Return null from GetSchemaTable when there's no result set. Fixes #877

Author: bgrainger

src/MySqlConnector/MySql.Data.MySqlClient/MySqlDataReader.cs

@@ -293,7 +293,7 @@ public override long GetChars(int ordinal, long dataOffset, char[]? buffer, int
 		public override int VisibleFieldCount => FieldCount;
 
 #if !NETSTANDARD1_3
-		public override DataTable GetSchemaTable() => m_schemaTable ??= BuildSchemaTable();
+		public override DataTable? GetSchemaTable() => m_schemaTable ??= BuildSchemaTable();
 
 		public override void Close() => DisposeAsync(IOBehavior.Synchronous, CancellationToken.None).GetAwaiter().GetResult();
 #endif
@@ -409,14 +409,14 @@ internal static async Task<MySqlDataReader> CreateAsync(CommandListPosition comm
 		}
 
 #if !NETSTANDARD1_3
-		internal DataTable BuildSchemaTable()
+		internal DataTable? BuildSchemaTable()
 		{
-			var schemaTable = new DataTable("SchemaTable") { Locale = CultureInfo.InvariantCulture };
+			var columnDefinitions = m_resultSet?.ColumnDefinitions;
+			if (columnDefinitions is null || m_resultSet!.ContainsCommandParameters)
+				return null;
 
-			var colDefinitions = m_resultSet?.ColumnDefinitions;
-			if (colDefinitions is null || m_resultSet!.ContainsCommandParameters)
-				return schemaTable;
-			schemaTable.MinimumCapacity = colDefinitions.Length;
+			var schemaTable = new DataTable("SchemaTable") { Locale = CultureInfo.InvariantCulture };
+			schemaTable.MinimumCapacity = columnDefinitions.Length;
 
 			var columnName = new DataColumn(SchemaTableColumn.ColumnName, typeof(string));
 			var ordinal = new DataColumn(SchemaTableColumn.ColumnOrdinal, typeof(int));

tests/Conformance.Tests/DataReaderTests.cs

@@ -13,7 +13,7 @@ public DataReaderTests(SelectValueFixture fixture)
 		[Fact(Skip = "Deliberately throws InvalidCastException")]
 		public override void GetTextReader_returns_empty_for_null_String() { }
 
-		[Fact(Skip = "https://github.com/mysql-net/MySqlConnector/issues/744")]
+		[Fact(Skip = "https://github.com/mysql-net/MySqlConnector/issues/877")]
 		public override void GetSchemaTable_throws_after_Delete() { }
 	}
 }

tests/SideBySide/DataTypes.cs

@@ -1192,14 +1192,7 @@ public void GetSchemaTableAfterNextResult()
 			}
 
 			Assert.False(reader.NextResult());
-#if BASELINE
 			Assert.Null(reader.GetSchemaTable());
-#else
-			table = reader.GetSchemaTable();
-			Assert.NotNull(table);
-			Assert.Empty(table.Rows);
-			Assert.Empty(table.Columns);
-#endif
 		}
 #endif
 

tests/SideBySide/StoredProcedureTests.cs

@@ -189,9 +189,7 @@ public async Task GetSchemaTableForNoResultSet(bool ignorePrepare)
 			using var reader = await cmd.ExecuteReaderAsync();
 			Assert.False(await reader.ReadAsync());
 			var table = reader.GetSchemaTable();
-			Assert.NotNull(table);
-			Assert.Empty(table.Rows);
-			Assert.Empty(table.Columns);
+			Assert.Null(table);
 			Assert.False(await reader.NextResultAsync());
 		}
 #endif