I have an example of a query like the following. I have two tables named product and category. But I want him to do the search by name, not by id.I did the join but I get the error like below.The part where I get the error "from p in context.Products".The error I received is Could not find an implementation of the query pattern for source type. 'Join' not found.
public List<Product> GetProductsByCategory(int categoryId)
{
using (var context= new NorthwindContext())
{
var query= from p in context.Products
join c in context.Categories on p.CategoryId equals c.CategoryId
select new
{
ProductName= p.ProductName,
QuantityPerUnits = p.QuantityPerUnit,
UnitPrice = p.UnitPrice,
UnitInStock = p.UnitsInStock,
Category = c.CategoryName
};
return query.ToList();
}
}
What is the reason for this error? How can I fix.
Try adding using statement for linq:
using System.Linq;
Lets say that I have following tables:
Student(id(pk), name)
Class(id(pk), name)
StudentClass(id(pk), studentId(fk), classId(fk))
Imagine as follows:
Student table contains:
(1,"John"), (2, "Mike"), (3,"Josh")
Class table contains:
(1,"Geography"), (2, "Math")
StudentClass table contains:
(`1, 1, 1),(2,2,2),(3,3,2)
Lets now assume that I have a StudentClassDTO class which contains
List<string> StudentNames
string ClassName
How can I by using using LINQ query get data into StudentClassDTO? Any help appreciated.
var data = from sc in context.GetStudentClasses
join s in context.GetStudents on sc.StudentId equals s.Id
join c in context.GetClass on sc.ClassId equals c.Id
select new StudentClassDTO
{
}
so it gets name and classname 3 seperate ones but I need if their classes are same it should have to combine them where it will be just one classname and 2 different students. So it should be like {john, Geography} and {[Mike, Josh], Math}
Solution
from c in classes
join sc in studentClasses on c.Id equals sc.ClassId
join s in student on sc.StudentId equals s.StudentId
group s by new {c.Name} into g
select new StudentClassDTO
{
ClassName = g.Key.Name,
StudentNames = g.Select(a=>a.Name).ToList()
};
I use code like this all the time to accomplish what you're trying to do (untested and using the C# 7.3 syntax).
var xs =
from s in ctx.students
join cs in ctx.student_classes on cs.student_id equals s.student_id
join c in ctx.classes on c.class_id equals cs.class_id
select new
{
s, c
}
var memo = new Dictionary<int, StudentClassDTO>(); //the key is class_id
foreach(var x in xs)
{
if(!memo.Contains(x.c.class_id, out var #class))
memo.Add(x.c.class_id, #class = new StudentClassDTO(x.c.class_name));
#class.Accept(s.student_name);
}
sealed class StudentClassDTO
{
readonly List<string> student_names;
public string ClassName { get; }
public IEnumerable<string> StudentNames => student_names;
public(string class_name)
{
ClassName = class_name;
}
public void Accept(string name) => student_names.Add(name);
}
Using the LINQ group join operator, you can get a collection of matching student classes, however your query needs to start from the Class table since you want one StudentClassDTO per class. Unfortunately you have to nest the join from student classes to students (an EF navigation property may do better) so this may generate multiple queries.
var data = from c in context.GetClass
join sc in context.GetStudentClasses on c.Id equals sc.ClassId into scj
select new StudentClassDTO {
ClassName = c.Name,
StudentNames = (from sc in scj
join s in context.GetStudents on sc.StudentId equals s.Id
select s.Name).ToList()
};
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}
Please anyone can help me to write this sql query into Linq. i have tried..
this is my sql query
select o.OrderID,o.Nature,o.Date,od.TotalPrice,os.OrderStatus,lo.FirstName,lo.EmailAddress,lo.PhoneNumber
from [dbo].[Order] o
inner join [dbo].[tbl_OrderDetails] od on od.OrderID = o.OrderID
inner join [dbo].[tbl_OrderHistory] oh on oh.OrderID = o.OrderID
inner join [dbo].[tbl_Login] lo on o.UserID = lo.UserID
inner join dbo.tbl_OrderStatus os on oh.OrderStatusID= os.OrderStatusID
group by o.OrderID,o.Nature,od.TotalPrice,o.Date,os.OrderStatus,lo.FirstName,lo.EmailAddress,lo.PhoneNumber
and this is my try
public override orderDetailModel orderDetails(int id)
{
var results = from o in obj.Orders
join od in obj.tbl_OrderDetails on o.OrderID equals od.OrderID
join oh in obj.tbl_OrderHistory on o.OrderID equals oh.OrderID
join l in obj.tbl_Login on o.UserID equals l.UserID
join os in obj.tbl_OrderStatus on oh.OrderStatusID equals os.OrderStatusID
where (od.OrderID == id)
group o by new { o.Nature, o.OrderID } into
select new orderDetailModel
{
OrderID = o.OrderID,
OrderStatus = os.OrderStatus,
Date = o.Date,
DeliveryNature = o.Nature,
EmailAddress = l.EmailAddress,
FirstName = l.FirstName,
PhoneNumber = l.PhoneNumber,
TotalPrice = od.TotalPrice
};
//group o by new {o.OrderID};
orderDetailModel data = (orderDetailModel)results.FirstOrDefault();
return data;
}
but this is wrong query its not working fine please help me
You need to correct the group by clause, like you have in the SQL query like this:-
group new { o, l } by new { o.OrderID,o.Nature,od.TotalPrice,o.Date,os.OrderStatus,
l.FirstName, l.EmailAddress,l.PhoneNumber } into g
select new orderDetailModel
{
OrderID = g.Key.OrderID,
OrderStatus = g.Key.OrderStatus,
Date = g.Key.Date,
..and so on
};
Since you need the grouping on two tables Order & tbl_Login you will have to first project them as anonymous type group new { o, l } then specify all the groupings and finally while projecting use Key to get the respective items.
I guess that actually, also the SQL query is not correct.
I would simply use a SELECT DISTINCT ... instead of Grouping all the columns.
Anyway, first thing to do:
Check if databases is designed correctly. As far as i can see, if you're joining the table with their Ids, i don't understand why you need to group all the data. If you have duplicates, maybe the error is in the Database design.
If you can't change your Database, or you are happy with it, then use the following LINQ approach:
var distinctKeys = allOrderDetails.Select(o => new { o.OrderID, o.Nature, o.TotalPrice, o.Date,o.OrderStatus,o.FirstName, o.EmailAddress,o.PhoneNumber }).Distinct();
var joined = from e in allOrderDetails
join d in distinctKeys
on new { o.OrderID, o.Nature,o.TotalPrice, o.Date,o.OrderStatus, o.FirstName, o.EmailAddress, o.PhoneNumber } equals d select e;
joined.ToList(); // gives you the distinct/grouped list
I need help on the LINQ query below, the join on multiple fields seems to work, but i get
"Invalid 'join' condition. An entity member is invoking an invalid
property or method."
I've already tried to swap the conditions on the join to no luck
(from o in orderSet
join opr in OrderProductSet on o.Id equals opr.OrderId.Id
join pri in ProductPricingSet on
new {BusinessUnitId = o.BusinessUnitId.Id, AccountId = o.Accountid.Id, ProductNameId = opr.ProductNameId.Id} equals
new {BusinessUnitId = pri.BusinessUnitId.Id, AccountId = pri.AccountId.Id, ProductNameId = pri.ProductId.Id}
where o.name.Equals("OE-000701")
select new {
o.name,
o.orderId,
opr.ProductNameId.Name,
opr.Quantity,
pri.Discount,
pri.FinalPrice
})