CODEWITHSUNDEEP
c#datatable
sigil
sigil

Reputation: 9546

Set autonumber for DataTable after it already has data

I have the following code to add an autonumber column to a DataTable:

public void AddAutoIncrementColumn(DataTable dt)
{
   DataColumn column = new DataColumn();
   column.DataType = System.Type.GetType("System.Int32");
   column.AutoIncrement = true;
   column.AutoIncrementSeed = 0;
   column.AutoIncrementStep = 1;
   dt.Columns.Add(column);
}

However, this value will be blank for all rows that are already in the table; it seems that the AutoIncrement is only triggered for new rows that are added after this column has been added. Is there a way to set autonumber values for the rows that already exist?

Upvotes: 5

Views: 17289

Answers (4)

Mark Kram
Mark Kram

Reputation: 5832

I made a change to @Programnik solution.

DataTable dt = LoadDataTable();
using (DbDataReader dr = dt.CreateDataReader())
{
    //Get Original Datatable structure
    dt = dt.Clone();

    //Add Auto Increment Column called ID
    dt.Columns.Add(new DataColumn("ID")
    {
        AutoIncrement = true,
        AllowDBNull = false,
        AutoIncrementSeed = 1,
        AutoIncrementStep = 1,
        DataType = typeof(System.Int32),
        Unique = true
    });

    //Change Auto Increment Column Ordinal Position to 0 (i.e. First Column)
    dt.Columns["ID"].SetOrdinal(0);

    //Re-load original Data
    dt.Load(dr);
}

Upvotes: 2

Hack.Sign
Hack.Sign

Reputation: 57

This worked for me I was trying to get the unique values from another table and have them have a new ID.

        DataTable FinalNest = new DataTable();
        FinalNest.Columns.Add(new DataColumn("CuttingPlan", typeof(int)) { AutoIncrement = true, AutoIncrementSeed = 1, AutoIncrementStep = 1 });
        FinalNest.Columns.Add("Material", typeof(string));
        FinalNest.Columns.Add("IncludedPartIDs", typeof(string));
        DataTableReader dr = cutPlan.DefaultView.ToTable(true, "Material", "IncludedPartIDs").CreateDataReader();
        FinalNest.Load(dr);

Upvotes: 0

Programnik
Programnik

Reputation: 1555

I think there is an easier way which doesn't require looping through all the rows. There is a method on Datatable called CreateDataReader. So, clone your original datatable, add the identity column, create a datareader from the original table, then load the cloned table with the data reader. This will generate numbers in the identity column, eg

// original data table
DataTable origDT;

// create a reader
DataReader dr = origDT.CreatDataReader();

//clone original
DataTable clonedDT  = origDT.Clone();

//add identity column
clonedDT.Columns.Add(new DataColumn(){AutoIncrement=true});

//load clone from reader, identity col will auto-populate with values
clonedDT.Load(dr);

Upvotes: 1

Tim Schmelter
Tim Schmelter

Reputation: 460158

I don't think that it's possible to trigger the AutoIncrement functionality when the rows are already in the table. But you could update the table manually easily:

public void AddAutoIncrementColumn(DataTable dt)
{
    DataColumn column = new DataColumn();
    column.DataType = System.Type.GetType("System.Int32");
    column.AutoIncrement = true;
    column.AutoIncrementSeed = 0;
    column.AutoIncrementStep = 1;
    dt.Columns.Add(column);
    int index = -1;
    foreach (DataRow row in dt.Rows)
    {
        row.SetField(column, ++index);
    }
}

Upvotes: 11

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