I was trying to do a sub query inside a left join using LINQ, it looks like this, in SQL:
SELECT fields
FROM table1 A
LEFT JOIN table2 B ON B.Establishment = A.Establishment
LEFT JOIN table3 C ON C.Vdb = B.Vdb AND C.Year = (SELECT MAX(Year) FROM table3 D WHERE D.Vdb = C.Vdb)
Using LINQ, I did the following:
var query = await (
from a in _context.Table1
join b in _context.Table2 on a.Establishment equals b.Establishment
join c0 in _context.Table3 on b.Vdb equals c0.Vdb into gGroup
from c in gGroup.Where(x => x.Year == (from c1 in _context.Table3
where c1.Vdb == x.Vdb
select c1.Year).Max()).DefaultIfEmpty()
select new
{
fields
})
.ToListAsync();
I built this code using LINQPad, so I was trying run there and everything was going fine, but when I put this code in my IDE and tried to run it I got the following error:
{
"Message": "The LINQ expression (expression here) could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.",
"ErrorName": "InvalidOperationException"
}
So I don't know exactly what's wrong so I can fix this, can anyone help me?
GroupJoin is almost non translatable by EF Core. Do not use this operator if you do not do simple LEFT JOIN.
I have rewritten query to use another technique which returns the same result:
var table3 = _context.Table3;
var latest =
from t in table3.Select(t => new { t.Vdb }).Distinct()
from r in table3
.Where(r => r.Vdb == t.Vdb)
.OrderByDescending(r.Year)
.Take(1)
select r;
var query =
from a in _context.Table1
join b in _context.Table2 on a.Establishment equals b.Establishment into gb
from b in gb.DefaultIfEmpty()
join c in latest on b.Vdb equals c.Vdb into gc
from c in gc.DefaultIfEmpty()
select new
{
// fields
};
Please note below is entirely made up for example sake. I have a similar query based on an sql code but couldn't translate it to LINQ to get correct value.
The sql basically looks like this:
select * from customers c
join proucts p on c.id = p.customerid
join credit r on r.customerid=c.id and ISNULL(r.trandate, c.registeredDate) >= c.registeredDate
I also tried to tweak the above sql and put the condition inside where and it also returns the same value I am getting in my #2 LINQ below(which is incorrect).
How can I use c (customer) inside .Where of credit? see code
1.
from c in customers
join p in products on c.id = p.customerid
join cr in credit.Where(r=> r.tranDate => c.registeredDate!=null?c.registeredDate : r.purchaseDate) on c.id=cr.customerid
...
2.
I know you would suggest why not just put it in a where below like below but I am getting incorrect value.
from c in customers
join p in products on c.id = p.customerid
join cr in credit on c.id=cr.customerid
where r.tranDate => c.registeredDate!=null?c.registeredDate : r.purchaseDate
Is there a workaround? I have tried tons of others but won't get me the correct one.
LINQ supports only equijoins. Any additional criteria should go to where clause. And yes, the other range variables are inaccessible from the join inner sequence, so the filtering should happen before or after the join.
So this SQL query:
select * from customers c
join products p on c.id = p.customerid
join credit r on r.customerid = c.id
and ISNULL(r.trandate, c.registeredDate) >= c.registeredDate
directly translates to this LINQ query:
from c in customers
join p in products on c.id equals p.customerid
join cr in credit on c.id equals cr.customerid
where (cr.tranDate ?? c.registeredDate) >= c.registeredDate
select new { c, p, cr };
Optionally, the condition
(cr.tranDate ?? c.registeredDate) >= c.registeredDate
can be replaced with
(cr.tranDate == null || cr.tranDate >= c.registeredDate)
List<ServicePacksDTO> allServicePacks = new List<ServicePacksDTO>();
using (var db = new DataContext())
{
allServicePacks=(
from sp in db.ServicePacks
join st in db.States.DefaultIfEmpty() on sp.State_id equals st.State_Id
join type in db.ServiceTypes on sp.ServiceType_Id equals type.ServiceType_Id
where
(type.ServiceType_desc.ToLower() == "accepted")
orderby sp.AustState_id
select sp.ToServicePacksDTO(db)).ToList();
}
The current code works fine, until I attempt to do an outer join on state. Is there away to do this easily?
Well firstly, you need to provide a bit more detail that "works fine, until i attempt to do xx".
What doesn't work? Is there an error? Unexpected results?
Forgetting about the DTO projection and db.ServiceTypes join, to do a LOJ between db.ServicePacks and db.States, do this:
var x = (from sp in db.ServicePacks
join st in db.States on sp.State_id equals st.State_id into spst
from x in spst.DefaultIfEmpty()
select new { /* fields */ }
).ToList();
Try that first, make sure that works (it should), and then add on your other join and projection.
I have a beginners LINQ2SQL question. I have this huge (but not complex) SQL statement:
SELECT Artikel.ArtikelID,
Artikel.CategorieID,
Artikel.ImageFile,
Artikel.RetailPrijs,
ISNULL(ShopArtikel.VerkoopsPrijs, Artikel.VerkoopsPrijs) AS VerkoopsPrijs,
Artikel.ArtikelCode,
Artikel.InAssortimentSinds,
ArtikelTaal.ArtikelNaam,
ArtikelTaal.ArtikelOmschrijving
FROM Artikel
INNER JOIN ArtikelTaal ON Artikel.ArtikelID = ArtikelTaal.ArtikelID
INNER JOIN ShopArtikel ON Artikel.ArtikelID = ShopArtikel.ArtikelID
INNER JOIN Categorie ON Artikel.CategorieID = Categorie.CategorieID
INNER JOIN CategorieTaal ON Categorie.CategorieID = CategorieTaal.CategorieID
INNER JOIN Shop ON ShopArtikel.ShopId = Shop.ShopID
INNER JOIN CategorieGroepShop ON Shop.ShopID = CategorieGroepShop.ShopId
INNER JOIN Taal ON ArtikelTaal.TaalCode = Taal.TaalCode AND CategorieTaal.TaalCode = Taal.TaalCode
INNER JOIN CategorieGroepTaal ON Taal.TaalCode = CategorieGroepTaal.TaalCode AND CategorieGroepShop.CategorieGroepId = CategorieGroepTaal.CategorieGroepID
INNER JOIN CategorieGroep ON Categorie.CategorieGroepID = CategorieGroep.CategorieGroepID AND CategorieGroepTaal.CategorieGroepID = CategorieGroep.CategorieGroepID AND CategorieGroepShop.CategorieGroepId = CategorieGroep.CategorieGroepID
WHERE (Shop.ShopID = 23) AND
(Taal.TaalCode = 'dut') AND
(Artikel.Onzichtbaar = 0) AND
(Artikel.NietBestelbaar = 0) AND
(Categorie.Onzichtbaar = 0) AND
(Artikel.Voorraad >= Artikel.LevertijdDrempel)
and I am converting this to LINQ and have this:
var allProducts = from artikelen in dc.Artikels
join sa in dc.ShopArtikels on artikelen.ArtikelID equals sa.ArtikelID
join at in dc.ArtikelTaals on artikelen.ArtikelID equals at.ArtikelID
join cat in dc.Categories on artikelen.CategorieID equals cat.CategorieID
join catt in dc.CategorieTaals on cat.CategorieID equals catt.CategorieID
join catg in dc.CategorieGroeps on cat.CategorieGroepID equals catg.CategorieGroepID
join catgt in dc.CategorieGroepTaals on catg.CategorieGroepID equals catgt.CategorieGroepID
join sh in dc.Shops on sa.ShopId equals sh.ShopID
join catgs in dc.CategorieGroepShops on sh.ShopID equals catgs.ShopId
join tl in dc.Taals on new { tc1 = at.TaalCode, tc2 = catgt.TaalCode } equals new { tc1 = tl.TaalCode, tc2 = tl.TaalCode }
where sh.ShopID == shop.BLL.Business.ShopController.CurrentShop.Id
select dc.Artikels;
but I have the idea that I made some (minor) mistakes while joining.
any ideas please!
EDIT
I have rewritten the LINQ query to this:
var allProducts = from artikelen in dc.Artikels
join at in dc.ArtikelTaals on artikelen.ArtikelID equals at.ArtikelID
join sa in dc.ShopArtikels on artikelen.ArtikelID equals sa.ArtikelID
join cat in dc.Categories on artikelen.CategorieID equals cat.CategorieID
join catt in dc.CategorieTaals on cat.CategorieID equals catt.CategorieID
join sh in dc.Shops on sa.ShopId equals sh.ShopID
join catgs in dc.CategorieGroepShops on sh.ShopID equals catgs.ShopId
join tl in dc.Taals on new { tc1 = at.TaalCode, tc2 = catt.TaalCode } equals new { tc1 = tl.TaalCode, tc2 = tl.TaalCode }
join catgt in dc.CategorieGroepTaals on new { tl.TaalCode, catgs.CategorieGroepId } equals new { catgt.TaalCode, catgt.CategorieGroepID }
join catg in dc.CategorieGroeps on new { cat.CategorieGroepID, catgt.CategorieGroepID, catgs.CategorieGroepId } equals new { catg.CategorieGroepID, catg.CategorieGroepID, catg.CategorieGroepID }
where sh.ShopID == 230
select dc.Artikels;
but I have a syntax error after "dut" }
Edit 2:
changed the join and replaced "dut" with the corresponding field in the database.
still have the error after the first }
it says: type inference failed in the call to 'Join'
Some of the SQL joins have multiple join conditions, which you didn't put in the LINQ query.
If this is something that will be frequently run then you should rewrite it as a stored procedure. I believe it is too convoluted and complex for a LINQ statement - too hard to see what's going on.
There is a tool for it, but I didn't try it. May be it's usefull for you.
http://www.sqltolinq.com/
It looks like the error line is actually a "Where" cause but not "Joining".
You can actually split the whole long Linq statement into smaller Query.
so for this case, its better to split it like this:
var at = from a in dc.ArtikelTaals
where a.TaalCode == "dut"
select a;
var catt = from c in dc.CategorieTaals
where c.TaalCode == "dut"
select c;
.....
and you can join the IQueryable "at" and "catt" in your complex query later.
I'm writing a LINQ to SQL statement, and I'm after the standard syntax for a normal inner join with an ON clause in C#.
How do you represent the following in LINQ to SQL:
select DealerContact.*
from Dealer
inner join DealerContact on Dealer.DealerID = DealerContact.DealerID
It goes something like:
from t1 in db.Table1
join t2 in db.Table2 on t1.field equals t2.field
select new { t1.field2, t2.field3}
It would be nice to have sensible names and fields for your tables for a better example. :)
Update
I think for your query this might be more appropriate:
var dealercontacts = from contact in DealerContact
join dealer in Dealer on contact.DealerId equals dealer.ID
select contact;
Since you are looking for the contacts, not the dealers.
And because I prefer the expression chain syntax, here is how you do it with that:
var dealerContracts = DealerContact.Join(Dealer,
contact => contact.DealerId,
dealer => dealer.DealerId,
(contact, dealer) => contact);
To extend the expression chain syntax answer by Clever Human:
If you wanted to do things (like filter or select) on fields from both tables being joined together -- instead on just one of those two tables -- you could create a new object in the lambda expression of the final parameter to the Join method incorporating both of those tables, for example:
var dealerInfo = DealerContact.Join(Dealer,
dc => dc.DealerId,
d => d.DealerId,
(dc, d) => new { DealerContact = dc, Dealer = d })
.Where(dc_d => dc_d.Dealer.FirstName == "Glenn"
&& dc_d.DealerContact.City == "Chicago")
.Select(dc_d => new {
dc_d.Dealer.DealerID,
dc_d.Dealer.FirstName,
dc_d.Dealer.LastName,
dc_d.DealerContact.City,
dc_d.DealerContact.State });
The interesting part is the lambda expression in line 4 of that example:
(dc, d) => new { DealerContact = dc, Dealer = d }
...where we construct a new anonymous-type object which has as properties the DealerContact and Dealer records, along with all of their fields.
We can then use fields from those records as we filter and select the results, as demonstrated by the remainder of the example, which uses dc_d as a name for the anonymous object we built which has both the DealerContact and Dealer records as its properties.
var results = from c in db.Companies
join cn in db.Countries on c.CountryID equals cn.ID
join ct in db.Cities on c.CityID equals ct.ID
join sect in db.Sectors on c.SectorID equals sect.ID
where (c.CountryID == cn.ID) && (c.CityID == ct.ID) && (c.SectorID == company.SectorID) && (company.SectorID == sect.ID)
select new { country = cn.Name, city = ct.Name, c.ID, c.Name, c.Address1, c.Address2, c.Address3, c.CountryID, c.CityID, c.Region, c.PostCode, c.Telephone, c.Website, c.SectorID, Status = (ContactStatus)c.StatusID, sector = sect.Name };
return results.ToList();
You create a foreign key, and LINQ-to-SQL creates navigation properties for you. Each Dealer will then have a collection of DealerContacts which you can select, filter, and manipulate.
from contact in dealer.DealerContacts select contact
or
context.Dealers.Select(d => d.DealerContacts)
If you're not using navigation properties, you're missing out one of the main benefits on LINQ-to-SQL - the part that maps the object graph.
Use Linq Join operator:
var q = from d in Dealer
join dc in DealerConact on d.DealerID equals dc.DealerID
select dc;
basically LINQ join operator provides no benefit for SQL. I.e. the following query
var r = from dealer in db.Dealers
from contact in db.DealerContact
where dealer.DealerID == contact.DealerID
select dealerContact;
will result in INNER JOIN in SQL
join is useful for IEnumerable<> because it is more efficient:
from contact in db.DealerContact
clause would be re-executed for every dealer
But for IQueryable<> it is not the case. Also join is less flexible.
Actually, often it is better not to join, in linq that is. When there are navigation properties a very succinct way to write your linq statement is:
from dealer in db.Dealers
from contact in dealer.DealerContacts
select new { whatever you need from dealer or contact }
It translates to a where clause:
SELECT <columns>
FROM Dealer, DealerContact
WHERE Dealer.DealerID = DealerContact.DealerID
Inner join two tables in linq C#
var result = from q1 in table1
join q2 in table2
on q1.Customer_Id equals q2.Customer_Id
select new { q1.Name, q1.Mobile, q2.Purchase, q2.Dates }
Use LINQ joins to perform Inner Join.
var employeeInfo = from emp in db.Employees
join dept in db.Departments
on emp.Eid equals dept.Eid
select new
{
emp.Ename,
dept.Dname,
emp.Elocation
};
Try this :
var data =(from t1 in dataContext.Table1 join
t2 in dataContext.Table2 on
t1.field equals t2.field
orderby t1.Id select t1).ToList();
OperationDataContext odDataContext = new OperationDataContext();
var studentInfo = from student in odDataContext.STUDENTs
join course in odDataContext.COURSEs
on student.course_id equals course.course_id
select new { student.student_name, student.student_city, course.course_name, course.course_desc };
Where student and course tables have primary key and foreign key relationship
try instead this,
var dealer = from d in Dealer
join dc in DealerContact on d.DealerID equals dc.DealerID
select d;
var Data= (from dealer in Dealer join dealercontact in DealerContact on dealer.ID equals dealercontact.DealerID
select new{
dealer.Id,
dealercontact.ContactName
}).ToList();
var data=(from t in db.your tableName(t1)
join s in db.yourothertablename(t2) on t1.fieldname equals t2.feldname
(where condtion)).tolist();
var list = (from u in db.Users join c in db.Customers on u.CustomerId equals c.CustomerId where u.Username == username
select new {u.UserId, u.CustomerId, u.ClientId, u.RoleId, u.Username, u.Email, u.Password, u.Salt, u.Hint1, u.Hint2, u.Hint3, u.Locked, u.Active,c.ProfilePic}).First();
Write table names you want, and initialize the select to get the result of fields.
from d1 in DealerContrac join d2 in DealerContrac on d1.dealearid equals d2.dealerid select new {dealercontract.*}
One Best example
Table Names : TBL_Emp and TBL_Dep
var result = from emp in TBL_Emp join dep in TBL_Dep on emp.id=dep.id
select new
{
emp.Name;
emp.Address
dep.Department_Name
}
foreach(char item in result)
{ // to do}