Question

I’m using ModelBuilder to map an existing database to POCOs. I have courses, students, and meetings. Here are the tables

CREATE TABLE Courses (
    CourseID int,
    Name string)

CREATE TABLE Students(
    StudentID int,
    Name string)

CREATE TABLE Courses_Students (
    CourseID int,
    StudentID int)

CREATE TABLE Meetings (
    MeetingID int,
    CourseID int,
    MeetDate datetime)

And the POCOs

public class Course {
        public int CourseID { get; set; }
        public string Name { get; set; }
        public virtual ICollection<CourseMeeting> Meetings { get; set; }
        public virtual ICollection<Student> Students { get; set; }
}
public class Student {
        public int StudentID { get; set; }
        public string Name { get; set; }
}
public class Meeting {
        public int MeetingID { get; set; }
        public int CourseID { get; set; }
        public DateTime MeetDate { get; set; }
}

The table mapping works great:

modelBuilder.Entity<Course>().MapSingleType().ToTable("Courses");
modelBuilder.Entity<Student>().MapSingleType().ToTable("Students");
modelBuilder.Entity<Meeting>().MapSingleType().ToTable("Meetings");

And the many-to-many mapping with a join table and without a navigation property works (i.e. there is no Students.Courses property specified on WithMany())

modelBuilder.Entity<Course>()
    .HasMany(c => c.Students)
    .WithMany()
    .Map(StoreTableName.FromString("Courses_Students"), 
        (c, s) => new { CourseID = c.CourseID, StudentID = s.StudentID});

But I’m having trouble mapping the other relationship that doesn’t have a join table. This obviously isn’t right:

modelBuilder.Entity<Course>().HasMany(c => c.Meetings).WithMany();

Because it wants a join table: Invalid object name 'dbo.Course_Meetings'. I can add a Course property to the Meeting object and then use

modelBuilder.Entity<Course>()
    .HasMany(c => c.Meetings)
    .WithOptional(m => m.Course)
    .HasConstraint((c, m) => c.CoursID == me.CourseID);

But I’d like to do this without the navigation property. Is this possible with EF4 and an existing database?

Answer 1

It’s assuming it needs the join table (and thus looking for it) because you haven’t mapped the property in the original declaration.

Try manually mapping the properties on the actual table like this..

public class Meeting {
        public int MeetingID { get; set; }
        public int CourseID { get; set; }
        public DateTime MeetDate { get; set; }

        public Course { get; set; }
}

and then configure it as follows:

modelBuilder.Entity<Meeting>(m => new {
        MeetingId = m.Meeting,
        MeetDate = m.MeetDate,
        CourseId = m.Course.Id
})
.HasRequired(m => m.Course)
.WithMany()