[electricessence]

table.Map<T>(): map the rows of a DataTable you already have, for 11.0.0-rc.4 (API shape).

using DataTable table = reader.ToDataTable();
List<Post> posts = table.Map<Post>().ToList();

What

• table.Map<T>() returns MappedTable<T>, a readonly record struct that implements IMappedQuery<T> with the reader view's members (every terminal in sync and async form, Read/ReadAsync, Skip/Take). No SingleResult(), since a table has one result set.
• The same 5 Map<T> overloads as on IDataReader and IDbCommand: the same parameter lists, OverloadResolutionPriority values and guards. A null map maps like Map<T>().
• It is a shortcut for table.CreateDataReader().Map<T>(), which keeps working. The difference is ownership: the view creates and disposes its own reader.

Ownership

• Each terminal reads the table's current rows through a new DataTableReader and disposes it. The table is not changed or cleared, so the view can be read more than once. No connection is involved, and NextResult is never called.
• The asynchronous terminals complete synchronously, because the rows are in memory. A cancelled token gives a cancelled task.

Deprecations now point here

• The messages for To<T>(DataTable, map, clearSourceTable), Transformer<T>.Results(DataTable, bool) and ResultsFromDataTable<T> name table.Map(map).ToList(). So do their rows in whats-new-11 and the ResultsFromDataTable "after" sample.

Docs and tests

• mapping.md gets a short DataTable section with a compiled sample that the samples run checks. whats-new-11 lists the addition.
• MappedTableTests covers:
  • parity with the reader view for every terminal (sync and async);
  • reading the same view twice, with the table unchanged;
  • a Read abandoned part way;
  • null and empty maps;
  • a single-value T;
  • an empty table;
  • Skip/Take;
  • cancellation;
  • a default struct;
  • null arguments.

Checks

• Release and Debug builds: 0 warnings, 0 errors. Tests: 9677 of 9677 pass in both. Samples: 103 of 103 checks pass. Style and analyzers: 0 findings. DocFX: 0 warnings.

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