EF - Code First：在多对多关系中保存值的问题

Question

I'm trying to add a tagging system to a webapplication build on MVC3 with EF Code First for data access. The base is pretty simple. I have Projects, Companies and People who can have 1 or more tags. I do not want to save the tags for each entity alone, so the tag class has 3 ICollections: People, Companies and Projects. Each of the entities has an ICollection of tag. see the code below

public class Project 
{
    public int ID { get; set; }
    public virtual ICollection<Tag> Tags { get; set; }
}

public class Person
{
    public int ID { get; set; }
    public virtual ICollection<Tag> Tags { get; set; }
}

public class Company
{
    public int ID { get; set; }
    public virtual ICollection<Tag> Tags { get; set; }
}

public class Tag
{
    [Key]
    public int TagID { get; set; }
    public String Name { get; set; }

    public virtual ICollection<Project> Projects { get; set; }
    public virtual ICollection<Person> People { get; set; }
    public virtual ICollection<Company> Companies { get; set; }
}

In the context the mapping is set like this:

modelBuilder.Entity<Tag>()
    .HasMany(t => t.Projects)
    .WithMany(p => p.Tags)
    .Map(m =>
    {
        m.MapLeftKey("ID");
        m.MapRightKey("TagID");
        m.ToTable("TagProjects");
    });


modelBuilder.Entity<Tag>()
    .HasMany(t => t.People)
    .WithMany(p => p.Tags)
    .Map(m => 
    {
        m.MapLeftKey("ID");
        m.MapRightKey("TagID");
        m.ToTable("TagPeople");
    });

modelBuilder.Entity<Tag>()
    .HasMany(t => t.Companies)
    .WithMany(p => p.Tags)
    .Map(m =>
    {
        m.MapLeftKey("ID");
        m.MapRightKey("TagID");
        m.ToTable("TagCompanies");
    });

Now when I try to add a tag to a project like this:

public void AddTagToProject(int tagId, int projectId)
{
    ProjectRepository projectRepository = new ProjectRepository();
    Project project = projectRepository.GetProjectByID(projectId);
    project.Tags.Add(GetTagByID(tagId));

    Save();
}

there is no exception, but the project has no tags added to it either. Anyone have an idea where to look?

public Tag GetTagByID(int tagId) 
{ 
    return db.Tags
        .Where(t => t.TagID == tagId)
        .First(); 
}

I've found the solution, the problem was that the project was not correctly updated and the values were never saved.

Answer 1

Have you made sure your database doesn't have any oddly named columns generated by EF 4.1? I had that happen once, and the FK column was called UserTrialLicense_UserTrialLicenseID. So anytime I tried to eager-load anything using.Include, it would not work.