ADO.Net Entity Framework

Entity framework has a full provider model. It supports not only SQL Server but also other database like Oracle, DB2, MySQL etc.

Most of the time L2S classes must be one-to-one with database objects e.g. Customer class can be mapped only with Customer table. Where as in Entity Framework you can map your domain class with multiple tables using various inheritance strategies like table per type (class) or table per hierarchy of classes etc.

You can have multiple modeling techniques using Entity Framework 4.1 like code first, model first or database first.

Microsoft has long term strategy to support and integrate Entity Framework with multiple Microsoft products.

EDM consist three main parts- Conceptual model, Mapping and Storage model.

Conceptual model is your model classes and their relationships. This will be independent from your database table design.

Storage model is your database design model which includes tables, views, stored procedures and their relationships and keys.

Mapping consist information about how your conceptual model is mapped to storage model.

LINQ to Entities is query language used to write queries against the object model. It returns entities which are defined in the conceptual model. You can use your LINQ skills here.

Entity SQL is again a query language same as LINQ to Entities. However it is little more difficult than L2E and also developer need to learn it separately.

Object service is a main entry point for accessing data from database and to return it back. Object service is responsible for materialization which is process of converting data returned from entity client data provider (next layer) to an entity object structure.

The main responsibility of this layer is to convert L2E or Entity SQL queries into SQL query which is understood by underlying database. It communicates with ADO.Net data provider which in turn sends or retrieves data from database.

This layer communicates with database using standard ADO.Net.

EDM designer represents your conceptual model. It consists Entities, associations & multiplicity between the entities. Initially it will exactly look like your database table structure but you can add or merge columns or remove columns which are not required by your application from this designer. Even you can add new object in this model which can have columns from different database tables from context menu as shown in above figure. Remember, whatever changes you do here it should be mapped with storage model. So you have to be careful while doing any changes in the designer.

EntityContainer is a wrapper for EntitySets and AssociationSets. It is critical entry point for querying the model.

EntitySet is a container for EntityType. It is set of same entitytype. You can think it like db table.

EntityType is a datatype in the model. You can see each EntityType for your conceptual model in XML. If you expand EntityType node in XML, you can see each properties and its type and other info.

AssociationSet defines the relation between each EntitySet.

Now, if you open designer.cs, you can see two main regions, Contexts and Entities. Expand contexts region. You can see partial class with suffix ‘entities’ and derived from ObjectContext class.

Each EntitySet in context class is a type of ObjectSet<> that wraps the entity. e.g. ObjectSet.

IObjectSet is a interface which gives collection like functionality. ObjectSet<> also implements IObjectSet. IObjectSet is useful in unit testing where you can create fake EntitySet (of type IObjectSet<>). We have used IObjectSet in our sample project.

Now if you expand ‘Entities’ region, you can see many partial classes that are derived from EntityObject. This classes are EntityTypes of you model.