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The Fill method of the MsDb2DataAdapter fills a dataset only with table columns and rows from a data source; though constraints are commonly set by the data source, the Fill method does not add this schema information to the dataset by default. To populate a dataset with existing primary key constraint information from a data source, you can either call the FillSchema method of the MsDb2DataAdapter, or set the MissingSchemaAction property of the MsDb2DataAdapter to AddWithKey before calling Fill. This ensures that primary key constraints in the dataset reflect those at the data source. Foreign key constraint information is not included and must be created explicitly.
Adding schema information to a DataSet object before filling it with data ensures that primary key constraints are included with the DataTable objects in the DataSet object. As a result, when additional calls to fill the DataSet are made, the primary key column information is used to match new rows from the data source with current rows in each DataTable object, and current data in the tables is overwritten with data from the data source. Without the schema information, the new rows from the data source are appended to the DataSet, resulting in duplicate rows.
Note
If a column in a data source is identified as auto-incrementing, the FillSchema method, or the Fill method with a MissingSchemaAction of AddWithKey, creates a DataColumn with an AutoIncrement property set to true. However, you must set the AutoIncrementStep and AutoIncrementSeed values yourself.
Using the FillSchema method or setting the MissingSchemaAction to AddWithKey requires extra processing at the data source to determine primary key column information. This additional processing can hinder performance. If you know the primary key information at design time, we recommend that you explicitly specify the primary key column or columns in order to achieve optimal performance.
If the MsDb2DataAdapter encounters multiple result sets returned from the SelectCommand property, it creates multiple tables in the dataset. The tables are given a zero-based incremental default name of TableN, starting with Table instead of "Table0". If a table name is passed as an argument to the FillSchema method, the tables are given a zero-based incremental name of TableNameN, starting with TableName instead of "TableName0".