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C# Linq Table query to count the non-matching entries

I am quite new to this, I am running two SQL queries and I am creating two separate data tables, DataTable1 and DataTable2.
I am applying some linq criteria to DataTable1 and creating another data table from that, which is DataTable3.
var Query3 = from table1 in DataTable1.AsEnumerable()
where table1.Field<DateTime>("DateTime") <= Yday
where table1.Field<string>("StockCode").Contains("-CA") && !(table1.Field<string>("StockCode").Contains("-CAB")) ||
table1.Field<string>("StockCode").Contains("-CM") ||
table1.Field<string>("StockCode").Contains("-LP")
select table1;
DataTable DataTable3 = Query3.CopyToDataTable()
Now I would write another query to do the following.
Both data tables have a column JobNumber. I would like to query DataTable3 in DataTable 2 to count the rows that have similar JobNumber entries. Below is what I am doing but I am not getting the correct count.
int count = (from table3 in DataTable3.AsEnumerable()
join table2 in DataTable2.AsEnumerable() on table2.Field<string>("JobNumber") equals table3.Field<string>("JobNumber")
where table2.Field<string>("JobNumber") == table3.Field<string>("JobNumber")
select table2).Count();

You are creating a cartesian join and counting its result, was that what you indented ? Also in your linq your Join expression and where expression is same (where is redundant). It is not clear what you really want to count. Probably you instead wanted to count those in DataTable2 where JobNumbers exists in DataTable3?:
var jobNumbers = (from r in DataTable3.AsEnumerable()
select r.Field<string>("JobNumber")).ToList();
var count = (from r in DataTable2.AsEnumerable()
where jobNumbers.Contains( r.Field<string>("JobNumber") )
select r).Count();
As a side note, it would be much easier if you used Linq To SQL instead (rather than Linq To DataSet).

Join two tables with key in common and show on a datagrid c# linq

I need to join the two tables of a DataGrid, but I only want the values with the same id (idviagem is pk in table idviagem and is fk in table idpassageiro)
I don't know how to do the query, in that moment I only take the table tbpassageiro on the grid, and I want to join them on DataGrid when the keys are equals
using (checkinEntities1 db = new checkinEntities1())
{
var qcheckin = (from c in db.tbpassageiro
join g in db.tbviagem on c.idviagem equals g.idviagem
where c.idviagem == g.idviagem
select c).ToList();
gridpass.ItemsSource = qcheckin;
}
The binding I know 100% is correct (some values from table passageiro and the other Biding values from table tbviagem)
This what I want to do:

If you want columns from both tables, then you have to create a view model for the columns which you want from both tables.
using (checkinEntities1 db = new checkinEntities1())
{
var qcheckin = (from c in db.tbpassageiro
join g in db.tbviagem on c.idviagem equals g.idviagem
where c.idviagem == g.idviagem
select new viewModelName()
{
//get the column values here like
Hora = c.Hora,
Partida = g.Partida
}).ToList();
gridpass.ItemsSource = qcheckin;
}
Hope this will give you the answer you are looking for.

getting non matched values from two Datatable

Is there any direct method for getting non matched values from two data table. I have one datatable which returns all the groups from Active Directory, and another datatable consist of all the group names from sharepoint list. But i need the non matched values by comparing these two datatables. please help me, if it possible.
Thanks in advance.

You could use DataRowComparer to compare the rows.
For instance, to compare the first rows of 2 data tables:
DataRow left = table1.Rows[0];
DataRow right = table2.Rows[0];
IEqualityComparer<DataRow> comparer = DataRowComparer.Default;
bool bEqual = comparer.Equals(left, right);

You can use .Except to do this. (Assuming an ID column)
IEnumerable<int> idsInDataTableA = dataTableA.AsEnumerable().Select(row => (int)row["ID"]);
IEnumerable<int> idsInDataTableB = dataTableB.AsEnumerable().Select(row => (int)row["ID"]);
IEnumerable<int> difference = idsInDataTableA.Except(idsInDataTableB );

I want compare DataTable1 that not exist in DataTable2
You can use Linq. Very efficient approaches are Enumerable.Except or Enumerable.Join(as LEFT OUTER JOIN) which are using sets:
var keyColRows = dt1.AsEnumerable()
.Select(r => r.Field<int>("KeyColumn")
.Except(dt2.AsEnumerable().Select(r2 => r2.Field<int>("KeyColumn"));
foreach(int inTable2Missing)
Console.WriteLine(inTable2Missing);
or the Join approach selecting the whole DataRow:
var rowsOnlyInDT1 = from r1 in dt1.AsEnumerable()
join r2 in dt2.AsEnumerable()
on r1.Field<int>("KeyColumn") equals r2.Field<int>("KeyColumn") into groupJoin
from subRow in groupJoin.DefaultIfEmpty()
where subRow == null
select r1;
Here you can use rowsOnlyInDT1.CopyToDataTable to create a new DataTable of the rows in table1 which are unique/new or use foreach to enumerate them.

Comparing two datatables through Linq

Hi I'm trying to compare two datatable through Linq. But I get this exception:
Specific cast is invalid
Please help me as I am new to Linq. This is the code I'm using:
var matched1 = from table1 in dtAvailableStores.AsEnumerable()
join table2 in dtControlStores.AsEnumerable()
on table1.Field<int>("STORE_NBR")
equals table2.Field<int>("STORE_NBR")
select table1;
Here STORE_NBR is a string value.

You can have a fairly good idea with this piece of code:
var qry1 = datatable1.AsEnumerable().Select(a => new { MobileNo = a["ID"].ToString() });
var qry2 = datatable2.AsEnumerable().Select(b => new { MobileNo = b["ID"].ToString() });
var exceptAB = qry1.Except(qry2);
DataTable dtMisMatch = (from a in datatable1.AsEnumerable() join ab in exceptAB on a["ID"].ToString() equals ab.MobileNo select a).CopyToDataTable();
References:
Compare two datatable using LINQ Query
Compare two DataTables for differences in C#?

This would happen if that field isn't actually an int.

DataTable Join using LINQ in C#

I am joining two data tables using LINQ this way:
DataTable targetTable = dataTable1.Clone();
var dt2Columns = dataTable2.Columns.OfType<DataColumn>().Select(dc =>
new DataColumn(dc.ColumnName, dc.DataType, dc.Expression, dc.ColumnMapping));
var dt2FinalColumns = from dc in dt2Columns.AsEnumerable()
where targetTable.Columns.Contains(dc.ColumnName) == false
select dc;
targetTable.Columns.AddRange(dt2FinalColumns.ToArray());
var rowData = from row1 in dataTable1.AsEnumerable()
join row2 in dataTable2.AsEnumerable()
on row1.Field<string>("keyCol") equals row2.Field<string>("keyCol")
select row1.ItemArray.Concat(row2.ItemArray.Where(r2 => row1.ItemArray.Contains(r2) == false)).ToArray();
foreach (object[] values in rowData)
targetTable.Rows.Add(values);
I am facing three issues here:
In case of row count is not same for two tables, I want to pass default value or assign empty string for values not found in other table. How do I achieve this ?
If I have multiple columns and need to compare with AND how is that possible ?
What if I have to join multiple tables in run time. Is there any way to generate dynamic LINQ ?

If both tables have the same primary-key DataTable.Merge will work:
dataTable1.Merge(dataTable2 ,false, MissingSchemaAction.Add);
This will merge the schema(columns) of both tables, joins rows which have the same primary-key and add the other rows.