Entity Framework 学习整理(分播客整理)

在Entiry Framework中，我们有三种处理数据的方法：Database First,Model First,and Code First.这个教程中，我们使用Code First。关于这三种之间的差别以及具体该选择哪种，可以参考Entity Framework Development Workflows。

Database First

If you already have a database, the Entity Framework designer built into Visual Studio can automatically generate a data model that consists of classes and properties that correspond to existing database objects such as tables and columns. The information about your database structure (store schema), your data model (conceptual model), and the mapping between them is stored in XML in an .edmx file. The Entity Framework designer provides a graphical UI that you can use to display and edit the .edmx file.
Model First

If you don't have a database yet, you can begin by creating a model in an .edmx file by using the Entity Framework graphical designer in Visual Studio. When the model is finished, the Entity Framework designer can generate DDL (data definition language) statements to create the database. As in Database First, the .edmx file stores model and mapping information.
Code First

Whether you have an existing database or not, you can use the Entity Framework without using the designer or an .edmx file. If you don't have a database, you can code your own classes and properties that correspond to tables and columns. If you do have a database, Entity Framework tools can generate the classes and properties that correspond to existing tables and columns. The mapping between the store schema and the conceptual model represented by your code is handled by convention and by a special mapping API. If you let Code First create the database, you can use Code First Migrations to automate the process of deploying the database to production. Migrations can also automate the deployment of database schema changes to production when your data model changes.

Choose Code First for new development unless you want to use a graphical designer to model database objects and relationships. The Entity Framework designer only works with Database First and Model First. Before you choose Database First or Model First, however, consider how you want to handle updates to the data model after you create the database, and how you want to deploy the database and deploy updates to it. Code First Migrations automates the process of implementing and deploying database schema changes that result from data model changes. The advantages of Code First Migrations might outweigh the advantages of the Entity Framework designer.

数据库首先

    如果您已经有一个数据库，构建于Visual Studio中的实体框架设计器可以自动生成包括对应于现有的数据库类和属性对象，如表和列的数据模型。有关数据库的结构（存储模式），你的数据模型（概念模型），以及它们之间的映射信息存储在XML中。edmx文件。实体框架设计器提供了一个图形化的用户界面，你可以用它来显示和编辑。edmx文件。

    模型首先

    如果你没有一个数据库，但你可以通过在。 edmx文件创建一个模型首先使用实体框架图形设计在Visual Studio。当模型完成后，实体框架设计器可以生成DDL （数据定义语言）语句来创建数据库。由于在数据库一，。 edmx文件存储模型和映射信息。

    代码优先

    无论你是否有一个现有的数据库或没有，你可以使用实体框架不使用设计器或一个。 edmx文件。如果你没有一个数据库，你可以编写自己的类和属性的对应表和列。如果你有一个数据库中，实体框架工具可以生成对应于现有的表和列的类和属性。存储架构和代码所代表的概念模型之间的映射是通过约定并以特殊的映射的API来处理。如果你让代码首先创建数据库时，可以使用代码优先迁移到自动将数据库部署到生产过程中。迁移也可以自动的数据库架构更改部署到生产时，你的数据模型的变化。

选择代码第一次新的发展，除非你想使用一个图形设计模型的数据库对象和关系。实体框架设计只适用于数据库的第一和模型优先。在您选择数据库第一或型号不过，首先考虑你要如何处理更新的数据模型创建数据库之后，您希望如何部署数据库和部署更新它。代码优先迁移自动化实施和部署所造成的数据模型更改数据库架构更改的过程。代码优先迁移的优势可能会大于实体框架设计的优点。