Tables
DataTableCollection dtc = DataSet.Tables;
Accesses the DataTableCollection contained by the
DataSet that contains the
DataTable objects belonging to the
DataSet.
The DataTableCollection has two methods that can
add a table to a DataSet. The Add( ) method takes an optional table name argument and is used
to add tables to the DataTableCollection. If this
argument isn’t supplied, the tables are
automatically named Table,
Table1, Table2, and so on. The
following example adds a table to a DataSet:
DataSet ds = new DataSet("MyDataSet");
DataTable dt = new DataTable("MyTable");
// ... code to define the schema for the newly constructed DataTable
ds.Tables.Add(dt);Alternatively, a DataTable can first be
constructed within the DataTablesCollection and
subsequently have its schema defined:
DataSet ds = new DataSet("MyDataSet");
DataTable dt = ds.Tables.Add("MyTable");
// ... code to define the schema for newly constructed DataTableA reference to the table that already exists within the
DataSet can be retrieved. Most commonly, this is
done using the table name or the table ordinal as shown in these
examples:
// using the table name
DataTable dt = ds.Tables("MyTable");
// using the table ordinal
DataTable dt = ds.Tables[0];The Count property returns the number of tables in
the DataSet, as shown here:
Int32 tableCount = ds.Tables.Count;
The Contains( ) method returns whether a specific
DataTable exists within a
DataSet, as shown next:
bool tableExists = ds.Tables.Contains("MyTable");Existing tables within the DataSet can be accessed
by an indexer, which most commonly is passed the table name or the
position of the table within the
DataTableCollection as an argument as shown in
these examples:
// using the table name DataTable dt = ds.Tables["MyTable"]; // access the first table in the collection using the table ordinal DataTable dt = ds.Tables[0];
The IndexOf( ) method allows the index of the
table within the collection to be retrieved using either a reference
to the table object or the table name. The following example
demonstrates both techniques:
// get the index using the name of the table
Int32 tableIndex = ds.Tables.IndexOf("MyTable");
// get the index using a reference to a table
DataTable dt = ds.Tables.Add("MyTable");
// ... build the table and do some work
// get the index of the table based on the table reference
Int32 tableIndex = ds.Tables.IndexOf(dt);The DataTableCollection provides a number of other
useful methods and properties. The AddRange( )
method allows more than one table to be added to the
DataSet at the same time. The method takes an
array of DataTable objects as the argument as the
following examples show:
// create two new tables
DataTable dt1 = new DataTable();
DataTable dt2 = new DataTable();
// use the AddRange method to add them to the DataSet.
ds.Tables.AddRange(new DataTable[] {dt1, dt2});There are also two methods that remove tables from a
DataSet: the Remove( ) and
RemoveAt( ) method. The Remove( ) method takes either the table name or a reference to the
table to be removed as an argument as shown in the following example:
DataTable dt = ds.Tables.Add("MyTable");
// remove by table reference
ds.Tables.Remove(dt);
// remove using the table name
ds.Tables.Remove("MyTable");The RemoveAt( ) method removes the table using the
index of the table in the DataSetCollection of the
DataSet as shown in the following example:
// removes the first table from the tables collection in the DataSet ds.Tables.RemoveAt(0);
If you need to remove all tables from a DataSet,
the Clear( ) method can be used. It takes no
arguments and can be used as shown next:
ds.Tables.Clear();
The commonly used public properties of the
DataTableCollection are listed and described in
Table 22-11.
The commonly used public methods of the
DataTableCollection are listed and described in
Table 22-12.