How do i write linq query for below for each loop

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C#

List<GlobalFieldDatabase> fin = new List<GlobalFieldDatabase>();
          foreach(var t in bg){
                 if(UserEntites.ContainsKey(t.BudgetEntityCode)){
                     if (UserGlobalFields.ContainsKey(t.GlobalFieldCode))
                     {
                         GlobalFieldDatabase g = new GlobalFieldDatabase();
                         g.BudgetEntityId = UserEntites[t.BudgetEntityCode];
                         g.GlobalFieldId = UserGlobalFields[t.GlobalFieldCode];
                         g.GlobalFieldValue = t.GlobalFieldValue;
                         fin.Add(g);
                     }
                 }
                 }

What I have tried:

I have tried but couldn't accomplish the task wasted lots of time TIA

Posted 5-Mar-16 9:29am

MYQueries1

Updated 5-Mar-16 9:54am

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Sascha Lefèvre · Answer 1 · 2016-03-05T09:54:00

Solution 1

It's possible of course but it doesn't gain you much in terms of clarity or lines of code savings (and it also isn't faster, as LINQ isn't inherently faster than a conventional approach):

C#

List<GlobalFieldDatabase> fin =
    (from t in bg
     where UserEntites.ContainsKey(t.BudgetEntityCode)
     && UserGlobalFields.ContainsKey(t.GlobalFieldCode)
     select new GlobalFieldDatabase()
     {
         BudgetEntityId = UserEntites[t.BudgetEntityCode],
         GlobalFieldId = UserGlobalFields[t.GlobalFieldCode],
         GlobalFieldValue = t.GlobalFieldValue
     })
    .ToList();

Edit: By the above reservations I don't mean that I would advise against using LINQ here, just that there is no objective benefit and you'd have to decide yourself which approach to use based on personal preference.

Posted 5-Mar-16 9:54am

Sascha Lefèvre

Updated 5-Mar-16 10:56am

v2

Comments

MYQueries1 5-Mar-16 16:16pm

List<globalfielddatabase> fin =
(from t in bg.AsParallel()
where UserEntites.ContainsKey(t.BudgetEntityCode)
&& UserGlobalFields.ContainsKey(t.GlobalFieldCode)
select new GlobalFieldDatabase()
{
BudgetEntityId = UserEntites[t.BudgetEntityCode],
GlobalFieldId = UserGlobalFields[t.GlobalFieldCode],
GlobalFieldValue = t.GlobalFieldValue
})
.ToList();

Linq isn't faster then foreach approach?
I think i can use AsParallel() to acheive paralleism to the code u given

Sascha Lefèvre 5-Mar-16 16:21pm

> Linq isn't faster then foreach approach?
No, there's still "the same" foreach-loop happening, just "inside" of Linq.

> I think i can use AsParallel() to acheive paralleism to the code u given
That could potentially be faster, but not neccessarily, as the CLR dynamically decides whether parallelism will actually be used. You'd have to try it.

MYQueries1 5-Mar-16 16:33pm

I have datatable which contains columns A and Column B. How i can write linq query to match the datatable["A"]=BudgetEntityId and datatable["B"]=GlobalFieldId.
Bascially i want the rows from the datatable to match aganist the list of object fin.
How i can do that? foreach is better or LInq is better

Sascha Lefèvre 5-Mar-16 16:53pm

from row in dataTable.AsEnumerable()
where row.Field<int>("A") == BudgetEntityId
&& row.Field<int>("B") == GlobalFieldId
...

(change <int> to the required type if other than int)

I mostly choose between foreach (or other types of loops) and Linq in terms of code clarity - which obviously is a subjective matter.

MYQueries1 5-Mar-16 23:01pm

it should also iterate List fin all the matching rows from the datatable aganist the list fin . I need that result

MYQueries1 5-Mar-16 23:05pm

I have written some thing like this
var ttt= from row in dataTable.AsEnumerable()
join yy in fin on
row.Field<int>("A") equals yy.GlobalFieldId && row.Field<int>("A") equals yy.BudgetEntityId

Getting error as row not in the scope on the right side equals

Sascha Lefèvre 6-Mar-16 5:40am

The syntax gets a bit unusual at first sight when joining on more than one field in Linq:

join yy in fin on new {row.Field("A"), row.Field("B")} equals new {yy.GlobalFieldId, yy.BudgetEntityId}

MYQueries1 6-Mar-16 6:08am

var ttt= from row in ds.Tables[0].AsEnumerable()
join yy in fin on new { vv = row.Field<int>("A"), tttt = row.Field<int>("B") }
equals new {vv=yy.GlobalFieldId, tttt=yy.BudgetEntityId}

It not filtering out the records returning all records in the dataset. Any idea what i am doing wrong

Sascha Lefèvre 6-Mar-16 6:15am

Right - try this:

{ a = row.Field<int>("A"), b = row.Field<int>("B") } equals new { a = yy.GlobalFieldId, b = yy.BudgetEntityId }

Replace <int> by the appropriate type if other than int. Type members of the "anonymous types" (a and b here) have to be of the same type.

MYQueries1 6-Mar-16 6:20am

Tried the same still getting same result. I have also written another version of the query
This also returning same result. Any idea where i am doing wrong
var joinForUpdate = from rowA in ds.Tables[0].AsEnumerable()
where fin.Select(y => rowA.Field<int>("A") == y.BudgetEntityId && y.GlobalFieldId == rowA.Field<int>("B")).Any()
select rowA;

Sascha Lefèvre 6-Mar-16 6:28am

Are you sure that your DataTable actually contains rows that shouldn't match? Have you inspected it in debugging mode?

MYQueries1 6-Mar-16 6:31am

Yes. Above query compares the records in the datatable with list<fin>. there are only two matched records but returning the all records in the datatable

Sascha Lefèvre 6-Mar-16 6:57am

Can you show me the whole method?

MYQueries1 6-Mar-16 7:13am

List<globalfielddatabase> fin =
(from t in bg.AsParallel()
where UserEntites.ContainsKey(t.BudgetEntityCode)
&& UserGlobalFields.ContainsKey(t.GlobalFieldCode)
select new GlobalFieldDatabase()
{
BudgetEntityId = UserEntites[t.BudgetEntityCode],
GlobalFieldId = UserGlobalFields[t.GlobalFieldCode],
GlobalFieldValue = t.GlobalFieldValue
})
.ToList();
=========================================

var joinForUpdate = from rowA in ds.Tables[0].AsEnumerable()
where fin.Select(y => rowA.Field<int>("A") == y.BudgetEntityId && y.GlobalFieldId == rowA.Field<int>("B")).Any()
select rowA;

Sascha Lefèvre 6-Mar-16 7:53am

I don't see why it would return all rows of the table if there actually are non-matching rows. I know you said you already inspected the items in the list and the rows in the table while debugging but I'm assuming you're overlooking something there; I would suggest you inspect it again.
Just for debugging purposes you might try to limit the items in the list to one and then take a look at the rows in joinForUpdate:

List fin =
...
})
.First()
.ToList();