DbDataAdapter.Fill Method (DataTable)
Assembly: System.Data (in System.Data.dll)
The Fill method retrieves rows from the data source using the SELECT statement specified by an associated SelectCommand property. The connection object associated with the SELECT statement must be valid, but it does not need to be open. If the connection is closed before Fill is called, it is opened to retrieve data, then closed. If the connection is open before Fill is called, it remains open.
The Fill operation then adds the rows to destination DataTable objects in the DataSet, creating the DataTable objects if they do not already exist. When creating DataTable objects, the Fill operation normally creates only column name metadata. However, if the MissingSchemaAction property is set to AddWithKey, appropriate primary keys and constraints are also created.
If the DbDataAdapter 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.
The Fill method supports scenarios where the DataSet contains multiple DataTable objects whose names differ only by case. In such situations, Fill 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.Fill(dataset, "aaa"); // Fills "aaa", which already exists in the DataSet. adapter.Fill(dataset, "Aaa"); // Adds a new table called "Aaa".
If Fill 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.Fill(dataset, "AAA"); // Fills table "aaa" because only one similarly named table is in the DataSet.
You can use the Fill method multiple times on the same DataTable. If a primary key exists, incoming rows are merged with matching rows that already exist. If no primary key exists, incoming rows are appended to the DataTable.
If the SelectCommand returns the results of an OUTER JOIN, the DataAdapter does not set a PrimaryKey value for the resulting DataTable. You must explicitly define the primary key to ensure that duplicate rows are resolved correctly. For more information, see Defining Primary Keys.
This overload of the Fill method is protected and is designed for use by a .NET Framework data provider.