Question

I am trying to implement abstract base entity class which has overriden equals and GetHashcode…Here is my entity base class

public abstract class Entity<TId>
{

public virtual TId Id { get; protected set; }
protected virtual int Version { get; set; }

public override bool Equals(object obj)
{
  return Equals(obj as Entity<TId>);
}

private static bool IsTransient(Entity<TId> obj)
{
  return obj != null &&
         Equals(obj.Id, default(TId));
}

private Type GetUnproxiedType()
{
  return GetType();
}

public virtual bool Equals(Entity<TId> other)
{
  if (other == null)
    return false;

  if (ReferenceEquals(this, other))
    return true;

  if (!IsTransient(this) &&
      !IsTransient(other) &&
      Equals(Id, other.Id))
  {
    var otherType = other.GetUnproxiedType();
    var thisType = GetUnproxiedType();
    return thisType.IsAssignableFrom(otherType) ||
           otherType.IsAssignableFrom(thisType);
  }

  return false;
}

public override int GetHashCode()
{
  if (Equals(Id, default(TId)))
    return base.GetHashCode();
  return Id.GetHashCode();
}

}

How does the value of entity base Id gets assigned?

The primary keys of my classes have different datatypes and also names are different for each class.
Here is the sample of my classes:

public class Product : Entity
{
    public virtual Guid ProductId { get; set; }
    public virtual string Name { get; set; }
    public virtual string Description { get; set; }
    public virtual Decimal UnitPrice { get; set; }
}

public class Customer : Entity
{
    public virtual int CustomerID { get; set; }
    public virtual string FirstName { get; set; }
    public virtual string LastName { get; set; }
    public virtual int Age { get; set; }
}

I am bit confused on how to set ID property of the base class. Can anyone please suggest me on this, I will appreciate any help.

Answer 1

You just need to pass a type to the inherited base class.

See comments in the entities:

public class Product : Entity<Guid>
{
    // The ProductId property is no longer needed as the
    // Id property on the base class will be of type Guid
    // and can serve as the Id
    //public virtual Guid ProductId { get; set; }
    public virtual string Name { get; set; }
    public virtual string Description { get; set; }
    public virtual Decimal UnitPrice { get; set; }
}

public class Customer : Entity<int>
{
    // The CustomerID property is no longer needed as the
    // Id property on the base class will be of type int
    // and can serve as the Id
    // public virtual int CustomerID { get; set; }
    public virtual string FirstName { get; set; }
    public virtual string LastName { get; set; }
    public virtual int Age { get; set; }
}

Now in your NHibernate mapping files, just specify what the database column is for your Id properties.