列不是主键时与EF Code First的一对零或一对关系

Question

I'm developing an Entity Framework 6.1.3 Code First library, C# and .NET Framework 4.5.1.

I have a problem with a One-to-Zero-or-One relationship (or maybe is another kind of relationship).

I have two tables, Codes and HelperCodes , a code could have zero or one helper code. This is the sql script to create these two tables and their relationships:

CREATE TABLE [dbo].[Code]
(
    [Id] NVARCHAR(20) NOT NULL, 
    [Level] TINYINT NOT NULL, 
    [CommissioningFlag] TINYINT NOT NULL, 
    [SentToRanger] BIT NOT NULL DEFAULT 0, 
    [LastChange] NVARCHAR(50) NOT NULL, 
    [UserName] NVARCHAR(50) NOT NULL, 
    [Source] NVARCHAR(50) NOT NULL, 
    [Reason] NVARCHAR(200) NULL, 
    [HelperCodeId] NVARCHAR(20) NULL,
    CONSTRAINT [PK_Code] PRIMARY KEY CLUSTERED
    (
        [Id] ASC
    ),
    CONSTRAINT [FK_Code_LevelConfiguration]
       FOREIGN KEY ([Level])
        REFERENCES [dbo].[LevelConfiguration] ([Level]),
    CONSTRAINT [FK_Code_HelperCode]
       FOREIGN KEY ([HelperCodeId])
        REFERENCES [dbo].[HelperCode] ([HelperCodeId])
)

CREATE TABLE [dbo].[HelperCode]
(
    [HelperCodeId] NVARCHAR(20) NOT NULL, 
    [Level] TINYINT NOT NULL, 
    [CommissioningFlag] TINYINT NOT NULL, 
    [LastChange] NVARCHAR(50) NOT NULL,
    CONSTRAINT [PK_HelperCode] PRIMARY KEY CLUSTERED
    (
        [Id] ASC
    ),
    CONSTRAINT [FK_HelperCode_LevelConfiguration]
       FOREIGN KEY ([Level])
        REFERENCES [dbo].[LevelConfiguration] ([Level])
)

But, when I try to do the same with Entity Framework it doesn't do the same. My problem is in Codes and HelperCodes foreing key.

This is my Entity Framework Code First code:

public class Code
    {
        public string Id { get; set; }
        public byte Level { get; set; }

        // omitted for brevity

        public string HelperCodeId { get; set; }

        public virtual HelperCode HelperCode { get; set; }
    }

class CodeConfiguration : EntityTypeConfiguration<Code>
{
    public CodeConfiguration()
    {
        HasKey(c => c.Id);

        Property(c => c.Id)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

        Property(c => c.Id)
            .HasMaxLength(20);

        // omitted for brevity

        Property(c => c.HelperCodeId)
            .HasMaxLength(20)
            .IsOptional();

        HasOptional(c => c.HelperCode)
            .WithRequired(hc => hc.Code);
    }
}

public class HelperCode
{
    public string HelperCodeId { get; set; }
    public byte Level { get; set; }
    public byte CommissioningFlag { get; set; }
    public string LastChange { get; set; }

    public virtual Code Code { get; set; }
}

class HelperCodeConfiguration : EntityTypeConfiguration<HelperCode>
{
    public HelperCodeConfiguration()
    {
        HasKey(h => h.HelperCodeId);

        Property(h => h.HelperCodeId)
            .HasMaxLength(20);

        Property(h => h.Level)
            .IsRequired();

        Property(h => h.CommissioningFlag)
            .IsRequired();

        Property(h => h.LastChange)
            .IsOptional()
            .HasMaxLength(50);
    }
}

This Entity Code First code generates a foreign key in HelperCodes table using HelperCodes.HelperCodeId referencing Codes.Id .

Entity Framework only allows this kind of relationship if both tables have the same primary key.

Any idea about how to resolve this EF bug?

Answer 1

First: Remove the HelperCodeId from the Code class:

public class Code
{
    public string Id { get; set; }
    public byte Level { get; set; }

    // omitted for brevity

    public virtual HelperCode HelperCode { get; set; }
}

In the Code configuration:

.HasOptional(i => i.HelperCode)
.WithRequired(i => i.Code);

Generated migration:

CreateTable(
    "dbo.Codes",
    c => new
        {
            Id = c.String(nullable: false, maxLength: 128),
            Level = c.Byte(nullable: false),
        })
    .PrimaryKey(t => t.Id);

CreateTable(
    "dbo.HelperCodes",
    c => new
        {
            HelperCodeId = c.String(nullable: false, maxLength: 128),
            Level = c.Byte(nullable: false),
            CommissioningFlag = c.Byte(nullable: false),
            LastChange = c.String(),
        })
    .PrimaryKey(t => t.HelperCodeId)
    .ForeignKey("dbo.Codes", t => t.HelperCodeId)
    .Index(t => t.HelperCodeId);

Only the HelperCodes table should have the foreign key statement.

HelperCodeId is a primary key and also a foreign key, so it ensures the 0:1 relationship.

Answer 2

The relationship is wrong;Change your code to blow code

 public class HelperCode
{

    public byte Level { get; set; }
    public byte CommissioningFlag { get; set; }
    public string LastChange { get; set; }
    public string CodeId { get; set; }
    public virtual Code Code { get; set; }
}

  public class Code
{
    public string Id { get; set; }
    public byte Level { get; set; }
    public virtual HelperCode HelperCode { get; set; }
}

I also configure the relationship from the other side.

public  class CodeConfiguration : EntityTypeConfiguration<Code>
{
    public CodeConfiguration()
    {
        HasKey(h => h.Id);

        HasOptional(x => x.HelperCode).WithRequired(x => x.Code);
    }
}