一对一或零关系，其中FK是依赖表上的复合PK的一部分

Question

I'm developing a library with Entity Framework 6.1.2 for these two tables:

CREATE TABLE [dbo].[CODES]
(
    [CODE] [nvarchar](20) NOT NULL,
    [ ... ],
    CONSTRAINT [PK_CODES] PRIMARY KEY CLUSTERED 
    (
        [CODE] ASC
    )
)

CREATE TABLE [dbo].[AGGREGATIONS]
(
    [ID_AGGREGATION] INT IDENTITY(1,1) NOT NULL, 
    [CODE_LEVEL] TINYINT NOT NULL, 
    [CODE] NVARCHAR(20) NOT NULL,
    [ ... ], 
    CONSTRAINT [PK_AGGREGATIONS] PRIMARY KEY CLUSTERED
    (
        [ID_AGGREGATION] ASC
    ),
    CONSTRAINT [FK_AGGREGATIONS_CODES] FOREIGN KEY ([CODE]) REFERENCES [dbo].[CODES] ([CODE])
)

Relationship:

I CODES could have zero or one AGGREGATIONS , but an AGGREGATIONS will have one CODES .

To do it, I have these two entity classes:

public class CODES
{
    public string CODE { get; set; }
    [ ... ]

    public virtual AGGREGATIONS Aggregation { get; set; }
    public virtual AGGREGATION_CHILDS AggregationChild { get; set; }
}
public class AGGREGATIONS
{
    public int ID_AGGREGATION { get; set; }
    public string CODE { get; set; }
    public byte CODE_LEVEL { get; set; }

    public virtual CODES Code { get; set; }
}

I have tried this to set relationship between AGGREGATIONS and CODES on Aggregations' EntityTypeConfiguration<AGGREGATIONS> :

HasKey(ag => ag.ID_AGGREGATION);
HasRequired(ag => ag.Code).WithOptional(c => c.Aggregation);

But I don't know how to set AGGREGATIONS.CODE as foreign key in this relantionship.

How can I set FK on this relationship?

UPDATE

I need to use AGGREGATIONS.ID_AGGREGATION because there is another table that has a foreign key to AGGREGATIONS and to CODES tables:

CREATE TABLE [dbo].[AGGREGATION_CHILDS]
(
    [ID_AGGREGATION] [int] NOT NULL,
    [CODE] [nvarchar](20) NOT NULL,
    [CODE_LEVEL] [tinyint] NOT NULL,
    [POSITION] [int] NOT NULL,
    CONSTRAINT [PK_AGGREGATION_CHILDS] PRIMARY KEY CLUSTERED 
    (
        [ID_AGGREGATION] ASC,
        [CODE] ASC
    ), 
    CONSTRAINT [FK_AGGREGATION_CHILDS_AGGREGATIONS] FOREIGN KEY ([ID_AGGREGATION]) REFERENCES [AGGREGATIONS]([ID_AGGREGATION]), 
    CONSTRAINT [FK_AGGREGATION_CHILDS_CODES] FOREIGN KEY ([CODE]) REFERENCES [CODES]([CODE])

If I do what you have recommend me in the answer , I will have two columns CODE in AGGREGATION_CHILDS table. One of them will be foreign key to AGGREGATIONS table and also to CODES table. And the other one FK to CODES table.

Answer 1

In one-to-one relationships EF requires the Key of the dependent entity also has to be the Foreign Key to the principal, so, your model would be like this:

public class CODES
{
  [Key]
  public string CODE { get; set; }
  [ ... ]

  public virtual AGGREGATIONS Aggregation { get; set; }
}

public class AGGREGATIONS
{
   [Key, ForeignKey("Codes")]
   public string CODE { get; set; }
   public byte CODE_LEVEL { get; set; }

   public virtual CODES Code { get; set; }
}

If you need to use Fluent Api, I think you could do this in the configuration class of Aggregations :

HasKey(ag=>ag.Code);
HasRequired(ag => ag.Code).WithOptional(c => c.Aggregation);

You can find more info in this page .

Update 1

To achieve what you want, you can't declare a FK property in the dependent entity due to the restriction that I comment above. So your model would be like this:

public class CODES
{
  [Key]
  public string CODE { get; set; }

  [Required]
  public virtual AGGREGATIONS Aggregation { get; set; }

  public ICollection<AGGREGATION_CHILDS> AggregationChilds { get; set; }
}
public class AGGREGATIONS
{
   [Key]
   public int ID_AGGREGATION { get; set; }

   public byte CODE_LEVEL { get; set; }

   public virtual CODES Code { get; set; }

   public ICollection<AGGREGATION_CHILDS> AggregationChilds { get; set; }

}

public class AGGREGATION_CHILDS
{
   [Key,Column(Order = 0),ForeignKey("Code")]
   public string CODE { get; set; }

   [Key,Column(Order = 1),ForeignKey("Aggregation")]
   public int ID_AGGREGATION { get; set; }

   public virtual CODES Code { get; set; }

   public virtual AGGREGATIONS Aggregation { get; set; }
}

If you don't want to use Data Annotations you can delete all the attributes and specify the same using Fluent Api in your configuration classes:

 public class CodesMap : EntityTypeConfiguration<CODES>
 {
    public CodesMap()
    {
        // Primary Key
        this.HasKey(t => t.CODE);
    }
 }

 public class AggregationsMap : EntityTypeConfiguration<AGGREGATIONS>
 {
    public AggregationsMap()
    {
        // Primary Key
        this.HasKey(t => t.ID_AGGREGATION);
        HasRequired(ag => ag.Code).WithOptional(c => c.Aggregation);
    }
 }

 public class AggregationChildsMap : EntityTypeConfiguration<AGGREGATIONS_CHILDS>
 {
    public AggregationChildsMap()
    {
        // Primary Key
        this.HasKey(t => new{t.CODE,t.ID_AGGREGATION});
        HasRequired(t => t.Code).WitMany(c => c.AggregationChilds).HasForeignKey(t=>t.CODE);
        HasRequired(t => t.Aggregation).WitMany(ag => ag.AggregationChilds).HasForeignKey(t=>t.ID_AGGREGATION);

    }
 }

Update 2

It's not possible specify a composite PK in the AGGREGATION_CHILDS and configure a one-to-one relationship between this entity and AGGREGATIONS , unless that composite keys are the keys in AGGREGATIONS too. If you want to create an one-to-one relationship and specify a FK property in the dependend entity, then that FK must be PK too, so both entity must share the same PK(s). If you declare another Key in that dependend entity, where is the FK related to another relationship, EF would expect both relationships should be one-to-many (as the example that I show in the Update 1). If you try to create two one-to-one relationships and you try to compound the PK of the dependent end with the PKs of the principals, then you will receive this exception:

AGGREGATION_CHILDS_Aggregation_Source: : Multiplicity is not valid in Role 'AGGREGATION_CHILDS_Aggregation_Source' in relationship 'AGGREGATION_CHILDS_Aggregation'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.

AGGREGATION_CHILDS_Code_Source: : Multiplicity is not valid in Role 'AGGREGATION_CHILDS_Code_Source' in relationship 'AGGREGATION_CHILDS_Code'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.

Answer 2

I think you're nearly there. For an Optional Codes.Aggregation try:

HasRequired(ag => ag.Code).WithOptional(c => c.Aggregation); 

or in your context class:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Aggregations>()
                .HasRequired(a => a.Code)
                .WithOptional(c => c.Aggregation);
}

Answer 3

This is how I have solved the problem:

public class CODES
{
    public string CODE { get; set; }
    public byte CODE_LEVEL { get; set; }
    [ ... ]

    public virtual AGGREGATION_CHILDS AggregationChild { get; set; }
    public virtual AGGREGATIONS Aggregation { get; set; }
}
public class AGGREGATIONS
{
    public string CODE { get; set; }
    public string CREATED { get; set; }

    public virtual ICollection<AGGREGATION_CHILDS> AggregationChilds { get; set; }
    public virtual CODES Code { get; set; }
}
public class AGGREGATION_CHILDS
{
    public string CODE { get; set; }
    public string PARENT_CODE { get; set; }
    public int POSITION { get; set; }

    public AGGREGATIONS Aggregation { get; set; }
    public CODES Code { get; set; }
}

And their maps:

class AGGREGATIONSConfiguration : EntityTypeConfiguration<AGGREGATIONS>
{
    public AGGREGATIONSConfiguration()
    {
        HasKey(ag => ag.CODE);

        Property(ag => ag.CODE)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

        Property(ag => ag.CODE)
            .HasMaxLength(20)
            .IsRequired();

        Property(ag => ag.CREATED)
            .HasMaxLength(50)
            .IsOptional();

        HasRequired(ag => ag.Code)
            .WithOptional(c => c.Aggregation)
            .WillCascadeOnDelete(false);
    }
}
class AGGREGATION_CHILDSConfiguration : EntityTypeConfiguration<AGGREGATION_CHILDS>
{
    public AGGREGATION_CHILDSConfiguration()
    {
        HasKey(ag_ch => ag_ch.CODE);

        Property(ag_ch => ag_ch.CODE)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

        Property(ag_ch => ag_ch.CODE)
            .HasMaxLength(20)
            .IsRequired();

        Property(ag_ch => ag_ch.PARENT_CODE)
            .HasMaxLength(20)
            .IsRequired();

        HasRequired(ag_ch => ag_ch.Aggregation)
            .WithMany(ag => ag.AggregationChilds)
            .HasForeignKey(ag_ch => ag_ch.PARENT_CODE);

        HasRequired(ag_ch => ag_ch.Code)
            .WithOptional(c => c.AggregationChild)
            .WillCascadeOnDelete(false);
    }
}

CODESConfiguration is not relevant here.

I have used CODE as PK on AGGREGATIONS and on AGGREGATION_CHILDS and also as FK to CODES table. I have remove ID_AGGREGATION from AGGREGATIONS table and remove composite PK on AGGREGATION_CHILDS table.

I hope it helps someone that have the same problem with One-to-Zero-or-One relationship.