Evolve the DbDataReader enumerability story

[roji]

DbDataReader currently implements non-generic IEnumerable only, with no default implement (abstract). Implementations typically return a DbEnumerator (source) instance, which exposes DbDataRecords as the elements.

The problems with the current situation are:

• The lack of a generic IEnumerable implementation
• The lack of async enumeration support
• DbDataRecord lacks an async field access API (GetFieldValue<T>, like on DbDataReader)
  • It should be noted that DbDataRecord itself also lacks async access APIs. This probably makes sense, as it represents a record/row that has been fully loaded into memory, and no actual I/O is meant to take place when its columns are accessed.
  • This also allows older DbDataRecord instances to be retained after new ones have been read via the same DbDataReader.
  • If the user is interested in streaming column access, they can use DbDataReader directly, rather than going through IEnumerable/IAsyncEnumerable.

In an ideal world, we'd make DbDataReader implement IEnumerable<DbDataRecord> and IAsyncEnumerable<DbDataRecord>; the default implementations for these would return an enumerator implementation from System.Data - either a DbEnumerator retro-fitted to work with DbDataReader and its async APIs (DbEnumerator currently works with IDataReader), or a new implementation.

Leaving this issue open for now, to gather more user feedback, as we haven't seen much interest in this (but see previous discussion in #98890).

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Issue Details

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DbDataReader currently implements non-generic IEnumerable only, with no default implement (abstract). Implementations typically return a DbEnumerator (source) instance, which exposes DbDataRecords as the elements.

The problems with the current situation are:

• The lack of a generic IEnumerable implementation
• The lack of async enumeration support
• DbDataRecord lacks an async field access API (GetFieldValue<T>, like on DbDataReader)
  • It should be noted that DbDataRecord itself also lacks async access APIs. This probably makes sense, as it represents a record/row that has been fully loaded into memory, and no actual I/O is meant to take place when its columns are accessed.
  • This also allows older DbDataRecord instances to be retained after new ones have been read via the same DbDataReader.
  • If the user is interested in streaming column access, they can use DbDataReader directly, rather than going through IEnumerable/IAsyncEnumerable.

In an ideal world, we'd make DbDataReader implement IEnumerable<DbDataRecord> and IAsyncEnumerable<DbDataRecord>; the default implementations for these would return an enumerator implementation from System.Data - either a DbEnumerator retro-fitted to work with DbDataReader and its async APIs (DbEnumerator currently works with IDataReader), or a new implementation.

Leaving this issue open for now, to gather more user feedback, as we haven't seen much interest in this (but see previous discussion in #98890).

Author:	roji
Assignees:	-
Labels:	api-suggestion, area-System.Data
Milestone:	-

[nahakyuu]

I am interested in this. When writing some dynamic queries, if the IAsyncEnumerable interface is implemented, it will be convenient to use System.Linq.Async