Best way add a new column with sequential numbering in an existing data table

问题

I have a non empty datatable . What is the best way to add another column to it that has sequential numbering starting from 1.

I tried the following code. But did not work.

DataColumn dc = new DataColumn("Col1");
dc.AutoIncrement = true;
dc.AutoIncrementSeed = 1;
dc.AutoIncrementStep = 1;       
dc.DataType = typeof(Int32);
dt.Columns.Add(dc);

Will setting any expression help in this scenario ?

Thanks in Advance

回答1:

I think you could achieve that by using a 2nd "helper" data table that would contain just an auto-increment field and then you populate/merge it with the existing data, something like this:

DataTable dtIncremented  = new DataTable(dt.TableName);
DataColumn dc            = new DataColumn("Col1");
dc.AutoIncrement         = true;
dc.AutoIncrementSeed     = 1;
dc.AutoIncrementStep     = 1;
dc.DataType              = typeof(Int32);    
dtIncremented.Columns.Add(dc);

dtIncremented.BeginLoadData();

DataTableReader dtReader = new DataTableReader(dt);
dtIncremented.Load(dtReader);

dtIncremented.EndLoadData();

And then you would just return dtIncremented table instead of the original dt. Not an elegant solution but should work.

回答2:

below code worked for me

Code is Edited

        // Added temp rows so that this solution can mimic actual requirement

        DataTable dt = new DataTable();
        DataColumn dc1 = new DataColumn("Col");
        dt.Columns.Add(dc1);

        for(int i=0;i<10;i++)
        {
            DataRow dr = dt.NewRow();
             dr["Col"] = i.ToString();
             dt.Rows.Add(dr);
        }


        // Added new column with Autoincrement, 

        DataColumn dc = new DataColumn("Col1"); 
        dc.AutoIncrement = true;
        dc.AutoIncrementSeed = 1;
        dc.DataType = typeof(Int32);

        // Handeled CollectionChanged event

        dt.Columns.CollectionChanged += new CollectionChangeEventHandler(Columns_CollectionChanged);
        dt.Columns.Add(dc);

        // After column added demostratation

        DataRow dr1 = dt.NewRow();
            dt.Rows.Add(dr1);



    void Columns_CollectionChanged(object sender, CollectionChangeEventArgs e)
    {
        DataColumn dc = (e.Element as DataColumn);
        if (dc != null && dc.AutoIncrement)
        {
            long i = dc.AutoIncrementSeed;
            foreach (DataRow drow in dc.Table.Rows)
            {
                drow[dc] = i;
                i++;
            }
        }
    }

回答3:

You'll have to build a whole new datatable for this and manually deep-copy each row one by one from the old table to the new. Sorry.

来源：https://stackoverflow.com/questions/4310791/best-way-add-a-new-column-with-sequential-numbering-in-an-existing-data-table

标签

.net

datatable

datacolumn