How can I fix linq query to select count of ids with group by? - entity-framework

Question

I want to create this SQL query to linq:
SELECT
COUNT(m.FromUserId) AS Messages,
m.FromUserId AS UserId
FROM
dbo.ChatMessages m
INNER JOIN
dbo.ChatMessagesRead mr ON mr.ChatMessageId = m.ChatMessageId
WHERE
m.ToUserId = #toUserId
GROUP BY
m.FromUserId
I have tried create following linq query:
var messages = from m in _dbContext.ChatMessages
join mread in _dbContext.ChatMessagesRead on m.ChatMessageId equals mread.ChatMessageId
where m.ToUserId == userId
group m by m.FromUserId into g
select new
{
UserId = g.Key,
Messages = g.Count()
};
var messagesList = messages.ToList();
But this doesn't work.
How can I fix this linq query?
I get this exception:
Expression of type 'System.Func2[Microsoft.Data.Entity.Query.EntityQueryModelVisitor+TransparentIdentifier2[Project.BL.ChatMessages.ChatMessages,Project.BL.ChatMessages.ChatMessagesRead],System.Int32]' cannot be used for parameter of type 'System.Func2[<>f__AnonymousType12[Project.BL.ChatMessages.ChatMessages,Project.BL.ChatMessages.ChatMessagesRead],System.Int32]' of method 'System.Collections.Generic.IEnumerable1[System.Linq.IGrouping2[System.Int32,Project.BL.ChatMessages.ChatMessages]] _GroupBy[<>f__AnonymousType12,Int32,ChatMessages](System.Collections.Generic.IEnumerable1[<>f__AnonymousType12[Project.BL.ChatMessages.ChatMessages,Project.BL.ChatMessages.ChatMessagesRead]], System.Func2[<>f__AnonymousType12[Project.BL.ChatMessages.ChatMessages,Project.BL.ChatMessages.ChatMessagesRead],System.Int32], System.Func2[<>f__AnonymousType1`2[Project.BL.ChatMessages.ChatMessages,Project.BL.ChatMessages.ChatMessagesRead],Project.BL.ChatMessages.ChatMessages])'"

Answer 1

I'm facing the same issue and I've found that there is an opened issue on the Entity Framework Core bugtracker
The only workaround for now seems to split the request in two.
var filtered = (from m in _dbContext.ChatMessages
join mread in _dbContext.ChatMessagesRead on m.ChatMessageId equals mread.ChatMessageId
where m.ToUserId == userId
select m).ToList();
var messages = from m in filtered
group m by m.FromUserId into g
select new
{
UserId = g.Key,
Messages = g.Count()
};

Answer 2

you can try this
var res = ctx.MyTable // Start with your table
.GroupBy(r => r.id) / Group by the key of your choice
.Select( g => new {Id = g.Key, Count = g.Count()}) // Create an anonymous type w/results
.ToList(); // Convert the results to List

Answer 3

Your code should work. However I created another version of your query using extension methods.
var messages =
_dbContext
.ChatMessages
.Where(message => message.ToUserId == userId)
.Join(
_dbContext.ChatMessageRead,
message => message.ChatMessageId,
readMessage => readMessage.ChatMessageId,
(m, mr) => m.FromUserId
)
.GroupBy(id => id)
.Select(group =>
new
{
UserId = group.Key,
Messages = group.Count()
}
);
Could you please try it if it also throws the same exception or not?