如何将SQL运算符转换为LINQ“ IN”联接

Question

I have this SQL statement:

Select Id from dbo.AspNetUsers users Join AspNetUserRoles roles On roles.RoleId in ('2', '4', '5')

which I would like to convert to Linq.

The closest I could get to it was:

from users in db.AspNetUsers
join roles in db.AspNetUserRoles on new { RoleId = "2" } equals new { RoleId = roles.RoleId }
select new users.Id

which only joins on RoleId = "2" , but I need it to join on RoleId = "4" and "5" as well. Apparently the "in" keyword is not supported within a join statement in LINQ.

Is there a way to achieve equivalent behaviour in LINQ, possibly using different function syntax?

Answer 1

Rather than using a JOIN, use a WHERE on the navigation property.

I'll leave comments inline as it should be easier to understand.

string[] roles = new[] { "2", "4", "5" };
var users = db.AspNetUsers
    // for each user
    .Where(user => user.Roles // get the roles
        // select the role id
        .Select(role => role.RoleId)
        // and filter by the wanted roles
        .Where(role => roles.Contains(role))
        // by ensuring any role with one of the wanted IDs exist
        .Any())
    // and then get the IDs of those users
    .Select(user => user.UserId)
    // to finally execute the query
    .ToList();