C # Blog Essay IX: The use of the EF framework

This chapter mainly describes the use of EF:

The acquisition of EF has been given in the previous chapter

Now you need to create a appmodelcontext

[Dbconfigurationtype (typeof(mysqldbconfiguration))]  Public Partial classAppmodelcontext:identitydbcontext<applicationuser, Customidentityrole, Guid, Customuserlogin, CustomUserRole, Customuserclaim>    {        StaticAppmodelcontext () {} Public StaticAppmodelcontext Create () {return NewAppmodelcontext (); }         PublicAppmodelcontext ():Base("name=db")        {        } PublicDbset<vote> votes {Get;Set; }  Public voidSetdebugoutput () { This. Database.Log = (s) = =Debug.WriteLine (s); }        protected Override voidonmodelcreating (Dbmodelbuilder modelBuilder) {Base.            Onmodelcreating (ModelBuilder); Modelbuilder.entity<ApplicationUser> (). Property (P = p.passwordhash). Hasmaxlength ( $); Modelbuilder.entity<ApplicationUser> (). Property (P = p.securitystamp). Hasmaxlength ( $); Modelbuilder.entity<ApplicationUser> (). Property (P = p.phonenumber). Hasmaxlength ( -); Modelbuilder.entity<CustomIdentityRole> (). Property (P = p.name). Hasmaxlength ( -); Modelbuilder.entity<ApplicationUser> (). Property (P = p.username). Hasmaxlength ( -); }

which

Public dbset<link> Links {get; set;}

This code is used to create a data table, and the structure of the data table is created in the link class.

About the content in the link class:

public class Link    {        [Key] public        int Id {get; set;}        [Stringlength ()]        [Display (name= "title")]        public string Title {get; set;}        [Stringlength (+)]        [URL]        [Display (name= "link")]        public string Url {get; set;}        Public linktype Type {get; set;}        public int SchoolID {get; set;}        Public linkstate linkstate {get; set;}        Public virtual ApplicationUser User {get; set;}        Public Guid UserId {get; set;}       Public linktype Type {get; set;}        public int TypeId {get; set;}    }

　　

It contains the primary key [key] string length [Stringlength (50)] filter rule [URL] and display name [Displays (name= "title")]

Public virtual ApplicationUser User {get; set;}        Public Guid UserId {get; set;}

is used to define foreign keys

After the table structure is defined

We add content to the context and then enter enable-migration in the package Manager Console

The migration folder is then automatically generated and then entered Add-migration Name

You can then enter update-database to update the database, each time you change the table structure add-migration Name and then update-database can update the table structure, but if there is data in the table and added a non-nullable field, it will be an error.

Using EF, you can map classes directly into a table structure, or you can load database data directly into objects, code error rates can be significantly reduced, code modification costs can be significantly reduced, and EF is a very good framework

C # Blog Essay IX: The use of the EF framework