Seeding Many-To-Many data

Question

Hello I'm trying to create some seeds for my project, but I'm having trouble seeding the Many-To-Many relationship data to the db.

My database looks like this:

in TeacherSkills, Teacher_ID and Skill_ID are foreign keys for their tables ofcourse.

My seeder looks like this

protected override void Seed(Ability_Examen_ASP.Models.AbilityDbContext context)
    {
        if (!context.Skills.Any())
        {
            context.Skills.Add(new Models.Skill { SkillName = "PHP" });
            context.Skills.Add(new Models.Skill { SkillName = "Java" });
            context.Skills.Add(new Models.Skill { SkillName = "Frans" });
            context.Skills.Add(new Models.Skill { SkillName = "Drupal" });
        }

        if (!context.Teachers.Any())
        {
            context.Teachers.Add(new Models.Teacher
            {
                FirstName = "Joris",
                LastName = "Hens",
                Campus = "Kruidtuin",
                Password = "testpass",
                Email = "Joris.Hens@"
            });
            context.Teachers.Add(new Models.Teacher
            {
                FirstName = "Anne",
                LastName = "Van Goetem",
                Campus = "Kruidtuin",
                Password = "testpass",
                Email = "Anne.Vangoetem@"
            });
            context.Teachers.Add(new Models.Teacher
            {
                FirstName = "Sofie",
                LastName = "Krekels",
                Campus = "De Ham",
                Password = "testpass",
                Email = "Sofie.Krekels@"
            });
            context.Teachers.Add(new Models.Teacher
            {
                FirstName = "Robby",
                LastName = "Vanelderen",
                Campus = "De Vest",
                Password = "testpass",
                Email = "Robby.Vanelderen@"
            });
        }

        if (!context.TeacherSkills.Any())
        {
            context.TeacherSkills.Add(new Models.TeacherSkill
            {
                Teacher_ID = 1,
                Skill_ID = 1,
            });
            context.TeacherSkills.Add(new Models.TeacherSkill
            {
                Teacher_ID = 1,
                Skill_ID = 4,
            });
            context.TeacherSkills.Add(new Models.TeacherSkill
            {
                Teacher_ID = 2,
                Skill_ID = 2,
            });
            context.TeacherSkills.Add(new Models.TeacherSkill
            {
                Teacher_ID = 3,
                Skill_ID = 3,
            });
            context.TeacherSkills.Add(new Models.TeacherSkill
            {
                Teacher_ID = 4,
                Skill_ID = 4,
            });
        }

    }

The teacher and skills seed without any problem, but I can't seed any skills to a teacher.

It doesn't give me any errors and I'm not sure what wrong.

I hope any of you can help, thanks!

Amalgamation

Answer 1

Add a call to

context.SaveChanges();  

between where you filled the teachers and where you are going to seed the teacherskills. This should commit the Skills and Teachers collections so your assumptions about the key columns (identity values) will be replaced by those actually generated when the INSERTs execute.

Furthermore the actual teachers' and skills' ID values can be retrieved and used in the TeacherSkills constructors to get rid of the "magic numbers" 1-4 in the Seed code.

Jennajenne

Thanks alot for you response, this was a simple fix! – Amalgamation

Answer 2

You look like you are assuming the IDs. If you have them as identity columns in your database that's probably not a great move.

With identity keys, you should call context.SaveChanges() to write to the db and get the ID's back. Then you should use the values from your objects rather than hardcoding ID values.

Backchat

Valid question - I concluded that from the fact that there's no explicit setting of IDs in his code. – Backchat

Answer 3

I am assuming you have navigation properties on Skill entity as follows

public class Skill{
 public string SkillName{get; set;}
 public virtual IList<Teacher> Teachers{get;set;}
}


protected override void Seed(Ability_Examen_ASP.Models.AbilityDbContext context){
 if (!context.Skills.Any())
    {


        if(!context.Skills.Any() && !context.Teachers.Any()){
            context.Skills.Add(new Models.Skill{ SkillName = "PHP", Teachers = new List<Teacher>{new Teacher{FirstName = "Joris",
            LastName = "Hens",
            Campus = "Kruidtuin",
            Password = "testpass",
            Email = "[email protected]"}} },

     );

 // repeat for other skills followed by list of teachers
          }

        context.SaveChanges();

      }
}

Tense