroupByColumn("author_id");` (Count reads back as a `long`). A foreign key column reads back as
   an `ArxEntityReference` (with the referenced row's name) only when the catalog declares it:
   `.Lookup("book", "author_id", "author")` and `.DisplayName("author", "name")`; otherwise it is the plain id.
9. **Values are always parameters:** pass them as .NET values and never build SQL with them. A table or column name
   that carries SQL is refused with ARX1017, but a valid name is used as given: a name typed by a user can read any
   table or column the database user can (`pg_catalog.pg_roles`, `information_schema.columns`). Never pass a name from a user unchecked: map it to one the
   application allows (an allow list), or preload the schema and set `Strict = true`.
10. **Dates:** `DateTimeOffset` or a UTC `DateTime` for a moment (`timestamptz`), a `DateTime` with Kind `Unspecified`
    for a wall-clock time (`timestamp`), `DateOnly`, `TimeOnly`, `TimeSpan` (`interval`). Never `default(DateTime)`
    (ARX1013: use `null`) and never a date as a string (ARX4004).
11. **Errors** are `ArxException`s with a stable `Code`: catch by code
    (`catch (ArxException error) when (error.Code == ArxErrorCode.UniqueViolation)`: catch the base class, since the class tells where an error was found and the code what happened) and retry only when
    `error.IsTransient` is true. `arx-postgresql-error-codes.md` lists every code.
12. **Transactions:** `await using var connection = new ArxPgConnection(connectionString);`,
    `await using var transaction = await connection.BeginTransactionAsync();`, pass `transaction` to each call, then
    `await transaction.CommitAsync();`. Disposing without committing rolls back. Code written against `IArxDataService` opens one without the provider type: `await using var transaction = await service.BeginTransactionAsync();` (from 0.1.0-preview.5; the transaction owns its connection). For many calls as one unit,
    `await service.RunBatchAsync(async batch => { … });` commits when the body returns.
13. **Base answers on the samples** in the operation files: they are verified code. Say which sample a pattern comes
    from when that helps the developer find more.
14. **Reading values and namespaces.** `entity["col"]` is the value or null; a misspelt or unread attribute
   reads null too, so take column names from the table. `GetAttributeValue<T>` of NULL is `default(T)` (0 for `int`:
   ask for `int?` to tell NULL from 0); it converts numbers when nothing is lost (a Count is always a `long`, Sum and
   Avg are decimal or double by provider: read them as `long` and `decimal`), and reads a declared lookup (an
   `ArxEntityReference`, also in a grouped query) as its id, and a UTC or Local `DateTime` as a `DateTimeOffset` (and
   back, as UTC); a number that doesn't fit is ARX4001 (1.5 as `int`), any other mismatch is ARX4004, an `ArxException`.
   Through a link a lookup column is its plain id, not an `ArxEntityReference`.
   Namespaces: `ArxEntity`, `ArxEntityReference`, `ArxColumnSet`, `ArxSchemaCatalog` and `ArxMatch` are in
   `ARX.SDK.Services`; `ArxQueryExpression`, `ArxConditionOperator`, `ArxJoinOperator`, `ArxAggregateOperator` and
   `ArxOrderType` in `ARX.SDK.Query`; `ArxException` and `ArxErrorCode` in `ARX.SDK`; `ArxPgDbService` and `ArxPgConnection` in `ARX.SDK.PostgreSql.Services`. Write every `using` a file needs.
   Names that differ from the Dynamics XRM SDK: the join operators are `ArxJoinOperator.Inner` and `ArxJoinOperator.Left` (not XRM's `LeftOuter`);
   a link's columns are `link.ColumnSet`, its alias `link.EntityAlias`, its conditions `link.LinkCriteria`; the referenced
   table of an `ArxEntityReference` is `EntityName` and its id `RecordId`. `UpdateAsync` throws ARX2002 RecordNotFound
   when no record matches (`DeleteAsync` returns false or 0 instead). A page's `TotalRecordCount` is an `int`; an aggregate
   Count is a `long`.
15. **Ids and linked columns are plain values.** `entity.RecordId` is an `ArxRecordId`: read it with
    `AsInt64()`, `AsGuid()` or `AsString()`, pass it where an id goes (`RetrieveAsync("account", id)`,
    `new ArxEntityReference("account", entity.RecordId!)`), or pass the plain value instead. `ArxRecordId` is a class, not
    a nullable struct: `RecordId` is null when no id is known, and `.Value` is the id as an `object` (pass the
    `ArxRecordId` itself, or `AsInt64()`, where a typed id goes, never `.Value`). A linked table's column reads back as `row["alias.column"]`, the plain value (no `AliasedValue`); without an alias the prefix is the table's name (`row["account.name"]`). Table names
    are matched exactly (`"Account"` isn't `account`: ARX1016); column names ignoring case.

Check every ARX call against `arx-postgresql-types.md`, and build before finishing.

## Data access: ARX.SDK

This project uses ARX.SDK 1.0.0-rc.1 with PostgreSQL (package `ARX.SDK.PostgreSql`, service `ArxPgDbService`). Its knowledge
files, generated from the library and its verified samples, are in `docs/arx-sdk/references/postgresql/`; the files named
below are there. Read `arx-postgresql-guide.md` and `arx-postgresql-types.md` before writing data access code,
and the operation's file (`arx-postgresql-create.md`, `-create-multiple.md`, `-update.md`, `-update-multiple.md`,
`-delete.md`, `-delete-multiple.md`, `-retrieve.md`, `-retrieve-multiple.md`, `-execute.md`) for its samples.

You help a developer write C# code that uses ARX.SDK with PostgreSQL (package `ARX.SDK.PostgreSql`). Follow these
rules.

1. **Use ARX's types for database work.** Create, update, delete and read rows, call procedures and functions, and run
   transactions through `ArxPgDbService`, `ArxPgConnection` and `ArxTransaction`. Don't write Npgsql code
   (`NpgsqlConnection`, `NpgsqlCommand`) or SQL text for work ARX does.
2. **Don't invent API.** Use only the types, methods, properties and parameters listed in `arx-postgresql-types.md`. If
   something isn't there, say ARX doesn't offer it rather than guessing a name.
3. **A row is an `ArxEntity`.** `var account = new ArxEntity("account");` then values by column name:
   `account["name"] = "Northwind Traders";`. Table and column names are the database's, as strings.
4. **Declare every table's id column once, at startup,** in an `ArxSchemaCatalog`, and give it to the service:
   `ArxSchemaCatalog.Create().Table("account", ArxIdColumn.Generated<long>("id")).Build()`, then
   `new ArxPgDbService(connectionString, schema)`. Use `ArxIdColumn.Supplied<string>("code")` for an id the application
   provides and `ArxIdColumn.NoIdColumn` for a table without one; add business keys with
   `.Key("account", "account_number")`. ARX never guesses an id: an undeclared table is ARX1016. ARX never creates or changes tables: the application's scripts or migrations do, so when the user has no table yet, give its CREATE TABLE too ("Your first table" in the Using your own tables guide has one per database). A service created
   without a catalog (`new ArxPgDbService(connectionString)`) reads each table's primary key and column types from the
   database before every call instead: much slower, only for simple CRUD in small applications (set
   `RememberResolvedTables = true` to read each table once); a table without a usable primary key is then ARX1019. Reads through such a service don't know the id: rows read back have `RecordId` null and lookups come back as their plain ids, so read the id column itself (`row["book_id"]`) or give the service a catalog.
5. **Every call is asynchronous** (`CreateAsync`, `CreateMultipleAsync`, `UpdateAsync`, `UpdateMultipleAsync`,
   `DeleteAsync`, `DeleteMultipleAsync`, `RetrieveAsync`, `RetrieveMultipleAsync`, `ExecuteAsync`); await it, and pass
   the caller's `CancellationToken` where the method takes one.
6. **Create returns the id.** `ArxRecordId id = await service.CreateAsync(entity);` (also set on `entity.RecordId`);
   `CreateMultipleAsync` returns one id per entity, in list order. Point a lookup column at another record with
   `new ArxEntityReference("account", id)`.
7. **Update and Delete find rows by the id, a declared key, or columns you name:**
   `new ArxUpdateOptions { Match = ArxMatch.Key("account_number") }`, `ArxMatch.Columns(...)`. An update changes only
   the attributes that are set; setting one to `null` clears that column.
   **To change or delete every row a condition matches** (from 0.1.0-preview.5): an entity with only the values to set
   and an `ArxFilterExpression`, `int changed = await service.UpdateMultipleAsync(values, filter);`, or
   `await service.DeleteMultipleAsync("account", filter)`; one statement (binary `COPY` for a create of 5,000 rows or more of one shape), all or nothing, returning the count. The
   entity carries no id (ARX1001 with a filter); an empty filter is ARX1001 unless
   `new ArxFilterWriteOptions { AllRows = true }`. For a large insert whose ids aren't needed:
   `CreateMultipleAsync(entities, new ArxCreateMultipleOptions { ReturnIds = false })` (every id `ArxRecordId.None`).
8. **Reads.** `RetrieveAsync` returns `null` when nothing matches. `RetrieveMultipleAsync` takes an
   `ArxQueryExpression` (criteria, columns, order, paging, links to other tables) and returns the rows in `.Entities`.
   **Query cheat sheet** (the exact names; there are no others, such as `AddGroupBy` or `MoreRecords`):
   `var query = new ArxQueryExpression("book");` · columns: `query.ColumnSet = new ArxColumnSet("title", "year");`
   (empty: every column) · conditions: `query.Criteria.AddCondition("year", ArxConditionOperator.Between, 2000, 2010);`
   (Equal, NotEqual, GreaterThan, GreaterEqual, LessThan, LessEqual, Between, In, NotIn, Like, Contains, BeginsWith,
   EndsWith, Null, NotNull and their Not/DoesNot forms) · an OR group: `var either = query.Criteria.AddFilter(ArxLogicalOperator.Or);`
   then `either.AddCondition(…)` · order: `query.AddOrder("title", ArxOrderType.Ascending);`
   · a join: `var author = query.AddLink("author", "author_id", "id", ArxJoinOperator.Inner); author.EntityAlias = "a";
   author.ColumnSet = new ArxColumnSet("name");`, read as `row["a.name"]` · paging:
   `query.PageInfo = new ArxPagingInfo { Count = 20, PageNumber = 1, ReturnTotalRecordCount = true };`, then
   `result.Entities`, `result.HasNextPage`, `result.TotalRecordCount` · grouped counts:
   `query.AggregateInfo = new ArxAggregateInfo(); query.AggregateInfo.AddAggregateColumn("books", "id", ArxAggregateOperator.Count);
   query.AggregateInfo.AddGroupByColumn("author_id");` (Count reads back as a `long`). A foreign key column reads back as
   an `ArxEntityReference` (with the referenced row's name) only when the catalog declares it:
   `.Lookup("book", "author_id", "author")` and `.DisplayName("author", "name")`; otherwise it is the plain id.
9. **Values are always parameters:** pass them as .NET values and never build SQL with them. A table or column name
   that carries SQL is refused with ARX1017, but a valid name is used as given: a name typed by a user can read any
   table or column the database user can (`pg_catalog.pg_roles`, `information_schema.columns`). Never pass a name from a user unchecked: map it to one the
   application allows (an allow list), or preload the schema and set `Strict = true`.
10. **Dates:** `DateTimeOffset` or a UTC `DateTime` for a moment (`timestamptz`), a `DateTime` with Kind `Unspecified`
    for a wall-clock time (`timestamp`), `DateOnly`, `TimeOnly`, `TimeSpan` (`interval`). Never `default(DateTime)`
    (ARX1013: use `null`) and never a date as a string (ARX4004).
11. **Errors** are `ArxException`s with a stable `Code`: catch by code
    (`catch (ArxException error) when (error.Code == ArxErrorCode.UniqueViolation)`: catch the base class, since the class tells where an error was found and the code what happened) and retry only when
    `error.IsTransient` is true. `arx-postgresql-error-codes.md` lists every code.
12. **Transactions:** `await using var connection = new ArxPgConnection(connectionString);`,
    `await using var transaction = await connection.BeginTransactionAsync();`, pass `transaction` to each call, then
    `await transaction.CommitAsync();`. Disposing without committing rolls back. Code written against `IArxDataService` opens one without the provider type: `await using var transaction = await service.BeginTransactionAsync();` (from 0.1.0-preview.5; the transaction owns its connection). For many calls as one unit,
    `await service.RunBatchAsync(async batch => { … });` commits when the body returns.
13. **Base answers on the samples** in the operation files: they are verified code. Say which sample a pattern comes
    from when that helps the developer find more.
14. **Reading values and namespaces.** `entity["col"]` is the value or null; a misspelt or unread attribute
   reads null too, so take column names from the table. `GetAttributeValue<T>` of NULL is `default(T)` (0 for `int`:
   ask for `int?` to tell NULL from 0); it converts numbers when nothing is lost (a Count is always a `long`, Sum and
   Avg are decimal or double by provider: read them as `long` and `decimal`), and reads a declared lookup (an
   `ArxEntityReference`, also in a grouped query) as its id, and a UTC or Local `DateTime` as a `DateTimeOffset` (and
   back, as UTC); a number that doesn't fit is ARX4001 (1.5 as `int`), any other mismatch is ARX4004, an `ArxException`.
   Through a link a lookup column is its plain id, not an `ArxEntityReference`.
   Namespaces: `ArxEntity`, `ArxEntityReference`, `ArxColumnSet`, `ArxSchemaCatalog` and `ArxMatch` are in
   `ARX.SDK.Services`; `ArxQueryExpression`, `ArxConditionOperator`, `ArxJoinOperator`, `ArxAggregateOperator` and
   `ArxOrderType` in `ARX.SDK.Query`; `ArxException` and `ArxErrorCode` in `ARX.SDK`; `ArxPgDbService` and `ArxPgConnection` in `ARX.SDK.PostgreSql.Services`. Write every `using` a file needs.
   Names that differ from the Dynamics XRM SDK: the join operators are `ArxJoinOperator.Inner` and `ArxJoinOperator.Left` (not XRM's `LeftOuter`);
   a link's columns are `link.ColumnSet`, its alias `link.EntityAlias`, its conditions `link.LinkCriteria`; the referenced
   table of an `ArxEntityReference` is `EntityName` and its id `RecordId`. `UpdateAsync` throws ARX2002 RecordNotFound
   when no record matches (`DeleteAsync` returns false or 0 instead). A page's `TotalRecordCount` is an `int`; an aggregate
   Count is a `long`.
15. **Ids and linked columns are plain values.** `entity.RecordId` is an `ArxRecordId`: read it with
    `AsInt64()`, `AsGuid()` or `AsString()`, pass it where an id goes (`RetrieveAsync("account", id)`,
    `new ArxEntityReference("account", entity.RecordId!)`), or pass the plain value instead. `ArxRecordId` is a class, not
    a nullable struct: `RecordId` is null when no id is known, and `.Value` is the id as an `object` (pass the
    `ArxRecordId` itself, or `AsInt64()`, where a typed id goes, never `.Value`). A linked table's column reads back as `row["alias.column"]`, the plain value (no `AliasedValue`); without an alias the prefix is the table's name (`row["account.name"]`). Table names
    are matched exactly (`"Account"` isn't `account`: ARX1016); column names ignoring case.

Before finishing: `dotnet build`, run the tests, and check every ARX call against `arx-postgresql-types.md`. When the
ARX.SDK package version changes, replace the knowledge files with the new version's and update this section.

You help a developer write C# code that uses ARX.SDK with PostgreSQL (package `ARX.SDK.PostgreSql`). Follow these
rules.

1. **Use ARX's types for database work.** Create, update, delete and read rows, call procedures and functions, and run
   transactions through `ArxPgDbService`, `ArxPgConnection` and `ArxTransaction`. Don't write Npgsql code
   (`NpgsqlConnection`, `NpgsqlCommand`) or SQL text for work ARX does.
2. **Don't invent API.** Use only the types, methods, properties and parameters listed in `arx-postgresql-types.md`. If
   something isn't there, say ARX doesn't offer it rather than guessing a name.
3. **A row is an `ArxEntity`.** `var account = new ArxEntity("account");` then values by column name:
   `account["name"] = "Northwind Traders";`. Table and column names are the database's, as strings.
4. **Declare every table's id column once, at startup,** in an `ArxSchemaCatalog`, and give it to the service:
   `ArxSchemaCatalog.Create().Table("account", ArxIdColumn.Generated<long>("id")).Build()`, then
   `new ArxPgDbService(connectionString, schema)`. Use `ArxIdColumn.Supplied<string>("code")` for an id the application
   provides and `ArxIdColumn.NoIdColumn` for a table without one; add business keys with
   `.Key("account", "account_number")`. ARX never guesses an id: an undeclared table is ARX1016. ARX never creates or changes tables: the application's scripts or migrations do, so when the user has no table yet, give its CREATE TABLE too ("Your first table" in the Using your own tables guide has one per database). A service created
   without a catalog (`new ArxPgDbService(connectionString)`) reads each table's primary key and column types from the
   database before every call instead: much slower, only for simple CRUD in small applications (set
   `RememberResolvedTables = true` to read each table once); a table without a usable primary key is then ARX1019. Reads through such a service don't know the id: rows read back have `RecordId` null and lookups come back as their plain ids, so read the id column itself (`row["book_id"]`) or give the service a catalog.
5. **Every call is asynchronous** (`CreateAsync`, `CreateMultipleAsync`, `UpdateAsync`, `UpdateMultipleAsync`,
   `DeleteAsync`, `DeleteMultipleAsync`, `RetrieveAsync`, `RetrieveMultipleAsync`, `ExecuteAsync`); await it, and pass
   the caller's `CancellationToken` where the method takes one.
6. **Create returns the id.** `ArxRecordId id = await service.CreateAsync(entity);` (also set on `entity.RecordId`);
   `CreateMultipleAsync` returns one id per entity, in list order. Point a lookup column at another record with
   `new ArxEntityReference("account", id)`.
7. **Update and Delete find rows by the id, a declared key, or columns you name:**
   `new ArxUpdateOptions { Match = ArxMatch.Key("account_number") }`, `ArxMatch.Columns(...)`. An update changes only
   the attributes that are set; setting one to `null` clears that column.
   **To change or delete every row a condition matches** (from 0.1.0-preview.5): an entity with only the values to set
   and an `ArxFilterExpression`, `int changed = await service.UpdateMultipleAsync(values, filter);`, or
   `await service.DeleteMultipleAsync("account", filter)`; one statement (binary `COPY` for a create of 5,000 rows or more of one shape), all or nothing, returning the count. The
   entity carries no id (ARX1001 with a filter); an empty filter is ARX1001 unless
   `new ArxFilterWriteOptions { AllRows = true }`. For a large insert whose ids aren't needed:
   `CreateMultipleAsync(entities, new ArxCreateMultipleOptions { ReturnIds = false })` (every id `ArxRecordId.None`).
8. **Reads.** `RetrieveAsync` returns `null` when nothing matches. `RetrieveMultipleAsync` takes an
   `ArxQueryExpression` (criteria, columns, order, paging, links to other tables) and returns the rows in `.Entities`.
   **Query cheat sheet** (the exact names; there are no others, such as `AddGroupBy` or `MoreRecords`):
   `var query = new ArxQueryExpression("book");` · columns: `query.ColumnSet = new ArxColumnSet("title", "year");`
   (empty: every column) · conditions: `query.Criteria.AddCondition("year", ArxConditionOperator.Between, 2000, 2010);`
   (Equal, NotEqual, GreaterThan, GreaterEqual, LessThan, LessEqual, Between, In, NotIn, Like, Contains, BeginsWith,
   EndsWith, Null, NotNull and their Not/DoesNot forms) · an OR group: `var either = query.Criteria.AddFilter(ArxLogicalOperator.Or);`
   then `either.AddCondition(…)` · order: `query.AddOrder("title", ArxOrderType.Ascending);`
   · a join: `var author = query.AddLink("author", "author_id", "id", ArxJoinOperator.Inner); author.EntityAlias = "a";
   author.ColumnSet = new ArxColumnSet("name");`, read as `row["a.name"]` · paging:
   `query.PageInfo = new ArxPagingInfo { Count = 20, PageNumber = 1, ReturnTotalRecordCount = true };`, then
   `result.Entities`, `result.HasNextPage`, `result.TotalRecordCount` · grouped counts:
   `query.AggregateInfo = new ArxAggregateInfo(); query.AggregateInfo.AddAggregateColumn("books", "id", ArxAggregateOperator.Count);
   query.AggregateInfo.AddGroupByColumn("author_id");` (Count reads back as a `long`). A foreign key column reads back as
   an `ArxEntityReference` (with the referenced row's name) only when the catalog declares it:
   `.Lookup("book", "author_id", "author")` and `.DisplayName("author", "name")`; otherwise it is the plain id.
9. **Values are always parameters:** pass them as .NET values and never build SQL with them. A table or column name
   that carries SQL is refused with ARX1017, but a valid name is used as given: a name typed by a user can read any
   table or column the database user can (`pg_catalog.pg_roles`, `information_schema.columns`). Never pass a name from a user unchecked: map it to one the
   application allows (an allow list), or preload the schema and set `Strict = true`.
10. **Dates:** `DateTimeOffset` or a UTC `DateTime` for a moment (`timestamptz`), a `DateTime` with Kind `Unspecified`
    for a wall-clock time (`timestamp`), `DateOnly`, `TimeOnly`, `TimeSpan` (`interval`). Never `default(DateTime)`
    (ARX1013: use `null`) and never a date as a string (ARX4004).
11. **Errors** are `ArxException`s with a stable `Code`: catch by code
    (`catch (ArxException error) when (error.Code == ArxErrorCode.UniqueViolation)`: catch the base class, since the class tells where an error was found and the code what happened) and retry only when
    `error.IsTransient` is true. `arx-postgresql-error-codes.md` lists every code.
12. **Transactions:** `await using var connection = new ArxPgConnection(connectionString);`,
    `await using var transaction = await connection.BeginTransactionAsync();`, pass `transaction` to each call, then
    `await transaction.CommitAsync();`. Disposing without committing rolls back. Code written against `IArxDataService` opens one without the provider type: `await using var transaction = await service.BeginTransactionAsync();` (from 0.1.0-preview.5; the transaction owns its connection). For many calls as one unit,
    `await service.RunBatchAsync(async batch => { … });` commits when the body returns.
13. **Base answers on the samples** in the operation files: they are verified code. Say which sample a pattern comes
    from when that helps the developer find more.
14. **Reading values and namespaces.** `entity["col"]` is the value or null; a misspelt or unread attribute
   reads null too, so take column names from the table. `GetAttributeValue<T>` of NULL is `default(T)` (0 for `int`:
   ask for `int?` to tell NULL from 0); it converts numbers when nothing is lost (a Count is always a `long`, Sum and
   Avg are decimal or double by provider: read them as `long` and `decimal`), and reads a declared lookup (an
   `ArxEntityReference`, also in a grouped query) as its id, and a UTC or Local `DateTime` as a `DateTimeOffset` (and
   back, as UTC); a number that doesn't fit is ARX4001 (1.5 as `int`), any other mismatch is ARX4004, an `ArxException`.
   Through a link a lookup column is its plain id, not an `ArxEntityReference`.
   Namespaces: `ArxEntity`, `ArxEntityReference`, `ArxColumnSet`, `ArxSchemaCatalog` and `ArxMatch` are in
   `ARX.SDK.Services`; `ArxQueryExpression`, `ArxConditionOperator`, `ArxJoinOperator`, `ArxAggregateOperator` and
   `ArxOrderType` in `ARX.SDK.Query`; `ArxException` and `ArxErrorCode` in `ARX.SDK`; `ArxPgDbService` and `ArxPgConnection` in `ARX.SDK.PostgreSql.Services`. Write every `using` a file needs.
   Names that differ from the Dynamics XRM SDK: the join operators are `ArxJoinOperator.Inner` and `ArxJoinOperator.Left` (not XRM's `LeftOuter`);
   a link's columns are `link.ColumnSet`, its alias `link.EntityAlias`, its conditions `link.LinkCriteria`; the referenced
   table of an `ArxEntityReference` is `EntityName` and its id `RecordId`. `UpdateAsync` throws ARX2002 RecordNotFound
   when no record matches (`DeleteAsync` returns false or 0 instead). A page's `TotalRecordCount` is an `int`; an aggregate
   Count is a `long`.
15. **Ids and linked columns are plain values.** `entity.RecordId` is an `ArxRecordId`: read it with
    `AsInt64()`, `AsGuid()` or `AsString()`, pass it where an id goes (`RetrieveAsync("account", id)`,
    `new ArxEntityReference("account", entity.RecordId!)`), or pass the plain value instead. `ArxRecordId` is a class, not
    a nullable struct: `RecordId` is null when no id is known, and `.Value` is the id as an `object` (pass the
    `ArxRecordId` itself, or `AsInt64()`, where a typed id goes, never `.Value`). A linked table's column reads back as `row["alias.column"]`, the plain value (no `AliasedValue`); without an alias the prefix is the table's name (`row["account.name"]`). Table names
    are matched exactly (`"Account"` isn't `account`: ARX1016); column names ignoring case.