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}
My goal is to return a list of orders that only contain orderItems that are from a specific merchant. My current solution is to iterate through EVERY order, then through every order item and every listing. I imagine that is not the best practice, but I am having a hard time figuring out how to construct a single query to retrieve merchant specific orders.
I have 4 tables
Merchants(the id field being merchantID)
Orders(the id field is orderID)
orderItems(the id field is orderItemID, and FK listingID)
listings(the id field is listingID, and FK merchantID)
You can use .Any() to help you get to where you want:
var ordersFromMerchant = db.Orders
.Where(o => o.Items.Any(oi => oi.Listing.merchantID = 10);
I've made assumptions about the names of your navigation properties, but you should be able to adapt this if they don't match.
If you prefer the linq syntax, you can use:
var ordersFromMerchant = from o in db.Orders
join oi in db.orderItems on o.orderID equals oi.orderID
join l in db.listings on oi.listingID equals l.listingID
where l.merchantID = 10
select o;
I don't know your structure but something like this should work.
var query = from o in orders
join oi in orderItems on o.id equals io.orderID
join l in listings on oi.listingID equals l.id
where l.merchantID == merchantID
select o;
if checkbox chkAus checked :
if (chkAus.Checked)
{
vAdvanceSearchResults = (from t in vAdvanceSearchResults
join imp in _bDataContext.Imprints on t.ImprintID equals imp.ID
join cc in _bDataContext.CountryCodes on imp.CountryID equals cc.ID
where cc.Code.Contains("AU")
select t).Distinct();**
}
if chkAus and chkNz are checked
if (chkNz.Checked && chkAus.Checked)
{
vAdvanceSearchResults = (from t in vAdvanceSearchResults
join imp in _bDataContext.Imprints on t.ImprintID equals imp.ID
join cc in _bDataContext.CountryCodes on imp.CountryID equals cc.ID
where cc.Code.Contains("AU") || cc.Code.Contains("NZ")
select t).Distinct();
}
The condition on linq query changes as the checkboxes are checked.
where cc.Code.Contains("AU") || cc.Code.Contains("NZ")
I have nearly 10 checkboxes, and got stuck on how to write that many conditions.
Any help please.
for example if there is chkUS :
then the combination with chkAus,chkNz,chkUS checkboxes the linq query would change.
where cc.Code.Contains("AU") || cc.Code.Contains("NZ") || cc.Code.Contains("US")
Put all of them in a list and then do a if list.contains(cc.Code)
var a = new List<string>(){"AU","NZ","US"};
var linq = (from t in vAdvanceSearchResults
join imp in _bDataContext.Imprints on t.ImprintID equals imp.ID
join cc in _bDataContext.CountryCodes on imp.CountryID equals cc.ID
where a.Contains(cc.Code)
select t).Distinct();
Create a list of selected checkboxes first. Like this.
var selectedCountries = new List<string>();
if (chkAus.Checked) selectedCountries.Add("AU");
if (chkNz.Checked) selectedCountries.Add("NZ");
if (chkUs.Checked) selectedCountries.Add("US");
//... And so on
And then modify your linq query to check whether this list contains the code or not, I mean reversing the comparison is an answer. Make sure you remove if condition for this linq query.
vAdvanceSearchResults = (from t in vAdvanceSearchResults
join imp in _bDataContext.Imprints on t.ImprintID equals imp.ID
join cc in _bDataContext.CountryCodes on imp.CountryID equals cc.ID
where selectedCountries.Contains(cc.Code)
select t).Distinct();
This will fix your problem.
Hi i am trying to join two tables in c#. the join code is given below. The problem is that when there is null value for tourid in tb_abc then in will not include that row from tb_abc in the list.
return (from p in context.tb_abc
from o in context.tb_Second
where o.id==p.tourId
where p.driverId == driverId
select new abcBean
{
id=p.id,
name=o.name
}).ToList<abcBean>();
Can anyone tell me what i am doing wrong
You are not doing an inner join in that query. You are doing a cross join, its where you have two tables and join each record to every other record.
If you want to include rows that return null on one of the constraints you need a left outer join.
return (from p in tb_abc
join o in tb_Second on p.tourId equals o.id into po
where p.driverId == driverId
from subpo in po.DefaultIfEmpty()
select new abcBean
{
id=p.id,
name=(subpo == null ? String.Empty : subpo.Name)
}).ToList();
Consider these two sql statements:
The first a cross join:
select id, name
from tb_abc o,
tb_Second p
where
o.id = p.tourID
and p.driverID = #driverID
The second a left outer join:
select id, name
from tb_abc o
LEFT OUTER JOIN tb_Second p on o.id = p.tourID
where
p.driverId = #driverID
The second will give you one set of the records, that include the null value of o.id.
The first will give you something of a Cartesian product which you rarely want.
Linq's DefaultIfEmpty() puts the default value (null) into the record if it doesnt find a match for the one side, so it behaves like the left outer join.
you can use left outer join like
return (from p in context.tb_abc
join o in context.tb_Second on o.id==p.tourId into gt
where p.driverId == driverId
from subsecond in gt.DefaultIfEmpty()
select new abcBean
{
id=p.id,
name=(subsecond == null ? String.Empty : subsecond.Name)
}).ToList<abcBean>();
In a previous question I asked how I would get a Customers first Order, it was answered thus :
var minOrders = from customer in DataSet.Customers
let order = (from o in DataSet.Orders where o.CustomerId == customer.CustomerId
order by o.OrderTimestamp
select o).first()
select new {
customer.Name,
order.OrderAmount
});
This is great, but how do I include a Left Outer Join onto the above? That is, return all Customers even if they have no orders, so something like :
var minOrders = from customer in DataSet.Customers LEFT OUTER JOIN
let order = (from o in DataSet.Orders where o.CustomerId == customer.CustomerId
order by o.OrderTimestamp
select o).first()
select new {
customer.Name,
order.OrderAmount
});
I know, in hindsight I should of asked this at the same time..
Thanks, Joe
Firstly, using let to do the join like this isn't ideal in the first place. There's a join clause in LINQ for a reason :)
Left outer joins aren't specifically supported in LINQ, but you can fake them like this:
var minOrders = from customer in DataSet.Customers
join order in DataSet.Orders.OrderBy(o => o.OrderTimestamp)
on customer.CustomerId equals o.CustomerId
into customerOrders
let order = customerOrders.FirstOrDefault()
select new {
customer.Name,
OrderAmount = order == null ? 0m : order.OrderAmount
};
Usually a left outer join uses from foo in bar.DefaultIfEmpty instead of let foo = bar.FirstOrDefault() but in this case you're only after the first match anyway, hence the different approach.
I'm pretty sure this works logically - whether the SQL translation will work or not is a different matter.