Introduction to ef framework

EF The full name is EntityFramework .

  Entity Framework yes ADO.NET A set of technologies to support the development of data oriented software applications , It's one of Microsoft's ORM frame .
  ORM frame （Object Relational Mapping） Translated as object relational mapping .

Two 、EF Entity Framework overall architecture ：

Architecture components ：
  EDM（ Entity data model ）： EDM It's made up of three main parts - conceptual model , Map and store models .
  Conceptual Model： Conceptual models contain model classes and their relationships . This will be independent of your database table design .
  Storage Model： The storage model includes tables , View , Database design model of stored procedure and its relationship and key .
  Mapping： The mapping consists of information about how the conceptual model maps to the storage model .
  LINQ to Entities： LINQ to Entities Is a query language for writing queries against object models . It returns the entities defined in the conceptual model . You can use your... Here LINQ Skill .
  Entity SQL： Entity SQL Is another query language （ Only applicable to EF 6）, It's like LINQ to Entities equally . However , This is more than L2E It's a little harder , Developers need to learn alone .
  ObjectServices： Object service is the main entry point to access the data in the database and return it . Object services are responsible for implementing , This will be from the entity client data provider （ The next layer ） The process of converting the returned data into an entity object structure .
  Entity Client Data Provider： The main responsibility of this layer is to LINQ-to-Entities Or entity SQL The query is transformed into something that the underlying database can understand SQL Inquire about . It is associated with ADO.Net Data provider communication , and ADO.Net The data provider sends or retrieves data from the database .
  ADO.Net Data Provider： This layer uses standard ADO.Net Communicating with the database .

3、 ... and 、EF The advantages of （ And Comparison of ）

   If not ORM frame , We usually use it like this ADO.NET Database development ：

1. take ADO.NET The operations on the database are encapsulated in a class SqlHelper in
2. stay DAL Layer calls SqlHelper
3. Other layers call DAL Perform database operations

1.【 Logic 】 Business logic and data access logic are separated ;
2.【 New operation 】 EF: One connection , Execute more than one sql;SqlHelper Use general writing in , The connection cannot be released , use using, It will cause multiple connection resets ;
3.【 update operation 】 EF Automatic optimization , only update set Changing fields ,EF You can also easily update only Specified attributes of entities , Produced sql In the sentence set There will be fewer fields after ;
4.【 Smart tips 】 use linq, lamda expression There are smart tips , Wrong writing, but ; Write sql Statement string , transfer sqlhelper,sql If the statement is written incorrectly, it will be compiled and passed ;
5.【 Security 】 No prevention sql The trouble of injection ;
6.【 Database changes 】 Use EF, Switching is convenient ;
7.【 efficiency 】 Use EF Compared to using Ado.net High development efficiency ;
8.【 Readability 】 The code is more readable .

Four 、EF Three modes of framework

Database First（ Database first ）

   If you already have a database ,Visual Studio The built-in Entity Framework The designer can automatically generate a data model , The model consists of objects corresponding to existing databases （ See table and column ） Classes and properties of . About database structure , The information between the data model and the mapping is in XML The format is stored in .edmx In file . Entity Framework designer provides a visual interface , You can use it to display and edit .edmx file .

Model First（ Model first ）

   If you don't have a database , You can use Visual Studio Medium Entity Framework The designer is in .edmx Create a model in the file . When the model is finished , It can be executed .edmx File to create a database .

Code First（ Code first ）

   Whether you have a database or not , You can use Code First. If there is no database , You can write classes and properties corresponding to tables and columns . If there is a database , that Entity Framework You can generate classes and attributes corresponding to existing tables and columns . If you use Code First Create database , You can use “migration( transfer )” To deploy the database to the production environment . When the data model changes , Changes can be deployed to the production environment , Without changing the original data