Get difference between two data-tables according to one column

Question

I have the following scenario:

Table A that has 50 records and Table B that has 2 records.

I need to define a new table, say TableDiff which should contain 48 records from Table A that doesn't exist in Table B

My problem is that Table A and Table B are not identical but I have the field rowId which exists in both tables that I need to compare using it.

Answer 1

One way using Enumerable.Except and Enumerable.Join:

var aIDs = TableA.AsEnumerable().Select(r => r.Field<int>("RowID"));
var bIDs = TableB.AsEnumerable().Select(r => r.Field<int>("RowID"));
var diff = aIDs.Except(bIDs);
DataTable tblDiff = (from r in TableA.AsEnumerable()
                    join dId in diff on r.Field<int>("RowID") equals dId
                    select r).CopyToDataTable();

Here's the linq-to-objects "left-join"-approach:

DataTable tblDiff = (from rA in TableA.AsEnumerable()
                     join rB in TableB.AsEnumerable()
                     on rA.Field<int>("RowID") equals rB.Field<int>("RowID") into joinedRows
                     from ab in joinedRows.DefaultIfEmpty()
                     where ab == null
                     select rA).CopyToDataTable();