Relational: Populate collections in projection before calling into cl…

…ient code

The shapers on relational now take ResultContext which stores object[] of temporary values. Then populate the collection fully. Then call into client code to generate final result.

Resolves #16318

src/EFCore.Relational/Query/RelationalShapedQueryCompilingExpressionVisitor.AsyncQueryingEnumerable.cs

@@ -19,7 +19,7 @@ private class AsyncQueryingEnumerable<T> : IAsyncEnumerable<T>
  {
  private readonly RelationalQueryContext _relationalQueryContext;
  private readonly SelectExpression _selectExpression;
- private readonly Func<QueryContext, DbDataReader, T, int[], ResultCoordinator, T> _shaper;
+ private readonly Func<QueryContext, DbDataReader, ResultContext, int[], ResultCoordinator, T> _shaper;
  private readonly IQuerySqlGeneratorFactory _querySqlGeneratorFactory;
  private readonly Type _contextType;
  private readonly IDiagnosticsLogger<DbLoggerCategory.Query> _logger;
@@ -32,7 +32,7 @@ public AsyncQueryingEnumerable(
  ISqlExpressionFactory sqlExpressionFactory,
  IParameterNameGeneratorFactory parameterNameGeneratorFactory,
  SelectExpression selectExpression,
- Func<QueryContext, DbDataReader, T, int[], ResultCoordinator, T> shaper,
+ Func<QueryContext, DbDataReader, ResultContext, int[], ResultCoordinator, T> shaper,
  Type contextType,
  IDiagnosticsLogger<DbLoggerCategory.Query> logger)
  {
@@ -56,7 +56,7 @@ private sealed class AsyncEnumerator : IAsyncEnumerator<T>
  private ResultCoordinator _resultCoordinator;
  private readonly RelationalQueryContext _relationalQueryContext;
  private readonly SelectExpression _selectExpression;
- private readonly Func<QueryContext, DbDataReader, T, int[], ResultCoordinator, T> _shaper;
+ private readonly Func<QueryContext, DbDataReader, ResultContext, int[], ResultCoordinator, T> _shaper;
  private readonly IQuerySqlGeneratorFactory _querySqlGeneratorFactory;
  private readonly Type _contextType;
  private readonly IDiagnosticsLogger<DbLoggerCategory.Query> _logger;
@@ -147,15 +147,22 @@ public async ValueTask<bool> MoveNextAsync()
  {
  _resultCoordinator.ResultReady = true;
  _resultCoordinator.HasNext = null;
- Current = _shaper(_relationalQueryContext, _dataReader.DbDataReader, Current, _indexMap, _resultCoordinator);
+ Current = _shaper(_relationalQueryContext, _dataReader.DbDataReader,
+ _resultCoordinator.ResultContext, _indexMap, _resultCoordinator);
  if (_resultCoordinator.ResultReady)
  {
+ // We generated a result so null out previously stored values
+ _resultCoordinator.ResultContext.Values = null;
  break;
  }
 
  if (!await _dataReader.ReadAsync())
  {
  _resultCoordinator.HasNext = false;
+ // Enumeration has ended, materialize last element
+ _resultCoordinator.ResultReady = true;
+ Current = _shaper(_relationalQueryContext, _dataReader.DbDataReader,
+ _resultCoordinator.ResultContext, _indexMap, _resultCoordinator);
 
  break;
  }