Entity Framework 架构简介
The Entity Framework looks like a interesting technology which is more powerful and advanced than LINQ to SQL. Both technologies have a different kind of philosophy but several features have similar implementations. The EF is more than just an ORM (Object Relational Mapping) tool. It allows developers to query and manipulate data using a conceptual model instead of a physical storage model.
The ADO.NET Entity Framework is a layered framework which abstracts the relational schema of a database and presents a conceptual model.
Data Source : The bottom layer is the data which can be stored in one or many databases.
Data Providers : The data will be accessed by a ADO.NET data provider. At this moment only SQL Server is supported but in the near future there will be data providers for Oracle, MySQL, DB2, Firebird, Sybase, VistaDB, SQLite, ...
Entity Data Model (EDM) : The Entity Data Model consists of 3 parts :
- Conceptual schema definition language (CSDL) : Declare and define entities, associations, inheritance, ... Entity classes are generated from this schema.
- Store schema definition language (SSDL) : Metadata describing the storage container (=database) that persists data.
- Mapping specification language (MSL) : Maps the entities in the CSDL file to tables described in the SSDL file.
Entity Client : EntityClient is an ADO.NET managed provider that supports accessing data described in an Entity Data Model. It is similar to SQLClient, OracleClient and others. It provides several components like EntityCommand, EntityConnection and EntityTransaction.
Object Services : This component enables you to query, insert, update, and delete data, expressed as strongly-typed CLR objects that are instances of entity types. Object Services supports both Entity SQL and LINQ to Entities queries.
Entity SQL (ESQL) : Entity SQL is a derivative of Transact-SQL, designed to query and manipulate entities defined in the Entity Data Model. It supports inheritance and associations. Both Object Services components and Entity Client components can execute Entity SQL statements.
LINQ to Entities : This is a strong-typed query language for querying against entities defined in the Entity Data Model.
下图是来自微软MSDN的中文图片资料，表示了ADO.NET Entity Framework 体系结构:
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