Code first, navigation property on subclassed entity : The Official Microsoft ASP.NET Forums

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bagosm

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22 Posts

Code first, navigation property on subclassed entity

Jun 29, 2012 08:20 PM|LINK

Entities:

public class ParentEntity
    {
        [Key]
        public string ParentEntityID { get; set; }

        // Navigation Properties
        public virtual ICollection<ChildEntity>  ChildEntities { get; set; }
        public virtual ICollection<ChildEntitySubclass> ChildEntitySubclasses{ get; set; }
    }

    public class ChildEntity
    {
        [Key, Column(Order = 0)]
        public string ParentEntityID { get; set; }

        [Key, Column(Order = 1)]
        public string CompositeKeyExtraPart { get; set; }



        // Navigation Properties
        [InverseProperty("ChildEntities")]
        [ForeignKey("ParentEntityID ")]
        public virtual ParentEntity ParentEntity { get; set; }
    }


    [Table("ChildEntitySubclass")]
    public class ChildEntitySubclass : ChildEntity
    {
        public int DummyExtraProp { get; set; }
    }

Updating because this problem is different than I though. As it seems, it is impossible to get the second navigation property (ChildEntitySubclasses) on ParentEntity to work. Can anyone confirm this?

Edited by bagosm on Jun 29, 2012 08:53 PM

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Decker Dong ...

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Re: Code first, navigation property on subclassed entity

Jul 01, 2012 01:10 AM|LINK

bagosm

Updating because this problem is different than I though. As it seems, it is impossible to get the second navigation property (ChildEntitySubclasses) on ParentEntity to work. Can anyone confirm this?

Hello:D

No，I can get the second navigation property。Please check this sample（you are not right and I cannot confirm）……

namespace CSharp
{
    #region EntityClasses
    public class ParentEntity
    {
        [Key]
        public string ParentEntityID { get; set; }
 
        // Navigation Properties 
        public virtual ICollection<ChildEntity> ChildEntities { get; set; }
        public virtual ICollection<ChildEntitySubclass> ChildEntitySubclasses { get; set; }
    }
 
    public class ChildEntity
    {
        [Key, Column(Order = 0)]
        public string ParentEntityID { get; set; }
 
        [Key, Column(Order = 1)]
        public string CompositeKeyExtraPart { get; set; }
 
 
 
        public virtual ParentEntity ParentEntity { get; set; }
    }
 
    [Table("ChildEntitySubclass")]
    public class ChildEntitySubclass : ChildEntity
    {
        public int DummyExtraProp { get; set; }
    }
    #endregion
 
    #region DbGenerator
    public class DbGenerator : DbContext
    {
        public DbSet<ParentEntity> ParentEntities { get; set; }
        public DbSet<ChildEntity> ChildEntities { get; set; }
        public DbSet<ChildEntitySubclass> ChildEntitySubclasses { get; set; }
    }
    #endregion
    /// <summary>
    /// Test class
    /// </summary>
    public class MainTest
    {
        static void Main(string[] args)
        {
            using (DbGenerator dbg = new DbGenerator())
            {
                //Initailizing the db to zero
                Database.SetInitializer<DbGenerator>(new DropCreateDatabaseAlways<DbGenerator>());
 
                //Try adding things
                dbg.ParentEntities.Add(new ParentEntity { ParentEntityID = "1", ChildEntities = new List<ChildEntity> { new ChildEntity { ParentEntityID = "1", CompositeKeyExtraPart = "Test" } }, ChildEntitySubclasses = new List<ChildEntitySubclass> { new ChildEntitySubclass { ParentEntityID = "1", CompositeKeyExtraPart = "Test2", DummyExtraProp = 1 } } });
                dbg.SaveChanges();
 
                //Fetch ChildEntitySubclasses
                ParentEntity pe = dbg.ParentEntities.Find("1"); //Find out the exact key record
                //List all
                foreach (var item in pe.ChildEntitySubclasses)
                {
                    Console.WriteLine(item.CompositeKeyExtraPart+"<===>"+item.DummyExtraProp);
                }
            }
        }
    }
}

Edited by decker dong - msft on Jul 01, 2012 01:11 AM
Marked as answer by decker dong - msft on Jul 05, 2012 02:16 AM

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bagosm

Member

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22 Posts

Re: Code first, navigation property on subclassed entity

Jul 01, 2012 10:31 AM|LINK

Hello decker!

Thanks for the reply and the attention to this, however I think the reason this works, is only because you initialize the parent item with the list of subclasses inside it. IE, if you go over to the database, you will find that the subclass table has an additional foreign key directly pointing to ParentEntity, which is redundant, but the way you insert the item this field is filled automatically.

So for the test to fail, you have to insert the ParentEntity first, then on dbg.ChildEntitySubclasses insert the respective items and on dbg.ChildEntity. You will see that they wont be related because the ParentEntity_ParentEntityID property (database side) on them will be null.

Edited by bagosm on Jul 01, 2012 10:32 AM

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Decker Dong ...

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Re: Code first, navigation property on subclassed entity

Jul 02, 2012 01:25 AM|LINK

bagosm
So for the test to fail, you have to insert the ParentEntity first, then on dbg.ChildEntitySubclasses insert the respective items and on dbg.ChildEntity. You will see that they wont be related because the ParentEntity_ParentEntityID property (database side) on them will be null.

Hello：）

As far as I see，One-To-Many relationship you should do to create a "One" instance part，and then do to create the instance of "Many" part and assign to the "Many" entitySet for the "One"。

bagosm
you will find that the subclass table has an additional foreign key directly pointing to ParentEntity, which is redundant,

Yes I suggest you removing it，it's really redundant……

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bagosm

Member

5 Points

22 Posts

Re: Code first, navigation property on subclassed entity

Jul 02, 2012 09:49 AM|LINK

Hello!

Thanks for the follow-up. I dont think you understood what I said before, let me say it more clearly.

In the example you made, on the SQL Server side, you will get this:

table: ChildEntitySubclass


         
      DummyExtraProp
K FK1 ParentEntityID
K FK1 CompositeKeyExtraPart
   FK2 ParentEntity_ParentEntityID  // This shouldn't exist! Duplicate FK to the parent Entity

So if you do on your test:

dbg.ParentEntities.Add(new ParentEntity { ParentEntityID = "1"});

dbg.ChildEntities.Add(new ChildEntity { ParentEntityID = "1", CompositeKeyExtraPart = "Test" } });
dbg.ChildEntitySubclasses.Add(new ChildEntitySubclass { ParentEntityID = "1", CompositeKeyExtraPart = "Test2", DummyExtraProp = 1 });

dbg.SaveChanges();

Test will fail because FK2 is empty => (pe.ChildEntitySubclasses == null) BUT (pe.ChildEntities.Count == 2).

So what I have learnt is I have to do is:

public class ParentEntity
    {
        [Key]
        public string ParentEntityID { get; set; }
 
        // Navigation Properties 
        public virtual ICollection<ChildEntity> ChildEntities { get; set; }

        public IEnumerable<ChildEntitySubclass> ChildEntitySubclasses {
            get { return ChildEntities.OfType<ChildEntitySubclass>(); }
        }
    }

This works! But ChildEntities = ChildEntities + ChildEntitySubclasses. Is there a way to get only ChildEntity base classes? What I have done is:

public IEnumerable<ChildEntity> ChildEntityOnlyBaseClasses {
           get { return AllComponentPages.Where(r => !(r is ChildEntitySubclass)); } }
        }

But using "! is ChildEntitySubclass" is not right, I need something like "Where R is ONLY-THE-BASE of ChildEntity".

Summing up: Problem now is mainly this, how can I get a List<ChildEntity> with NO ChildEntitySubclass?