Identity map pattern

This article is about the Identity Map software design pattern. For the mathematical concept, see Identity function.

An identity map is a database access design pattern used to improve performance by providing a context-specific in-memory cache to prevent duplicate retrieval of the same object data from the database.

If the requested data has already been loaded from the database, the identity map returns the same instance of the already instantiated object, but if it has not been loaded yet, it loads it and stores the new object in the map. In this way, it follows a similar principle to lazy loading.

Four types of Identity Map

1. Explicit
2. Generic
3. Session
4. Class

See also

• Design pattern
• Active record
• Lazy loading