Hello gues I need help with convert an SQL query to linq EF

Question

1.00/5 (1 vote)

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this is the query
when i wrote it in Linq an error appear

select u.user_name ,max(l.last_action_date)
from Users u join system_log l on u.user_id = l.user_id
group by u.user_name

What I have tried:

the error in some case is
The specified LINQ expression contains references to queries that are associated with different contexts.

Posted 30-Apr-19 23:09pm

KhaledMohammad

Updated 29-Sep-19 18:49pm

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F-ES Sitecore 1-May-19 5:45am

You'll probably need to post the code you are using as that error doesn't sound like it is anything to do with your linq code.

2 solutions

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Christian Graus · Answer 1 · 2019-04-30T23:52:00

Solution 1

Here's how you do max:

c# - Using Linq to SQL, how do I find min and max of a column in a table? - Stack Overflow[^]

Here is how you group by:

var totalProdcuts = from o in ctx.Orders
                    join p in ctx.Products on o.ProductId equals p.Id
                    group o.NumberOf by p.Name into g
                    select new { ProductName = g.Key, TotalOrdered = g.Sum() };

Posted 30-Apr-19 23:52pm

Christian Graus

Comments

KhaledMohammad 1-May-19 6:08am

i can do it separately
but i need them together

Christian Graus 1-May-19 6:11am

The example has a sum. Replace it with Max.

KhaledMohammad 1-May-19 6:43am

The problem was to use two different dbcontext in the same linq
Now the problem has been solved by putting them in a list before doing linq
Thx

Christian Graus 1-May-19 16:54pm

yeah, that's what I would have said if the question had been clearer :)

Harsh.Shah.ifour · Answer 2 · 2019-09-29T18:49:00

Solution 2

Hi
Your SQL query will look like below in Linq:

var query = from u in Users
join i in system_log on
u.user_id equals i.user_id
group u by u.user_name into usernew
select new 
{
  username = usernew.Key
  last_action_date = g.Max( p => p.usernew.last_action_date)
}

Hope This will help you.
Thank you.

Posted 29-Sep-19 18:49pm

Harsh.Shah.ifour

Updated 29-Sep-19 18:50pm

v2