DDD, value objects and ORM

Question

Value objects do not have identity. ORM needs identity to update the database.

How to trick ORM?

(Marking Id for value object as internal won\'t work bec

Answer 1

You have 2 options:

• Save the Value Object in the same Aggregate Root table
• Separate table using the Aggregate Root as the ID

For your example, something like:

public class Customer : Entity
{
    public Guid CustomerID { get; }
    public string LastName { get; set; }
    public Address HomeAddress { get; set; }
}

public class Address : ValueObject
{
    public string Street { get; set; }
    public string City { get; set; }
    public string ZipCode { get; set; }
}

Option 1 (Pseudo-SQL):

​CREATE​ ​TABLE​ Customer (
      // aggregate root
​     customerId ​int​ ​NOT​ ​NULL​,
      lastName VARCHAR(30),

      // value object
      street VARCHAR(100),
      city VARCHAR(50),
      zip VARCHAR(10)
​     ​CONSTRAINT​ PK_Customer ​PRIMARY​ ​KEY​ (customerId)
​   )

Option 2 (Pseudo-SQL):

// aggregate root
CREATE​ ​TABLE​ Customer (
​   customerId ​int​ ​NOT​ ​NULL​,
    lastName VARCHAR(30)
    CONSTRAINT​ PK_Customer ​PRIMARY​ ​KEY​ (customerId)
    )

// value object
CREATE​ ​TABLE​ Address (     
​     customerId ​int​ ​NOT​ ​NULL​, // same ID from Customer

​     street VARCHAR(100),
      city VARCHAR(50),
      zip VARCHAR(10)
      ​CONSTRAINT​ PK_Address ​PRIMARY​ ​KEY​ (customerId)
    )

• Then you can create a toDomain(sqlResult) function to convert the query result in your domain object
• Try to use one-table approach by default