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}
I am using this LINQ to Entity:
var t1 = (from cn in contracts
join cl in client on cn.Id equals cl.Id
join so in siteObject on cn.Id equals so.ContractId
select new
{
siteObjId = so.Id,
clientId = cl.Id,
}).ToList();
t1 have this list:
Is there any elegant way using (for example LINQ) to create from the list above (t1), new list like that:
You could group by statement the items. For each item of result, you could concat the result group using string.Join(separator, collection) to get a result like 1,2,3. But, first, given you are using Linq To Entities, first, try to execute a simple query grouping values. For sample:
var groupResult = (from cn in contracts
join cl in client on cn.Id equals cl.Id
join so in siteObject on cn.Id equals so.ContractId
group cl by cl.Id into g
select new {
ClientId = g.Key,
Result = g
}).ToList();
And use Linq To Objects with the groupResult list, to join the values into a string, for sample:
var t1= (from item in groupResult
select new {
clientId = item.ClientId,
siteObjId = string.Join(",", item.ToList()),
});
You want the group by operator:
(from x in t1
group x b x.ClientId into g
select new
{
ClientId = g.Key,
ModelIds = g.ToList()
}).ToList()
I have one below SQL query, it is more complex having some GroupBy, Conditions, etc. which i skip here in post to make my question easy:
SELECT
SUBSTRING(TSL.ctg_name, 6, 100) AS 'TREKK', *
FROM Filteredctg_timbersettlementline AS TSL
INNER JOIN Filteredctg_timbersettlement AS TS
ON TSL.ctg_timbersettlementid = TS.ctg_timbersettlementid
LEFT JOIN FilteredNew_property AS P
ON TS.ctg_propertyid = P.new_propertyid
WHERE (TS.ctg_timbersettlementid = #TimberSettlementID) AND
(TSL.ctg_reportgroup = 'TREKK')
I tried below Linq:
var Trekks = (from ts in XrmContext.ctg_timbersettlementSet
join tsl in XrmContext.ctg_timbersettlementlineSet
on ts.Id equals tsl.ctg_timbersettlementid.Id
join p in XrmContext.New_propertySet
on ts.ctg_propertyid.Id equals p.New_propertyId
into temp
from p in temp.DefaultIfEmpty()
where ts.ctg_timbersettlementId == TimberSettlementGuid
where tsl.ctg_reportgroup == "TREKK"
select new
{
tsl.ctg_name,
ts.ctg_BasisAllocatedForestryFund,
}).ToList();
It throwing me an error:
The method 'GroupJoin' cannot follow the method 'Join' or is not supported. Try writing the query in terms of supported methods or call the 'AsEnumerable' or 'ToList' method before calling unsupported methods.
How can i achive LEFT JOIN?
To achieve a left join, you need to use an intermediary DefaultIfEmpty() :
var query = from c in db.Customers
join o in db.Orders
on c.CustomerID equals o.CustomerID into sr
from x in sr.DefaultIfEmpty()
select new {
CustomerID= c.CustomerID, ContactName=c.ContactName,
OrderID = x.OrderID == null ? -1 : x.OrderID};
I have this table structure:
I have this LINQ query:
var query = (from p in context.People.Include("PeopleClub").Include("PeopleClub.Club")
orderby p.Name
select p).ToList();
Is it possible to do something like this:
var query = (from p in context.People
.Include("PeopleClub")
.Include("PeopleClub.Club")
orderby p.Name, p.PeopleClub.DisplaySequence
select p).ToList();
Update: Using Entity Framework 4.0
Update 2: I give up. See this similar question for another approach. I ended up rewriting my query without the .Include().
Try by navigation properties:
using System.Data.Entity; // notice using
var q = from p in context.People
.Include(p => p.PeopleClub) // notice lambda instead of string
.Include(p => p.PeopleClub.Club) // you may not need that though
orderby p.FirstName, p.ClubPerson.DisplaySequence
select p;
or regular join:
var q = from p in db.People
join pc in db.PeopleClub on p.PersonID equals pc.PersonID
join c in db.Clubs on pc.ClubID equals c.ClubID
orderby p.FirstName, pc.DisplaySequence
select p;