具有多个不同类型的多个父项之一的实体

Question

I'm currently working on a C# EF MVC project in combination with a MySql database and I am trying to setup my database schema through a code-first approach (with migrations enabled). For my example I have simplified my model down to the 3 classes shown below:

public class Message
{
  [Key]
  public int MessageId { get; set; }
  // Some properties ...

  // There will always be one filled in and not the other
  public virtual CorrectedContent CorrectedContent { get; set; }
  public virtual MessageContent MessageContent { get; set; }
}

public class CorrectedContent
{
  [Key]
  public int CorrectedContentId { get; set; }

  public virtual Message Message { get; set; }
  // ...
  public MessageContent MessageContent { get; set; }  // Nullable
}

public class MessageContent
{
  [Key]
  public int MessageContentId { get; set; }

  public virtual Message Message { get; set; }
  public virtual CorrectedContent CorrectedContent
  // ...
}

To make sure the relations were mapped properly I also used the EF Fluent Api on my DbContext.

public class TestContext: DbContext
{
  public TestContext(): base("TestContext") { }
  // My DbSets and such ...

  protected override void OnModelCreating(DbModelBuilder modelBuilder)
  {
    modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();

    modelBuilder.Entity<CorrectedContent>()
      .HasOptional(x => x.MessageContent)
      .WithRequired(y => y.CorrectedContent)
      .WillCascadeOnDelete();

    modelBuilder.Entity<Message>()
      .HasOptional(x => x.MessageContent)
      .WithRequired(y => y.Message)
      .WillCascadeOnDelete();

    modelBuilder.Entity<Message>()
      .HasOptional(x => x.CorrectedContent)
      .WithRequired(y => y.Message)
      .WillCascadeOnDelete();
  }
}

The issue I have is when I try to add a Message with MessageContent to my database I get:

Cannot add or update child row: a foreign key constraint fails ("DbName"."MessageContent", CONSTRAINS "FK_MessageContent_CorrectedContent_MessageContentId " FOREIGN KEY ("MessageContentId ") REFERENCES "CorrectedContent" ("CorrectedContentId") ON DELETE CASCADE ON UPDATE CASCADE)

I have tried putting both entities on "withOptional" but that didn't work, I also tried working with a mutual interface for both the Message and CorrectedContent .

So the Message should have a one-to-one-or-zero relationship to MessageContent , CorrectedContent also has a one-to-one-or-zero relationship with MessageContent and Message has a one-to-one-or-zero with CorrectedContent .

Answer 1

My current solution:

Because the XSD (and send in xml files) where my data would come from was too complicated to transform into a proper database model I opted for a less than ideal solution where I only have 2 classes like shown below.

public class Message
{
  [Key]
  public int MessageId { get; set; }
  // Some properties ...

  public virtual MessageContent MessageContent { get; set; }
}

public class MessageContent
{
  [Key]
  public int MessageContentId { get; set; }

  public virtual Message Message { get; set; }

  [Required, Column(TypeName = "text")]
  public string XMLString { get; set; }

  [Required]
  public MessageType Type { get; set; }
}

public enum MessageType
{
  Correction,
  Normal,
  // more options ...
}

In the model I only open the first element of a received XML which is always of type Message . Then I look for the child element and get its type which is MessageType . The XMLString property contains this child in string representation.

I know this is a bad designed solution but it works for my application just fine. I use the XSD (classes) that was provided to my on my front-end so I only have to parse the XMLString to the XSD classes.

Any better solutions are always welcome.