Develop Reference

Multiple table join with multiple table where clause

I have a query that's something like this.
Select a.*
from table1 a
inner join table2 b on a.field1 = b.field1
inner join table3 c on b.field2 = c.field2
where b.field4 = beta and c.field5 = gamma.
On LINQ, I tried to do that this way:
var query = (from a in table1
join b in table2 on a["field1"] equals b["field1"]
join c in table3 on b["field2"] equals c["field2"]
where (b["field4"] == beta && c["field5"] == gamma)
select a).ToList();
But for some reason, when I try to do this I get an error that says that the entity "table2" doesn't have the field Name = "field5", as though as the where clause was all about the last joined table and the other ones were unaccessible. Furthermore, the compiler doesn't seem to notice neither, because it lets me write c["field5"] == gamma with no warning.
Any ideas? Am I writing this wrong?
Thanks

See these links:
How to: Perform Inner Joins (C# Programming Guide)
What is the syntax for an inner join in linq to sql?
Why you don't create View in database, and Select your data from View in LINQ?

translate postgres sql to linq. Is it possible?

I need translate next sql to linq is it possible? That will have approximately the same speed
SELECT Count(tblcollectionimage.lngimageid),
tblcollectiontree.lngcollectionid,
tblcollection.txtname
FROM (tblcollectiontree
LEFT JOIN tblcollectionimage
ON blcollectiontree.lngcollectionid =
tblcollectionimage.lngcollectionid)
JOIN tblcollection
ON tblcollectiontree.lngcollectionid = tblcollection.lngcollectionid
WHERE lngcollectionparentid = 0
GROUP BY tblcollectiontree.lngcollectionid,
tblcollection.txtname
I have currently such linq but it doesn't work.
var results =(from collection in dataBase.tblcollections
join collectionTree in dataBase.tblcollectiontrees on
collection.lngcollectionid equals collectionTree.lngcollectionid
into generalCollections
from generalCollection in generalCollections
join images in dataBase.tblcollectionimages on
collection.lngcollectionid equals images.lngcollectionid
into generalCollectionImages
from generalCollectionImage in
generalCollectionImages.DefaultIfEmpty()
group generalCollectionImage by
generalCollectionImage.lngcollectionid into hello
from hellos in hello.DefaultIfEmpty()
join collection in dataBase.tblcollections on
hello.Key equals collection.lngcollectionid
select new
{
id = hello.Key,
name = hello.Count()
}).ToList();

Linq to SQL Query with fk

I try to realize this query from T-SQL in Linq to SQL:
Select * from RPG r
join RPGPlayer e on r.RPGID = e.RPGID
join [User] i on e.UserID = i.UserID
where i.Username like '%Dunkel%'
The result is correct for 2 Rows on SQL-Query itself.
I try this:
rpgList.Where(y => y.RPGPlayers == y.RPGPlayers.Where(e => e.User.Username.Contains(player))).ToList();
(rpgList is a list of the complete table loaded before)

Not entirely sure regarding the question, but the following is my attempt to represent the SQL join statement in LINQ …
from r in RPG
join e in RPGPlayer on r.RPGID equals e.RPGID
join i in User on e.UserID equals i.UserID
where i.Username.Contains("Dunkel")

Select from multiple tables using linq

I am trying to execute the following SQL statement using linq:
SELECT TTT.SomeField
FROM Table1 as T, Table2 as TT, Table3 as TTT
WHERE (T.NumberID = 100 OR T.NumberID = 101)
AND T.QuestionID = 200
AND T.ResponseID = TT.ResponseID
AND TT.AnswerID = TTT.AnswerID
Essentially getting one field from a third table based on primary/foreign key relationships to the other 2 tables. It is expected to have a single result every time.

var query = from t in db.Table1
join tt in db.Table2 on t.ResponseID equals tt.ResponseID
join ttt in db.Table3 on tt.AnswerID equals ttt.AnswerID
where (t.NumberID == 100 || t.NumberID == 101) && t.QuestionID == 200
select ttt.SomeField
If you always expect single result, you can wrap this in ().Single(), or, if there might be no results found, in ().SingleOrDefault().

If I understand you correct. You should read something about Joins I guess.
here

Inner join using LINQ on DataTables

I have these 2 DataTables, customerTableDT and customerAliasesTableDT. They are both populated from a database like this:
customerTableDT = UtilityDataAndFunctions.PerformDBReadTransactionDataTableFormat(String.Format("SELECT * FROM {0}", TableNames.customers));
customerAliasesTableDT = UtilityDataAndFunctions.PerformDBReadTransactionDataTableFormat(String.Format("SELECT * FROM {0}", TableNames.customerAliases));
Now I'm trying to do an inner join on the two datatables like this:
var customerNames = from customers in customerTableDT.AsEnumerable()
join aliases in customerAliasesTableDT.AsEnumerable on customers.Field<int>("CustomerID") equals aliases.Field<int>("CustomerID")
where aliases.Field<string>("Alias").Contains(iString) select customers.Field<string>("Name")
But it gives me this error:
The type of one of the expressions in the join clause is incorrect. Type inference failed in the call to 'Join'.
If I had to write in SQL about what I'm trying to do, its very simple:
SELECT * FROM CUSTOMERS C
INNER JOIN CustomerAliases ALIASES ON ALIASES.CustomerID = C.CustomerID
WHERE CA.Alias LIKE %STRING_HERE%
Any help ?

You missed brackets after AsEnumerable, so it's treated as Method Group, not IEnumerable<DataRow>:
var customerNames = from customers in customerTableDT.AsEnumerable()
join aliases in customerAliasesTableDT.AsEnumerable() on customers.Field<int>("CustomerID") equals aliases.Field<int>("CustomerID")
where aliases.Field<string>("Alias").Contains(iString) select customers.Field<string>("Name")