SQL 到 LINQ 的内部连接转换和不同表上的过滤器

Question

What will the following query:

select (UserRoles.RoleID, UserRoles.UserID) from UserRoles  
    inner Join Roles on Roles.RolesID = UserRoles.RoleID 
    where Roles.RoleName = 'Seller' AND UserRoles.UserID =1

look like in Entity framework?

I tried this:

var check = from a in UserRole 
            join b in Role 
            on a.RoleID equals b.RoleID
            select new{RoleName ="seller"};

but it's wrong, could someone please guide me?

Answer 1

The verbatim conversion of the query (after removing the parents in SELECT )

select UserRoles.RoleID, UserRoles.UserID
from UserRoles  
inner Join Roles on Roles.RolesID = UserRoles.RoleID 
where Roles.RoleName = 'Seller' AND UserRoles.UserID =1;

Would be the following in query syntax, against your DbContext called context (and I've assumed the default plural naming convention of DbSets:)

var result = from a in context.UserRoles
             join b in context.Roles
             on a.RoleID equals b.RoleID
             where b.RoleName == "Seller" && a.UserId == 1
             select new {b.RoleID, a.UserID};

Where we join the tables and project out the two columns you wanted.

However, if you've defined the navigation property UserRole.Role in your EF Model, explicit joining isn't required, and much simpler would be (I've switched to lambda syntax):

var result = context.UserRoles
   .Where(ur => ur.UserID == 1 && ur.Role.Name == "Seller")
   .Select(ur => new {ur.RoleID, ur.UserID});

Again, projecting out just the two columns into an anonymous class. If you omit the final Select statement entirely, you'll get the full UserRole entity instance.