Delete · DynamoDB in C#

What a delete does

Rule	On DynamoDB
Which item	By its full key: the id (an entity whose key is its id), the id with the key's other attributes, or `ArxMatch.Columns`/`ArxMatch.Key` naming the key's attributes
Other columns	When they give a partition key, of the table or an index: one query finds the items (at most 100), then they are deleted by their keys, all or nothing, each conditioned on still matching; none found is 0 (ARX2002 with RequireSingleRow), several with RequireSingleRow ARX2003
No partition	ARX8001: a write never scans
Nothing found	`DeleteAsync(name, id)` returns false; `DeleteAsync(entity)` returns 0: deleting twice isn't an error
In a transaction	The items are read now (so the count is known), and deleted with the transaction's other writes at the commit
Names	Placeholders only; expression or SQL syntax in a match name is ARX1017, checked before the match itself
Rows by a condition	Delete finds rows by equal values: the id, a declared key, or columns you give values for (`ArxMatch.Columns`). To delete every row that meets a condition (`amount > 100`), call `DeleteMultipleAsync(table, filter)` (the filter must give a partition key; at most 100 items): one call, all or nothing, from 0.1.0-preview.5 (DeleteMultiple, Basics). Before that version: read the rows with `RetrieveMultipleAsync` and pass them to `DeleteMultipleAsync`.

The samples

Basics

The least code that works.

1Delete one recordProgressive

The smallest delete, in two scenarios: by the id Create returned, and an id no item has.

2How a delete finds its itemsProgressive

How a delete finds its items in DynamoDB, in four scenarios: an order by its id and its customer, several orders by their keys, the rest of a customer's orders through a query, and a match no partition answers.

Real cases

What an application does: a small CRM and product catalogue.

1Catch an injection attemptProgressive

A "remove my order" endpoint attacked two ways: a match column named with expression syntax, and a value written to widen the delete to every order; then the honest request.

Advanced cases

Dependency injection, transactions, batch scopes and setting the service up.

1Replace a record in a transactionAdvanced

Replace an order in one ARX transaction: delete the old one, create the new one, commit, in two scenarios: the replacement, and a replacement that fails and leaves the old order in place.

2A security check around deletesAdvanced

A security check around deletes (SecurityGuard), in three scenarios: a normal delete, an attack in the match that is logged, and repeated attacks that block the user.

3Set up the service from DynamoDB's tablesAdvanced

The service set up from DynamoDB's description of the lead table, in two scenarios: preload at startup in the KeysOnly mode, then delete by the preloaded key.