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C# - Join Syntax with two tables [duplicate]

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}

How to write LINQ for multiple joins involving self join?

I am trying to translate the following query with self join to a LINQ expression.
select r2.* from depends d
join request r on d.DESC =r.DESC
join request r2 on d.ID=r2.ID
and d.TYPE ='sometype'
where r.ID= 12345
How can I correct the following LINQ query to match the correct SQL query above?
var result = (from d in depends
join r in request on d.DESC equals r.DESC
join r2 in request on d.ID == r2.ID && d.TYPE == incomingType.ToString()
where r.ID == incomingId
select r2).AsEnumerable();

Why don't you simple use a Where clause if your incomingType is fixed?
Also there is syntax for multiple join conditions, as shown here: LINQ Joining in C# with multiple conditions
E.g.:
var result = (from d in depends
where d.TYPE == incomingType.ToString()
join r in request on
new { ID = r.ID, desc = r.DESC }
equals
new { ID = d.ID, desc = d.DESC }
where r.ID == incomingId
select r).AsEnumerable();
If your incomingType is not actually fixed, and it gets its value from the depends table, you can just add a third parameter to the join condition, e.g.
var result = (from d in depends
where d.TYPE == incomingType.ToString()
join r in request on
new { ID = r.ID, desc = r.DESC, type = r.someType1 }
equals
new { ID = d.ID, desc = d.DESC, type = d.someType2 }
where r.ID == incomingId
select r).AsEnumerable();

Linq EF group by to get latest entries into list of objects

I am trying to move from simple SQL to EF.
But there are some complex queries(joins) that it seems to hard to generate the linq for.
At first I tried to use sqltolinq tool to generate the linq but it gives error as some of the things are not supported in the query.
here is the linq:
var entryPoint = (from ep in dbContext.tbl_EntryPoint
join e in dbContext.tbl_Entry on ep.EID equals e.EID
join t in dbContext.tbl_Title on e.TID equals t.TID
where e.OwnerID == user.UID
select new {
UID = e.OwnerID,
TID = e.TID,
Title = t.Title,
EID = e.EID
});
The table entry has many entries that I would like to group and get the latest for each group. But then I would need to select into a view model object which will be bind to gridview.
I dont know where I can implement the logic to group by and get the latest from each and be able to get values from join table into viewModel object.
somewhere I need to add
group entry by new
{
entry.aID,
entry.bCode,
entry.Date,
entry.FCode
}
into groups
select groups.OrderByDescending(p => p.ID).First()
in the above linq to retrieve latest from each group.

You can insert group by right after the joins:
var query =
from ep in dbContext.tbl_EntryPoint
join e in dbContext.tbl_Entry on ep.EID equals e.EID
join t in dbContext.tbl_Title on e.TID equals t.TID
where e.OwnerID == user.UID
group new { ep, e, t } by new { e.aID, e.bCode, e.Date, e.FCode } into g
let r = g.OrderByDescending(x => x.e.ID).FirstOrDefault()
select new
{
UID = r.e.OwnerID,
TID = r.e.TID,
Title = r.t.Title,
EID = r.e.EID
};
The trick here is to include what you need after the grouping between group and by.
However, the above will be translated to CROSS APPLY with all joins included twice. If the grouping key contains fields from just one table, it could be better to perform the grouping/selecting the last grouping element first, and then join the result with the rest:
var query =
from e in (from e in dbContext.tbl_Entry
where e.OwnerID == user.UID
group e by new { e.aID, e.bCode, e.Date, e.FCode } into g
select g.OrderByDescending(e => e.ID).FirstOrDefault())
join ep in dbContext.tbl_EntryPoint on e.EID equals ep.EID
join t in dbContext.tbl_Title on e.TID equals t.TID
select new
{
UID = e.OwnerID,
TID = e.TID,
Title = t.Title,
EID = e.EID
};

Why don't my SQL results match my Linq results?

When I run this Query in SQL I get what I want:
SELECT Auckland_Park.Formative.[Formative Name]
FROM Auckland_Park.LearningUnit
INNER JOIN Auckland_Park.Formative
ON Auckland_Park.LearningUnit.ID = Auckland_Park.Formative.FK_LU
INNER JOIN Auckland_Park.Reference
INNER JOIN Auckland_Park.Course
ON Auckland_Park.Reference.FK_Course = Auckland_Park.Course.ID
ON Auckland_Park.LearningUnit.ID = Auckland_Park.Reference.FK_LU
WHERE Auckland_Park.Course.Name = 'BI'
My result:
Querying SQL Build
Report Develop
Java App Develop
Andriod App Set up
SharePoint Server
But when I work with my C# app I'm using LINQ to SQL, my LINQ Query looks like this:
//LINQ Query to fill Foramtive Name ComboBox
CTUDataContext data = new CTUDataContext();
var course = (from r in data.LearningUnits
join a in data.Formatives
on r.ID equals a.FK_LU
join f in data.References
on r.ID equals f.FK_LU
join g in data.Courses
on f.FK_LU equals g.ID
where g.Name == ("BI")
select new
{
formativeName = a.Formative_Name,
ID = a.ID
}
).ToList();
txtFormativeName.ItemsSource = course;
txtFormativeName.DisplayMemberPath = "formativeName";
txtFormativeName.SelectedValuePath = "ID";
It seems the same, but I'm not getting the same result that I'm getting with the SQL Query above.

//LINQ Query to fill Foramtive Name ComboBox
CTUDataContext data = new CTUDataContext();
var course = (from r in data.LearningUnits
join a in data.Formatives
on r.ID equals a.FK_LU
join f in data.References
on r.ID equals f.FK_LU
join g in data.Courses
on f.FK_LU equals g.ID
where g.Name == ("BI")
select new
{
formativeName = a.Formative_Name,
ID = a.ID
}
).ToList();
txtFormativeName.ItemsSource = course;
txtFormativeName.DisplayMemberPath = "formativeName";
txtFormativeName.SelectedValuePath = "ID";
ANSWER:
on f.FK_LU equals g.ID
f.FK_LU
must be replaced with
f.FK_Course

entityframework inner join

I am trying to join between customers,orders,orderdetails and products
I used the following to generate an inner join query
IQueryable<Customer> CustomerList = ent.Customer
.Include("orders").Include("orders.orderdetails")
.include(orders.orderdetails.products)
I need to generate an inner join with these tables so that i can check surname and firstname in where clause but it is generating left outer join.
How to generate an inner join with these tables
thanks

var query = from OrdersDetails od in ent.OrdersDetails
select new {
od.Orders.Customers.FirtsName,
od.Orders.OrderDate,
....
}
Hope it helps.

try this
var v = from en in context.Entity
let leftouter = (from pa in en.PostalAddress
select new
{
pa.PostalAddressID
}).FirstOrDefault()
select new
{
EntityID = en.EntityID,
PostalAddressID = (Guid?)leftouter.PostalAddressID,
};
refered from http://geekswithblogs.net/SudheersBlog/archive/2009/06/11/132758.aspx