Entity Framework: String concat in database query - entity-framework

Question

I need to create a string concatenation with an linq statement. I have the following data:
Section
Id: 1, Title: Test1
Id: 2, Title: Test2
Section_User
SectionId: 1, UserId: 1
SectionId: 1, UserId: 2
Users
Id: 1, Name: User1
Id: 2, Name: User2
I need the following result:
SectionId: 1, Users: User1, User2
I create the following Linq statement:
var query2 = from section in this.context.Sections
from users in section.Users
group section by section2.Id into groupedSection
select new {
SectionId = groupedSection.Key,
Users = string.Join(",", users.Select (x => x.Name)) // compile error, but I don't know how I write the statement correctly
};
Could someone tell me, how I can create a string concatenation on database side (not in-memory) with an linq statement.
Thanks!!

Answer 1

Based on #Alexei 's link in the comments, your line should look like
var query2 = from section in this.context.Sections
from users in section.Users
group section by section2.Id into groupedSection
select new {
SectionId = groupedSection.Key,
Users = string.Join(",", (from u in users select s.Name).ToArray())
};
However, if that doesn't work due to LINQ to Entities error, and you're willing to simply leave Users as an IEnumerable<string>, you can simply use:
var query2 = from section in this.context.Sections
from users in section.Users
group section by section2.Id into groupedSection
select new {
SectionId = groupedSection.Key,
Users = (from u in users select s.Name)
};
And later whenever needed, you can join the strings, or display the names using a loop.