1. .NET Database Technologies:
Entity Framework
additional notes – part 1

2. “Making the conceptual level real” (Blakeley, 2006)
Raises the level of abstraction from the logical (relational) level to the conceptual (entity) level
Provides a data model that can define the structure essence of entities
Entities and relationships as first-class objects
Provides a concrete representation that allows us to manipulate data at this level
Entity Data Model (EDM) – relates to Entity Relationship Model (Chen, 1976)
The EDM is a value-based conceptual model - it does not incorporate behaviours of any kind
Compare with UML, which expresses a conceptual model incorporating behaviour

3. Using an EDM EDM consists of:
Conceptual model
Logical model (storage in relational database)
Mapping between these
EDM can be used to generate C# (or VB) classes which can be used in an application
EF provides services for queries which work with C# objects
EF manages mappings from database data to object properties

4. Benefits of using an EDM
Data model in application is not tied to database schema
EDM allows developer to shape the data to suit the application, not the database
Database may be a shared or legacy db which cannot be modified by application developer
Normalisation or other optimisations in db may produce schema which does not match the application well
Compare with Linq to SQL, which is (essentially) designed to allow strongly typed querying of relational database

5. So, it’s an ORM then?
EF v1 allows building EDM by generating from database and manipulating in EDM Designer
Allows building of EDM and configuring mapping to databases
In both cases, EDM Designer generates code to represent data model in application
Not intended to take existing domain model and map to relational database
Not really an ORM, although it has many of the characteristics of one
EF v4 moves significantly towards being an ORM

6. EF v1 and persistence ignorance
EF v1 entity classes require a number of non-PI features, including:
Inherit from a certain base class - EntityObject
Only instantiate via a provided factory
Use specially provided datatypes, such as for collections - EntityCollection
Not PI!

7. EDM Mappings - Basic Map entities directly to tables
EDM has navigation properties
Can rename properties, exclude properties as required

8. EDM Mappings – Table Splitting
Two entities map onto the same table
Entities have one-to-one relationship

9. EDM Mappings – Inheritance (Table per Hierarchy)
Base class and derived classes all map to the same table
Discriminator field indicates which type to instantiate

10. EDM Mappings – Entity Splitting
One entity maps onto two separate tables
Tables must share a common key
Can access all properties in code without using navigation properties

11. EDM Mappings – Inheritance (Table per Type)
Base class and derived classes map to the separate tables
Tables must share a common key

12. EDM Mappings – Complex Types
Refactor set of properties of an entity to a complex type
Can use complex type in other entities
Complex type can only be persisted as part of an entity