EF Core: how to load a single item from collection-nav property? - asp.net

Question

I have one-to-many relationship between two entities: User (one) has Messages (many) collection.
There needs to display some information about User and at the same time needs to load single Message.
I try to do something like:
mycontext.Users.Where(..).Include(user => user.Messages.Take(1).First());
However this code throws ecxeption
InvalidOperationException: The property expression 'user=> {from
Message m in [chat].Messages select
[m] => Take(1) => First()}' is not valid. The expression should
represent a property access: 't => t.MyProperty'. For more information
on including related data, see
http://go.microsoft.com/fwlink/?LinkID=746393.
How can I solve it?

Answer 1

Pretty easy. Instead of trying to load a message from a user, load the user from the message:
mycontext.Messages.Where(..).Include(msg => msg.User);
In fact, you can do it easier for you:
mycontext.Messages
.Include(msg => msg.User)
.Where(msg => msg.User...);
So you don't have to filter on Message rather than on User

Answer 2

You cannot do that the way you have tried.You have to retrieve all the related messages from the db and after that filter it on the memory (IEnumerable) as shown below.
var useList= mycontext.Users.Where(..).Include(user => user.Messages);
foreach (var u in useList)
{
var message= u.Messages.Take(1).First();
}