I'm trying to create a Linq query for EF that joins on 2 values from an inner select. Underneath you will find the SQL query that does the trick, things are much more tricky when trying to do so in Linq.
I use POCO object and would like the query to return the List and not an anonymous type. Is this possible with Linq to EF?
SELECT s1.*
FROM [Statistics] s1
INNER JOIN
(
SELECT MAX(CreateDate) as createdate
FROM [Statistics]
GROUP BY UserId
) s2
ON s1.UserId = s2.[UserId] and s1.CreateDate = s2.createdate
ORDER BY s1.Balance desc
You can do this with a Where or a Join.
from s1 in Statistics
join s2 in (from s in Statistics group s by s.UserId into g
select new { UserId = g.Key, CreateDate = g.Max (s => s.CreateDate) })
on new { s1.UserId, s1.CreateDate } equals new { s2.UserId, s2.CreateDate }
orderby s1.Balance descending
select s1;
Or,
from s1 in Statistics
from s2 in (from s in Statistics group s by s.UserId into g
select new { UserId = g.Key, CreateDate = g.Max (s => s.CreateDate) })
where s1.UserId == s2.UserId && s1.CreateDate == s2.CreateDate
orderby s1.Balance descending
select s1;
Related
I want to make this query in linq to sql .
Please help. I am new to linq and having problem to with the group by clause .
Here is the sql query
select count(USERID), d.DEPTNAME from USERS u
join department d on u.DEPTID = d.DEPTID
group by u.DEPTID, d.DEPTNAME
A more direct translation would be like this:
var query =
from u in db.Users
join d in db.Departments on u.DeptId equals d.DeptId
group d by new { d.DeptId, d.DeptName } into g
select new
{
g.Key.DeptName,
Count = g.Count(),
};
Though I think it would be better off written like this:
// looks like we're counting users in each department
var query =
from d in db.Departments
select new
{
d.DeptName,
Count = db.Users.Count(u => u.DeptId == d.DeptId),
};
I want to join the following Tables
1. B_Book[1st Table]
-B_BID (Book ID)(PK)
-B_Name
-B_CategroyID (FK)
2. BI_BookInstance [2nd Table]
-BI_IID(Instance ID)
-BI_BID (FK)
-BI_Price
3. BC_BookCategory [3rd Table]
-BC_CategoryID (PK)
-BC_CategoryName
First Join B_Book and BI_BookInstance then join the result of those both with BookCategory.
(1st join)[B_BID equals BI_BID]
(2nd nested join)[result of 1st join B_CategoryID equals BC_CategoryID]
Edit
SQL would be something like the following:
SELECT * FROM
(SELECT * FROM B_Book b JOIN BI_BookInstance bi on b.B_BID = bi.BI_BID) as t1
JOIN BC_BookCategoryID bc on bc.BC_CategoryID = t1.B_CategoryID
What matches your query in LINQ would be the following (and you'll notice the similarity with SQL). I've also included some examples on how to rename the fields returned, such as Price or CategoryName:
var results = from b in B_Book
join bi in BI_BookInstance
on b.B_BID equals bi.BI_BID
join bc in BC_BookCategory
on b.B_CategoryID equals bc.BC_CategoryID
select new
{
// put in whatever fields you want returned here:
b.B_BID,
b.B_CategoryID,
b.B_Name,
bi.BI_BID,
bi.BI_IID,
Price = bi.BI_Price,
bc.BC_CategoryID,
CategoryName = bc.BC_CategoryName
};
I have supposed inner joins (your FKs is not null), so i would like query like this:
var ctx = new YourEntities();
var query = from b in ctx.B_Book
from bi in ctx.BI_BookInstance
from bc in ctx.BC_BookCategory
where b.B_BID == bi.BI_BID && b.B_CategoryID == bc.BC_CategoryID
select new
{
BInstID = bi.BI_IID,
BName = b.B_Name,
BPrice = bi.BI_Price,
BCategory = bc.BC_CategoryName
};
foreach (var item in query)
{
Console.WriteLine(item.BInstID);
Console.WriteLine(item.BName);
Console.WriteLine(item.BPrice);
Console.WriteLine(item.BCategory);
Console.WriteLine("");
}
You can do this without explicitly using linq's join statement, provided that navigation properties are in place:
from b in ctx.B_Book
from bi in b.BookInstances
select new { b.Property1, bi.Property2, b.BookCategory.Name }
I need to write Join statment after writing query in linq
example :
var Query = (from Tab in Db.Employees
select Tab)
as i have some cases to perform join operation so
i need to do it on this Query Query.Join(Join with another Table like Department); I need the Syntax
if (DeptID != -1){ Query.Join(Join with table Department where FkDeptID = DeptID); }
Consider the usage of join in the LINQ 'query syntax':
from t1 in db.Table1
join t2 in db.Table2 on t1.field equals t2.field
select new { t1.field2, t2.field3}
Something like this?
var results = (from q in Query
join m in myList on q.SomeID = m.SomeID
select unknown);
Try using this query:
var Query =
from e in Db.Employees
join d in Db.Departments on e.FkDeptID equals d.DeptID into departments
select new
{
Employee = e,
Department = departments.SingleOrDefault(),
};
This works assuming that when e.FkDeptID == -1 that there is no record in the Departments table and in that case Department would be assigned null.
You should never have more than one department for an employee so I've used SingleOrDefault rather than FirstOrDefault.
I have the following view:-
CREATE VIEW tbl_adjudicator_result_view
AS
SELECT a.adjudicator_id, sar.section_adjudicator_role_id, s.section_id, sdr.section_dance_role_id, d.dance_id, c.contact_id,
ro.round_id, r.result_id, c.title, c.first_name, c.last_name, d.name, r.value, ro.type
FROM tbl_adjudicator a
INNER JOIN tbl_section_adjudicator_role sar on sar.section_adjudicator_role2adjudicator = a.adjudicator_id
INNER JOIN tbl_section s on sar.section_adjudicator_role2section = s.section_id
INNER JOIN tbl_section_dance_role sdr on sdr.section_dance_role2section = s.section_id
INNER JOIN tbl_dance d on sdr.section_dance_role2dance = d.dance_id
INNER JOIN tbl_contact c on a.adjudicator2contact = c.contact_id
INNER JOIN tbl_round ro on ro.round2section = s.section_id
LEFT OUTER JOIN tbl_result r on r.result2adjudicator = a.adjudicator_id AND r.result2dance = d.dance_id
When I run the following query directly against the db I get 0 in the count column where there is no result
select adjudicator_id, first_name, COUNT(result_id)
from tbl_adjudicator_result_view arv
where arv.round_id = 16
group by adjudicator_id, first_name
However when I use LINQ query I always get 1 in the Count Column
var query = from arv in db.AdjudicatorResultViews
where arv.round_id == id
group arv by new { arv.adjudicator_id, arv.first_name} into grp
select new AdjudicatorResultViewGroupedByDance
{
AdjudicatorId = grp.Key.adjudicator_id,
FirstName = grp.Key.first_name,
Count = grp.Select(p => p.result_id).Distinct().Count()
};
What do I need to change in the View / Linq query.
You're not doing the same thing in the LINQ query as in the SQL. COUNT(result_id) does not count distinct values of result_id - it counts non-null values.
Try this instead:
Count = grp.Select(p => p.result_id).Where(x => x != null).Count()
The point is: you're grouping your data in the LINQ query - and you'll always get at least one group.
That group's Count may be 0 - but the count of groups will be 1.
How can I write a linq to entities query that includes a having clause?
For example:
SELECT State.Name, Count(*) FROM State
INNER JOIN StateOwner ON State.StateID = StateOwner.StateID
GROUP BY State.StateID
HAVING Count(*) > 1
Any reason not to just use a where clause on the result?
var query = from state in states
join stateowner in stateowners
on state.stateid equals stateowner.stateid
group state.Name by state.stateid into grouped
where grouped.Count() > 1
select new { Name = grouped.Key, grouped.Count() };
I believe you can use a GroupBy followed by a Where clause and it will translate it as a Having. Not entirely sure though.
If you want to compare a variable that is not in the group by (Ex: age), then it would be:
var duplicated = (
from q1 in db.table1
where (q1.age >= 10 )
group q1 by new { q1.firstName, q1.lastName } into grp
where (grp.Count() > 1 )
select new
{
firstName= grp.Key.firstName,
lastName = grp.Key.lastName,
}
);