How To Change DataType of a DataColumn in a DataTa

Question

I have:

DataTable Table = new DataTable;
SqlConnection = new System.Data.SqlClient.SqlConnection("Data Source=" + ServerName + ";Initial Catalog=" + DatabaseName + ";Integrated Security=SSPI; Connect Timeout=120");

SqlDataAdapter adapter = new SqlDataAdapter("Select * from " + TableName, Connection);
adapter.FillSchema(Table, SchemaType.Source);
adapter.Fill(Table);

DataColumn column = DataTable.Columns[0];

What I want to do is:

Assume currently column.DataType.Name is "Double". I want it to become "Int32".

How do I achieve this?

Answer 1

if you want to change only a column.for example from string to int32 you can use expression.

DataColumn col = new DataColumn("col_int" , typeof(int));
table.columns.Add(col)
col.Expression = "table_exist_col_string"; // digit string convert to int  

Answer 2

You cannot change the DataType after the Datatable is filled with data. However, you can clone the Data table, change the column type and load data from previous data table to the cloned table as shown below.

DataTable dtCloned = dt.Clone();
dtCloned.Columns[0].DataType = typeof(Int32);
foreach (DataRow row in dt.Rows) 
{
    dtCloned.ImportRow(row);
}

Answer 3

DataTable DT = ...
// Rename column to OLD:
DT.Columns["ID"].ColumnName = "ID_OLD";
// Add column with new type:
DT.Columns.Add( "ID", typeof(int) );
// copy data from old column to new column with new type:
foreach( DataRow DR in DT.Rows )
{ DR["ID"] = Convert.ToInt32( DR["ID_OLD"] ); }
// remove "OLD" column
DT.Columns.Remove( "ID_OLD" );

Answer 4

Old post, but I thought I'd weigh in, with a DataTable extension that can convert a single column at a time, to a given type:

public static class DataTableExt
{
    public static void ConvertColumnType(this DataTable dt, string columnName, Type newType)
    {
        using (DataColumn dc = new DataColumn(columnName + "_new", newType))
        {
            // Add the new column which has the new type, and move it to the ordinal of the old column
            int ordinal = dt.Columns[columnName].Ordinal;
            dt.Columns.Add(dc);
            dc.SetOrdinal(ordinal);

            // Get and convert the values of the old column, and insert them into the new
            foreach (DataRow dr in dt.Rows)
                dr[dc.ColumnName] = Convert.ChangeType(dr[columnName], newType);

            // Remove the old column
            dt.Columns.Remove(columnName);

            // Give the new column the old column's name
            dc.ColumnName = columnName;
        }
    }
}

It can then be called like this:

MyTable.ConvertColumnType("MyColumnName", typeof(int));

Of course using whatever type you desire, as long as each value in the column can actually be converted to the new type.