MVC Code First 当实体类发生变化时，如何自动更新数据库表

下面做一个例子，Category是用户新建的一个实体类，然后添加一个字段，然后让数据库中的Category表也添加一个字段

1.Category.cs

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;

namespace BlogAppDAL.Entities
{
    public class Category
    {
        public int Id { get; set; }
        [Required]
        [StringLength(200)]
        public string CategoryName { get; set; }

        //public DateTime CreateDate { get; set; }
        public virtual ICollection<Blog> Blogs { get; set; }
        public Category()
        {
            Blogs = new HashSet<Blog>();
        }
    }
}

开始了添加一个字段，代码如下：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;

namespace BlogAppDAL.Entities
{
    public class Category
    {
        public int Id { get; set; }
        [Required]
        [StringLength(200)]
        public string CategoryName { get; set; }

        public DateTime CreateDate { get; set; }
        public virtual ICollection<Blog> Blogs { get; set; }
        public Category()
        {
            Blogs = new HashSet<Blog>();
        }
    }
}

在上下文当中写入下面的代码：

代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Entity;
using BlogAppDAL.Entities;
using System.Data.Entity.ModelConfiguration.Conventions;
using System.Data.Entity.Migrations;
using System.Data.Entity.Infrastructure;

namespace BlogAppDAL
{
    public class BlogAppContext : DbContext
    {
        public BlogAppContext()
            : base("name=BlogAppConn")
        {
            //自动创建表，如果Entity有改到就更新到表结构
            Database.SetInitializer<BlogAppContext>(new MigrateDatabaseToLatestVersion<BlogAppContext, ReportingDbMigrationsConfiguration>());
        }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); //表名为类名，不是带s的表名  //移除复数表名的契约
        }

        internal sealed class ReportingDbMigrationsConfiguration : DbMigrationsConfiguration<BlogAppContext>
        {
            public ReportingDbMigrationsConfiguration()
            {
                AutomaticMigrationsEnabled = true;//任何Model Class的修改將會直接更新DB
                AutomaticMigrationDataLossAllowed = true;
            }
        }
        
        public virtual DbSet<Blog> Blogs { get; set; }
        public virtual DbSet<Category> Categories { get; set; }
        public virtual DbSet<Comment> Comments { get; set; }
        public virtual DbSet<Role> Roles { get; set; }
        public virtual DbSet<User> Users { get; set; }
    }
}

 然后运行下程序就更新了数据库中的表了。而且连Migrations文件夹都不需要了