DbDataAdapter.FillSchema Method (DataSet, SchemaType, IDbCommand, String, CommandBehavior)
[Visual Basic] Overloads Protected Overridable Function FillSchema( _ ByVal dataSet As DataSet, _ ByVal schemaType As SchemaType, _ ByVal command As IDbCommand, _ ByVal srcTable As String, _ ByVal behavior As CommandBehavior _ ) As DataTable() [C#] protected virtual DataTable FillSchema( DataSet dataSet, SchemaType schemaType, IDbCommand command, string srcTable, CommandBehavior behavior ); [C++] protected: virtual DataTable* FillSchema( DataSet* dataSet, SchemaType schemaType, IDbCommand* command, String* srcTable, CommandBehavior behavior ) ; [JScript] protected function FillSchema( dataSet : DataSet, schemaType : SchemaType, command : IDbCommand, srcTable : String, behavior : CommandBehavior ) : DataTable;
- The DataSet to be filled with the schema from the data source.
- One of the SchemaType values.
- The SQL SELECT statement used to retrieve rows from the data source.
- The name of the source table to use for table mapping.
- One of the CommandBehavior values.
An array of DataTable objects that contain schema information returned from the data source.
The FillSchema method retrieves the schema from the data source using the SelectCommand. The connection object associated with the SelectCommand must be valid, but it does not need to be open. If the connection is closed before FillSchema is called, it is opened to retrieve data, then closed. If the connection is open before FillSchema is called, it remains open.
A FillSchema operation adds a DataTable to the destination DataSet. It then adds columns to the DataColumnCollection of the DataTable, and configures the following DataColumn properties if they exist at the data source:
- AutoIncrement. You must set AutoIncrementStep and AutoIncrementSeed separately.
- If one or more primary key columns are returned by the SelectCommand, they are used as the primary key columns for the DataTable.
- If no primary key columns are returned but unique columns are, the unique columns are used as the primary key if, and only if, all the unique columns are nonnullable. If any of the columns are nullable, a UniqueConstraint is added to the ConstraintCollection, but the PrimaryKey property is not set.
- If both primary key columns and unique columns are returned, the primary key columns are used as the primary key columns for the DataTable.
Note that primary keys and unique constraints are added to the ConstraintCollection according to the preceding rules, but other constraint types are not added.
If the IDataAdapter encounters duplicate columns while populating a DataTable, it generates names for the subsequent columns, using the pattern "columnname1", "columnname2", "columnname3", and so on. If the incoming data contains unnamed columns, they are placed in the DataSet according to the pattern "Column1", "Column2", and so on. When multiple result sets are added to the DataSet each result set is placed in a separate table. Additional result sets are named by appending integral values to the specified table name (for example, "Table", "Table1", "Table2", and so on.). Applications should use caution when using column and table names to ensure that conflicts with these naming patterns does not occur.
The FillSchema method supports scenarios where the DataSet contains multiple DataTable objects whose names differ only by case. In such situations, FillSchema performs a case-sensitive comparison to find the corresponding table, and creates a new table if no exact match exists. The following C# code illustrates this behavior.
DataSet dataset = new DataSet(); dataset.Tables.Add("aaa"); dataset.Tables.Add("AAA"); adapter.FillSchema(dataset, "aaa"); // Fills the schema of "aaa", which already exists in the DataSet. adapter.FillSchema(dataset, "Aaa"); // Adds a new table called "Aaa".
If FillSchema is called and the DataSet contains only one DataTable whose name differs only by case, that DataTable is updated. In this scenario, the comparison is case insensitive. The following C# code illustrates this behavior.
DataSet dataset = new DataSet(); dataset.Tables.Add("aaa"); adapter.FillSchema(dataset, "AAA"); // Fills the schema of table "aaa" because only one similarly named table is in the DataSet.
FillSchema does not return any rows. Use the Fill method to add rows to a DataTable.
Note When handling batch SQL statements that return multiple results, the implementation of FillSchema for the .NET Framework Data Provider for OLE DB retrieves schema information for only the first result. To retrieve schema information for multiple results, use Fill with the MissingSchemaAction set to AddWithKey.
When using FillSchema, the .NET Framework Data Provider for SQL Server appends a FOR BROWSE clause to the statement being executed. The user should be aware of potential side effects, such as interference with the use of SET FMTONLY ON statements. See SQL Server Books Online for more information.
Notes to Implementers: This implementation of the FillSchema method is protected and is designed for use by a .NET Framework data provider.
Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework