如何在父实体中拥有一个属性，该父实体的值属于子实体，而EF6和Code-First则将其下两层

Question

I need to mantain udpated a property in a parent entity that belongs to a child entity two levels down. I am using EF6 with Code First and DataAnnotations in a Asp.Net/MVC application.

Having these entitites:

public class Parent 
{
    [Key]
    public int IdParent {get; set;}

    // ...other properties

    //The value of this property belongs to the Child table, two levels down.    
    public int Status { get; set; }     
    public Intermediate Intermediate { get; set; }
}   


public class Intermediate
{
    [Key, ForeignKey("Parent")]
    public int IdIntermediate { get; set;}

    // ... other properties

    public Parent Parent { get; set; }
    public Child Child { get; set; }
}

public class Child 
{
   [Key, ForeignKey("Intermediate")]
   public int IdChild { get; set; }

   //...other properties

   public int Status { get; set; } // This is the property I need to keep updated in Parent Class

   public Intermediate Intermediate { get; set; } 
}

The property Status in Parent gives to the user a quick view of the result of the process executed on Child which has detailed information about the execution.

I am evaluating these solution, I would appreciate your recommendations about which of them is more appropiate or another better solution.

• Option 1: Create a trigger in database to keep updated the field in Parent table. This option will produce a cleaner code in my entities but requires to create an isolated migration for the trigger because it has to be a SQL command, and it is hard to maintain.

   public partial class AddUpdateTriggerOnChildMigration : DbMigration { public override void Up() { Sql("CREATE OR REPLACE TRIGGER [Child_UpdateStatus] FOR UPDATE ON dbo.Child..."); } public override void Down() { Sql("DROP TRIGGER [Child_UpdateStatus]"); } } 

• Option 2: To keep the field only in Child table and make the Status property computed on Parent entity. But I do not know how to get this to work with DataAnnotations or with Fluent API.

   [DatabaseGenerated(DatabaseGeneratedOption.Computed)] public int Status { get; private set; } 

• Option 3: To make NotMapped the property Parent.Status and fill it by code from the Child entity. This seems the worst solution and it is also hard to maintain and it will not work when the entity is not attached to the context.

   public class Parent { public int IdParent { get; set; } // ... [NotMapped] public int? Status { get { return this.Intermediate == null ? null : this.parent.Intermediate.Child.Status; } } public Intermediate Intermediate { get; set; } } 

Answer 1

I give you a 4th option: override SaveChanges as follows:

public partial class MyDbContext : DbContext
{
    public override int SaveChanges()
    {
        try
        {
            var changeSet = ChangeTracker.Entries<Child>();

            if (changeSet != null)
            {
                foreach (var entry in changeSet.Where(c => c.State == EntityState.Added || c.State == EntityState.Modified))
                {
                    // Update here the parent
                }
            }

            return base.SaveChanges();
        }
        catch (Exception exception)
        {

        }
    }
}

The idea here is that when you save the changes of your context, you loop over all the entities of type Child that have been added or modified and then you can properly update the Status property of your Parent class