Abstract

DbContext instances track changes made to their entities. The tracked entities report the changes to the database when SaveChanges is called.

Entity instances become tracked when they are: (1) returned from a query; (2) explicitly attached to a DbContext via Add, Attach, or Update; (3) detected as new entities connected to existing tracked entities.

Entity instances are no longer tracked when: (1) the DbContext is disposed; (2) the change tracker is cleared; (3) the entities are explicitly detached.

Change tracking occurs at the property level. If only a single property value is modified, then the database update will change only that value.

Entity States

Every entity is associated with an EntityState. The states:

• Detached — entity is not being tracked by DbContext
• Added — entity are new and not yet in the database
• Unchanged — entity not changed since queried from database
• Modified — entity changed since queried from database
• Deleted — entity exists in database but marked to be deleted when SaveChanges is called

Entity states rarely need to be manipulated manually. Unless explicitly necessary, use the same DbContext instance for both querying entities and updating them via SaveChanges.

Sequencing

EF Core will process database CRUD operations in this order:

1. INSERT
2. UPDATE
3. DELETE