a.Identity Field

  1. Motivation
    1. Saves a database ID field in an object to maintain identity between an in-memory object and a database row.
  2. Summary
    1. Business object only store ID filed of data row and use the ID key to operates on data row in data table directly.
    2. Challenging part is to select correct key property and primary key is most preferred choice. 
    3. I would mark this pattern obsolete for custom implementation because   frameworks like EF provides similar logic  but still can be used for very simple Domain Model.
  3. When to Use
    1. Business object are simple and making frequent database calls are acceptable.

  4. Related Patterns
    1. This pattern generally used with Domain Model or Row Data Gateway.
    2. Identity Map is an alternative pattern that can be used in replacement this pattern.