Question

I am still on my quest to port from a Model First to Code First implementation of EntityFramework. I have made significant progress, with the help of Eranga. I have run into another snag, and I just cant explain what is hapening. I have two Entity objects Topic and Course

• A Topic can have one Course that is required
• A Course can have 0 or more topics

when i execute the following linq it generates wierd SQL

    var topics = from o in db.Topics where o.ParentTopic == null && 
            o.Course.Id == c.Id select o;

The SQL generated is

SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[Name] AS [Name], 
[Extent1].[ShortDescription] AS [ShortDescription], 
[Extent1].[LongDescription] AS [LongDescription], 
[Extent1].[Property] AS [Property], 
[Extent1].[Difficulty] AS [Difficulty], 
[Extent1].[Weight] AS [Weight], 
[Extent1].[Course_Id] AS [Course_Id], 
[Extent1].[ParentTopic_Id] AS [ParentTopic_Id], 
[Extent1].[Course_Id1] AS [Course_Id1]
FROM [dbo].[Topics] AS [Extent1]
WHERE ([Extent1].[ParentTopic_Id] IS NULL) AND ([Extent1].[Course_Id] = @p__linq__0)

Notice that there is an added field called Course_Id1 that is not in my object and not declared as a foreign key. I thought that in OnModelCreating() I had specified the parent child relationship correctly from both sides (I would have thought you only needed to do it from either side), but i cant get EntityFramework not to generate the extra field that obviously does not exist in the database. Remember my database was originally created using a ModelFirst approach.

Can anyone explain where the extra field is comming from????

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        //Topic
        modelBuilder.Entity<Topic>()
            .HasRequired(m => m.Course)
            .WithMany(m=>m.Topics)
            .HasForeignKey(m => m.Course_Id);
        modelBuilder.Entity<Topic>()
            .HasOptional(m => m.ParentTopic)
            .WithMany(m => m.ChildTopics)
            .HasForeignKey(m => m.ParentTopic_Id);

        //////// lots of code removed for brevity. //////

        modelBuilder.Entity<Course>()
            .HasMany(m=>m.Topics)
            .WithRequired(m => m.Course)
            .HasForeignKey(m => m.Course_Id);
    }


public partial class Topic
{
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    public string ShortDescription { get; set; }
    public string LongDescription { get; set; }
    public string Property { get; set; }
    public double? Difficulty { get; set; }
    public double? Weight { get; set; }

    [JsonIgnore]
    public virtual Course Course { get; set; }
    public int Course_Id { get; set; }

    [JsonIgnore]
    public virtual ICollection<Question> Questions { get; set; }

    [JsonIgnore]
    public virtual ICollection<Topic> ChildTopics { get; set; }

    [JsonIgnore]
    public virtual Topic ParentTopic { get; set; }
    public int? ParentTopic_Id { get; set; }

    [JsonIgnore]
    public virtual ICollection<RTIQueueEntryData> RTIQueueEntryData { get; set; }

    [JsonIgnore]
    public virtual ICollection<Intervention> Interventions { get; set; }

    [JsonIgnore]
    public virtual ICollection<RtiStudentGroup> RtiStudentGroups { get; set; }
}

public partial class Course
{
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    [Required]
    public string Description { get; set; }
    public string Version { get; set; }
    public string Year { get; set; }
    public string ImportedId { get; set; }
    [Required]
    public string LocalCourseNumber { get; set; }
    [Required]
    public string NCESCourseNumber { get; set; }
    [Required]
    public string StateCourseNumber { get; set; }
    public int? Grade { get; set; }

    [JsonIgnore]
    public virtual ICollection<Topic> PerformanceIndicators { get; set; }

    [JsonIgnore]
    public virtual Department Department { get; set; }
    public int DepartmentId { get; set; }

    [JsonIgnore]
    public virtual ICollection<StudentGroup> StudentGroups { get; set; }

    [JsonIgnore]
    public virtual ICollection<CutPointTemplate> CutPointTemplates { get; set; }

    [JsonIgnore]
    public virtual School School { get; set; }
    public int School_Id { get; set; }

    [JsonIgnore]
    public virtual ICollection<Staff> RTIStaff { get; set; }

    [JsonIgnore]
    public virtual ICollection<Topic> Topics { get; set; }
}

Answer 1

You have another relationship between Course and Topic created by convention due to this navigation property:

public virtual ICollection<Topic> PerformanceIndicators { get; set; }

EF will put an (invisible, not exposed) end of the relationship into the Topic class. By default the relationship is one-to-many. Hence you get an additional foreign key property in the Topics table (= Course_Id1).