实验环境：

window10 64位
vs2019 Enterprise 16.7.4
.netcoreapp3.1
EntityFrameworkCore 3.1.9
sqlserver 2008 R2

实验目的：

验证EntityFrameworkCore的增删改查

说明：

使用“EntityFrameworkCore”是有两种方式：DBFirst和CodeFirst，小型项目可以用CodeFirst，大型项目一般用DBFirst，这里主要采用DBFirst

下面采用DBFirst实验，最后说明CodeFirst

一、准备数据库

新建表student、book、teacher、studentbook、studentinfo

他们之间存在1对多、多对多的关系：

student和book通过studentbook实现多对多
studentinfo与student是一对一
book与teacher是一对多

建库脚本如下：

--***************先清空具有外键的表:studentbook/studentinfo/teacher ***********
if exists (select 1  
            from  sysobjects  
           where  id = object_id('studentbook')  
            and   type = 'U')  
begin
   drop table studentbook  
   print '已删除表:studentbook'
end
go

if exists (select 1  
            from  sysobjects  
           where  id = object_id('studentinfo')  
            and   type = 'U')  
begin
   drop table studentinfo  
   print '已删除表:studentinfo'
end
go 

if exists (select 1  
            from  sysobjects  
           where  id = object_id('teacher')  
            and   type = 'U')  
begin
   drop table teacher  
   print '已删除表:teacher'
end
go 

--**************************************

--****************<book>**************
if exists (select 1  
            from  sysobjects  
           where  id = object_id('book')  
            and   type = 'U')  
begin
   drop table book  
   print '已删除表:book'
end
go 

create table [book] (
    [id] int not null   unique,
    [name] varchar(50)    
)

 
ALTER TABLE [book] ADD CONSTRAINT PK_gene_book_id PRIMARY KEY(id)
 



print '已创建:book'
go
--****************</book>**************

--****************<student>**************
if exists (select 1  
            from  sysobjects  
           where  id = object_id('student')  
            and   type = 'U')  
begin
   drop table student  
   print '已删除表:student'
end
go 

create table [student] (
    [id] int not null   unique,
    [name] varchar(50) not null   ,
    [addr] varchar(500)    ,
    [birth] datetime    ,
    [img] image    
)

 
ALTER TABLE [student] ADD CONSTRAINT PK_gene_student_id PRIMARY KEY(id)
 



print '已创建:student'
go
--****************</student>**************

--****************<studentbook>**************
create table [studentbook] (
    [sid] int not null   ,
    [bookid] int not null   
)

 
ALTER TABLE [studentbook] ADD CONSTRAINT PK_gene_studentbook_sid_bookid PRIMARY KEY([sid],[bookid])
 

--************外键约束<FK_userbook_userbook>*****************
ALTER TABLE studentbook ADD CONSTRAINT FK_userbook_userbook FOREIGN KEY(sid) REFERENCES test.dbo.student (id) ON DELETE NO ACTION ON UPDATE NO ACTION
--************外键约束</FK_userbook_userbook>*****************

--************外键约束<FK_userbook_userbook1>*****************
ALTER TABLE studentbook ADD CONSTRAINT FK_userbook_userbook1 FOREIGN KEY(bookid) REFERENCES test.dbo.book (id) ON DELETE NO ACTION ON UPDATE NO ACTION
--************外键约束</FK_userbook_userbook1>*****************



print '已创建:studentbook'
go
--****************</studentbook>**************

--****************<studentinfo>**************
create table [studentinfo] (
    [sid] int not null   unique,
    [indate] datetime    ,
    [type] int    ,
    [desc] varchar(500)    
)

 
ALTER TABLE [studentinfo] ADD CONSTRAINT PK_gene_studentinfo_sid PRIMARY KEY(sid)
 

--************外键约束<FK_studentinfo_student>*****************
ALTER TABLE studentinfo ADD CONSTRAINT FK_studentinfo_student FOREIGN KEY(sid) REFERENCES test.dbo.student (id) ON DELETE NO ACTION ON UPDATE NO ACTION
--************外键约束</FK_studentinfo_student>*****************



print '已创建:studentinfo'
go
--****************</studentinfo>**************
--****************<teacher>**************


create table [teacher] (
    [id] int not null   unique,
    [name] varchar(50) not null   ,
    [bid] int not null   
)

 
ALTER TABLE [teacher] ADD CONSTRAINT PK_gene_teacher_id PRIMARY KEY(id)
 

--************外键约束<FK_teacher_teacher>*****************
ALTER TABLE teacher ADD CONSTRAINT FK_teacher_teacher FOREIGN KEY(bid) REFERENCES test.dbo.book (id) ON DELETE NO ACTION ON UPDATE NO ACTION
--************外键约束</FK_teacher_teacher>*****************



print '已创建:teacher'
go
--****************</teacher>**************

二、准备工程

打开vs2019，新建两个.netcore控制台项目如下：

.netcore入门4：Microsoft.EntityFrameworkCore操作笔记一、准备数据库二、准备工程三、从数据库生成模型代码四、修改生成的testContext，增加日志输出五、编写增删改查代码六、测试效果七、codefirst模式八、说一下codefirst模式和dbfirst模式

编辑dbfirst工程，添加EntityFrameworkCore包：

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.1.10" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="3.1.10">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
    </PackageReference>
    <PackageReference Include="Microsoft.Extensions.Logging.Console" Version="3.1.10" />
    <PackageReference Include="Microsoft.Extensions.Logging.Debug" Version="3.1.10" />
  </ItemGroup>
</Project>

或者使用vs安装如下：

注意：上面包的作用

Microsoft.EntityFrameworkCore.SqlServer：efcore操作sqlserver；

Microsoft.EntityFrameworkCore.Tools：efcore的工具包，可用来做dbfirst/codefirst

Microsoft.Extensions.Logging.Console：将日志输出到控制台

Microsoft.Extensions.Logging.Debug：将日志输出到vs的调试窗口

三、从数据库生成模型代码

打开包管理控制台窗口：

执行命令：

Scaffold-DbContext "Data Source = .;Initial Catalog = test;User Id = sa;Password = 123456;" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models

完成后观察项目中自动生成了的代码：

Book.cs:

using System;
using System.Collections.Generic;

namespace dbfirst.Models
{
    public partial class Book
    {
        public Book()
        {
            Studentbook = new HashSet<Studentbook>();
            Teacher = new HashSet<Teacher>();
        }

        public int Id { get; set; }
        public string Name { get; set; }

        public virtual ICollection<Studentbook> Studentbook { get; set; }
        public virtual ICollection<Teacher> Teacher { get; set; }
    }
}

Student.cs

using System;
using System.Collections.Generic;

namespace dbfirst.Models
{
    public partial class Student
    {
        public Student()
        {
            Studentbook = new HashSet<Studentbook>();
        }

        public int Id { get; set; }
        public string Name { get; set; }
        public string Addr { get; set; }
        public DateTime? Birth { get; set; }
        public byte[] Img { get; set; }

        public virtual Studentinfo Studentinfo { get; set; }
        public virtual ICollection<Studentbook> Studentbook { get; set; }
    }
}

Teacher:

using System;
using System.Collections.Generic;

namespace dbfirst.Models
{
    public partial class Teacher
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Bid { get; set; }

        public virtual Book B { get; set; }
    }
}

Studentbook.cs:

using System;
using System.Collections.Generic;

namespace dbfirst.Models
{
    public partial class Studentbook
    {
        public int Sid { get; set; }
        public int Bookid { get; set; }

        public virtual Book Book { get; set; }
        public virtual Student S { get; set; }
    }
}

Studentinfo.cs:

using System;
using System.Collections.Generic;

namespace dbfirst.Models
{
    public partial class Studentinfo
    {
        public int Sid { get; set; }
        public DateTime? Indate { get; set; }
        public int? Type { get; set; }
        public string Desc { get; set; }

        public virtual Student S { get; set; }
    }
}

testContext.cs:

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata;

namespace dbfirst.Models
{
    public partial class testContext : DbContext
    {
        public testContext()
        {
        }

        public testContext(DbContextOptions<testContext> options)
            : base(options)
        {
        }

        public virtual DbSet<Book> Book { get; set; }
        public virtual DbSet<Student> Student { get; set; }
        public virtual DbSet<Studentbook> Studentbook { get; set; }
        public virtual DbSet<Studentinfo> Studentinfo { get; set; }
        public virtual DbSet<Teacher> Teacher { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
#warning To protect potentially sensitive information in your connection string, you should move it out of source code. See http://go.microsoft.com/fwlink/?LinkId=723263 for guidance on storing connection strings.
                optionsBuilder.UseSqlServer("Data Source = .;Initial Catalog = test;User Id = sa;Password = 123456;");
            }
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.HasAnnotation("ProductVersion", "2.2.6-servicing-10079");

            modelBuilder.Entity<Book>(entity =>
            {
                entity.ToTable("book");

                entity.HasIndex(e => e.Id)
                    .HasName("UQ__book__3213E83ED78FF78C")
                    .IsUnique();

                entity.Property(e => e.Id)
                    .HasColumnName("id")
                    .ValueGeneratedNever();

                entity.Property(e => e.Name)
                    .HasColumnName("name")
                    .HasMaxLength(50)
                    .IsUnicode(false);
            });

            modelBuilder.Entity<Student>(entity =>
            {
                entity.ToTable("student");

                entity.HasIndex(e => e.Id)
                    .HasName("UQ__student__3213E83E18FC0D17")
                    .IsUnique();

                entity.Property(e => e.Id)
                    .HasColumnName("id")
                    .ValueGeneratedNever();

                entity.Property(e => e.Addr)
                    .HasColumnName("addr")
                    .HasMaxLength(500)
                    .IsUnicode(false);

                entity.Property(e => e.Birth)
                    .HasColumnName("birth")
                    .HasColumnType("datetime");

                entity.Property(e => e.Img)
                    .HasColumnName("img")
                    .HasColumnType("image");

                entity.Property(e => e.Name)
                    .IsRequired()
                    .HasColumnName("name")
                    .HasMaxLength(50)
                    .IsUnicode(false);
            });

            modelBuilder.Entity<Studentbook>(entity =>
            {
                entity.HasKey(e => new { e.Sid, e.Bookid })
                    .HasName("PK_gene_studentbook_sid_bookid");

                entity.ToTable("studentbook");

                entity.Property(e => e.Sid).HasColumnName("sid");

                entity.Property(e => e.Bookid).HasColumnName("bookid");

                entity.HasOne(d => d.Book)
                    .WithMany(p => p.Studentbook)
                    .HasForeignKey(d => d.Bookid)
                    .OnDelete(DeleteBehavior.ClientSetNull)
                    .HasConstraintName("FK_userbook_userbook1");

                entity.HasOne(d => d.S)
                    .WithMany(p => p.Studentbook)
                    .HasForeignKey(d => d.Sid)
                    .OnDelete(DeleteBehavior.ClientSetNull)
                    .HasConstraintName("FK_userbook_userbook");
            });

            modelBuilder.Entity<Studentinfo>(entity =>
            {
                entity.HasKey(e => e.Sid)
                    .HasName("PK_gene_studentinfo_sid");

                entity.ToTable("studentinfo");

                entity.HasIndex(e => e.Sid)
                    .HasName("UQ__studenti__DDDFDD370E427379")
                    .IsUnique();

                entity.Property(e => e.Sid)
                    .HasColumnName("sid")
                    .ValueGeneratedNever();

                entity.Property(e => e.Desc)
                    .HasColumnName("desc")
                    .HasMaxLength(500)
                    .IsUnicode(false);

                entity.Property(e => e.Indate)
                    .HasColumnName("indate")
                    .HasColumnType("datetime");

                entity.Property(e => e.Type).HasColumnName("type");

                entity.HasOne(d => d.S)
                    .WithOne(p => p.Studentinfo)
                    .HasForeignKey<Studentinfo>(d => d.Sid)
                    .OnDelete(DeleteBehavior.ClientSetNull)
                    .HasConstraintName("FK_studentinfo_student");
            });

            modelBuilder.Entity<Teacher>(entity =>
            {
                entity.ToTable("teacher");

                entity.HasIndex(e => e.Id)
                    .HasName("UQ__teacher__3213E83EAD9D5139")
                    .IsUnique();

                entity.Property(e => e.Id)
                    .HasColumnName("id")
                    .ValueGeneratedNever();

                entity.Property(e => e.Bid).HasColumnName("bid");

                entity.Property(e => e.Name)
                    .IsRequired()
                    .HasColumnName("name")
                    .HasMaxLength(50)
                    .IsUnicode(false);

                entity.HasOne(d => d.B)
                    .WithMany(p => p.Teacher)
                    .HasForeignKey(d => d.Bid)
                    .OnDelete(DeleteBehavior.ClientSetNull)
                    .HasConstraintName("FK_teacher_teacher");
            });
        }
    }
}

四、修改生成的 `testContext` ，增加日志输出

修改

testContext

的

OnConfiguring

方法如下：

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    if (!optionsBuilder.IsConfigured)
    {
#warning To protect potentially sensitive information in your connection string, you should move it out of source code. See http://go.microsoft.com/fwlink/?LinkId=723263 for guidance on storing connection strings.
        optionsBuilder.UseSqlServer("Data Source = .;Initial Catalog = test;User Id = sa;Password = 123456;");

        //准备依赖容器
        var services = new ServiceCollection();
        services.AddLogging(builder =>
        {
            builder.ClearProviders();
            //将日志输出到控制台
            builder.AddConsole();
            //将日志输出到vs的调试窗口
            builder.AddDebug();
        });
        var provider = services.BuildServiceProvider();
        //从容器中拿到日志工厂
        var loggerFactory = provider.GetRequiredService<ILoggerFactory>();
        //启用efcore的日志记录
        optionsBuilder.UseLoggerFactory(loggerFactory);
        //使efcore的日志中输出敏感信息(含参数化值)
        optionsBuilder.EnableSensitiveDataLogging(true);
    }
}

五、编写增删改查代码

只需修改Program.cs即可：

using System;
using System.Text;
using System.Threading.Tasks;
using dbfirst.Models;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;

namespace dbfirst
{
    class Program
    {
        static void Main(string[] args)
        {
            //TestAdd();
            //TestQuery();
            //TestUpdate();
            //TestDelete();
            Console.WriteLine("Hello World!");
        }

        private static void TestDelete()
        {
            using (testContext db = new testContext())
            {
                var id = db.Student.Where(i => i.Name == "小明").Select(i => i.Id).FirstOrDefault();
                db.Studentbook.RemoveRange(db.Studentbook.Where(i => i.Sid == id));
                db.SaveChanges();
            }
        }

        private static void TestUpdate()
        {
            using (testContext db = new testContext())
            {
                Book b = db.Book.Where(i => i.Name == "外语").FirstOrDefault();
                if (b != null)
                {
                    b.Name = "英语";
                }
                db.SaveChanges();
            }
        }

        private static void TestQuery()
        {
            using (testContext db = new testContext())
            {
                var set = (from stu in db.Student join b in db.Studentbook on stu.Id equals b.Sid join book in db.Book on b.Bookid equals book.Id where stu.Name.Contains("小") select new { StuName = stu.Name, stuId = stu.Id, bookName = book.Name, bookId = book.Id });
                var list = set.ToList();
                foreach (var i in list)
                {
                    Console.WriteLine(i.bookId + ":" + i.bookName + "," + i.StuName + ":" + i.stuId);
                }
            }

        }
        
        private static void TestAdd()
        {
            using (testContext db = new testContext())
            {
                //创建四名学生(小明、小红、小刚、小军)
                Student xiaoming = new Student()
                {
                    Id = 1,
                    Name = "小明",
                    Birth = DateTime.Parse("1995-02-03"),
                    Addr = "天民路28号",
                    Img = Encoding.UTF8.GetBytes("哈哈 this is a 测试")
                };
                Student xiaohong = new Student()
                {
                    Id = 2,
                    Name = "小红",
                    Birth = DateTime.Parse("1998-07-03"),
                    Addr = "顺丰路28号",
                    Img = Encoding.UTF8.GetBytes("哈哈 this is a 测试")
                };
                Student xiaogang = new Student()
                {
                    Id = 3,
                    Name = "小刚",
                    Birth = DateTime.Parse("1994-07-03"),
                    Addr = "江山28号",
                    Img = Encoding.UTF8.GetBytes("哈哈 this is a 测试")
                };
                Student xiaojun = new Student()
                {
                    Id = 4,
                    Name = "小军",
                    Birth = DateTime.Parse("1995-07-03"),
                    Addr = "江山29号",
                    Img = Encoding.UTF8.GetBytes("哈哈 this is a 测试")
                };
                //创建三门课(语文、数学、外语)
                Book yuwen = new Book()
                {
                    Id = 1,
                    Name = "语文"
                };
                Book shuxue = new Book()
                {
                    Id = 2,
                    Name = "数学"
                };
                Book waiyu = new Book()
                {
                    Id = 3,
                    Name = "外语"
                };
                //创建三个老师分别教三门课
                Teacher yuwenlaoshi = new Teacher()
                {
                    Id = 1,
                    Name = "语文老师",
                    Bid = yuwen.Id
                };
                Teacher shuxuelaoshi = new Teacher()
                {
                    Id = 2,
                    Name = "数学老师",
                    Bid = shuxue.Id
                };
                Teacher waiyulaoshi = new Teacher()
                {
                    Id = 3,
                    Name = "外语老师",
                    Bid = waiyu.Id
                };
                //给三个学生都选择语数外三门课
                Studentbook xiaohongyuwen = new Studentbook()
                {
                    Bookid = yuwen.Id,
                    Sid = xiaohong.Id
                };
                Studentbook xiaohongshuxue = new Studentbook()
                {
                    Bookid = shuxue.Id,
                    Sid = xiaohong.Id
                };
                Studentbook xiaohongwaiyu = new Studentbook()
                {
                    Bookid = waiyu.Id,
                    Sid = xiaohong.Id
                };
                Studentbook xiaomingyuwen = new Studentbook()
                {
                    Bookid = yuwen.Id,
                    Sid = xiaoming.Id
                };
                Studentbook xiaomingshuxue = new Studentbook()
                {
                    Bookid = shuxue.Id,
                    Sid = xiaoming.Id
                };
                Studentbook xiaomingwaiyu = new Studentbook()
                {
                    Bookid = waiyu.Id,
                    Sid = xiaoming.Id
                };
                Studentbook xiaogangyuwen = new Studentbook()
                {
                    Bookid = yuwen.Id,
                    Sid = xiaogang.Id
                };
                Studentbook xiaogangshuxue = new Studentbook()
                {
                    Bookid = shuxue.Id,
                    Sid = xiaogang.Id
                };
                Studentbook xiaogangwaiyu = new Studentbook()
                {
                    Bookid = waiyu.Id,
                    Sid = xiaogang.Id
                };
                Studentbook xiaojunyuwen = new Studentbook()
                {
                    Bookid = yuwen.Id,
                    Sid = xiaojun.Id
                };
                Studentbook xiaojunshuxue = new Studentbook()
                {
                    Bookid = shuxue.Id,
                    Sid = xiaojun.Id
                };
                Studentbook xiaojunwaiyu = new Studentbook()
                {
                    Bookid = waiyu.Id,
                    Sid = xiaojun.Id
                };
                //给四名同学添加扩展信息
                Studentinfo xiaominginfo = new Studentinfo()
                {
                    Sid = xiaoming.Id,
                    Indate = DateTime.Now,
                    Type = 1,
                    Desc = "一段描述"
                };
                Studentinfo xiaojuninfo = new Studentinfo()
                {
                    Sid = xiaojun.Id,
                    Indate = DateTime.Now,
                    Type = 1,
                    Desc = "一段描述"
                };
                Studentinfo xiaohonginfo = new Studentinfo()
                {
                    Sid = xiaohong.Id,
                    Indate = DateTime.Now,
                    Type = 1,
                    Desc = "一段描述"
                };
                Studentinfo xiaoganginfo = new Studentinfo()
                {
                    Sid = xiaogang.Id,
                    Indate = DateTime.Now,
                    Type = 1,
                    Desc = "一段描述"
                };
                db.AddRange(xiaoming, xiaogang, xiaojun, xiaohong);
                db.AddRange(yuwen, waiyu, shuxue);
                db.AddRange(yuwenlaoshi, shuxuelaoshi, waiyulaoshi);
                db.AddRange(xiaominginfo, xiaoganginfo, xiaojuninfo, xiaohonginfo);
                db.AddRange(xiaomingyuwen, xiaomingshuxue, xiaomingwaiyu);
                db.AddRange(xiaohongyuwen, xiaohongshuxue, xiaohongwaiyu);
                db.AddRange(xiaogangyuwen, xiaogangshuxue, xiaogangwaiyu);
                db.AddRange(xiaojunyuwen, xiaojunshuxue, xiaojunwaiyu);
                db.SaveChanges();

            }
        }
    }
}

六、测试效果

先运行“TestAdd”添加数据，观察如下：

控制台日志输出如下：

接下来依次运行：

TestQuery

、

TestUpdate

、

TestDelete

即可。

七、codefirst模式

在dbfirst实验的基础上，完成codefirst实验，修改

codefirst

工程：

添加nuget包（和dbfirst一样即可）
将 dbfirst工程 中的代码拷贝到 codefirst工程 中，并将命名空间修改为 codefirst
修改数据库为 test2 （在 testContext.cs 中修改）
最终效果如下：

.netcore入门4：Microsoft.EntityFrameworkCore操作笔记一、准备数据库二、准备工程三、从数据库生成模型代码四、修改生成的testContext，增加日志输出五、编写增删改查代码六、测试效果七、codefirst模式八、说一下codefirst模式和dbfirst模式

.netcore入门4：Microsoft.EntityFrameworkCore操作笔记一、准备数据库二、准备工程三、从数据库生成模型代码四、修改生成的testContext，增加日志输出五、编写增删改查代码六、测试效果七、codefirst模式八、说一下codefirst模式和dbfirst模式
将 codefirst 设为启动程序
在包管理平台中执行 Add-Migration init 命令，如下所示：

.netcore入门4：Microsoft.EntityFrameworkCore操作笔记一、准备数据库二、准备工程三、从数据库生成模型代码四、修改生成的testContext，增加日志输出五、编写增删改查代码六、测试效果七、codefirst模式八、说一下codefirst模式和dbfirst模式
可看到生成的迁移类和快照
在包管理平台中执行 Update-Database 命令，如下所示：

.netcore入门4：Microsoft.EntityFrameworkCore操作笔记一、准备数据库二、准备工程三、从数据库生成模型代码四、修改生成的testContext，增加日志输出五、编写增删改查代码六、测试效果七、codefirst模式八、说一下codefirst模式和dbfirst模式
观察数据库test2：

.netcore入门4：Microsoft.EntityFrameworkCore操作笔记一、准备数据库二、准备工程三、从数据库生成模型代码四、修改生成的testContext，增加日志输出五、编写增删改查代码六、测试效果七、codefirst模式八、说一下codefirst模式和dbfirst模式

可以看到，自动建了数据库test2并且建好了表结构

拷贝dbfirst的Program.cs的代码到codefirst中去（注意：修改命名空间），依次执行测试代码即可。

八、说一下codefirst模式和dbfirst模式

首先说明dbfirst就是先建好数据库，然后使用命令

Scaffold-DbContext "Data Source = .;Initial Catalog = test;User Id = sa;Password = 123456;" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models

将指定的数据库中所有表生成代码到指定的工程目录中去，这就结束了。

再看一下codefirst模式，在这种模式下最后不要在数据库客户端修改数据库的结构，如果想修改数据库结构，就先改代码，然后让EntityFrameworkCore工具自动去执行修改数据库结构。

codefirst一般操作流程如下：

工程中建好实体model和dbcontext（注意工程需要是可执行程序）
在包管理控制台中使用 Add-Migration init 命令生成用来执行迁移操作的代码(init是每次迁移的一个标识，可自定义)
如果此时数据库结构有改动需要再次修改工程的实体model和dbcontext，那么你可以执行 Remove-Migration 命令直接将最近的依次迁移代码删除掉
确认工程的实体model和dbcontext没问题并且生成的迁移代码没有问题，那么可以执行命令 Update-Database 将迁移代码应用到数据库中，此时codefirst也就完成了。

codefirst涉及到的命令说明：

Add-Migration [自定义标识] ，示例： Add-Migration init
（注：这个过程不需要和数据库交互）

初次使用将根据DbContext找到对应的实体类，然后根据实体类生成“20190910082556_init”迁移类，这个类里面记录的是要创建的表和字段，并且生成此时这个表的快照（根据实体类生成）

非初次运行这个命令的时候，将对比当前的实体类和这个表的快照，然后根据对比的结果生成迁移类并更新快照
Update-Database

首先连接数据库获取数据库已经迁移过的版本号（表：__EFMigrationsHistory中记录历史更新记录），然后对比当前工程下的迁移代码的版本号，如果发现还有未执行的迁移代码那么就执行迁移代码，如果没有的话就不执行
Remove-Migration

首先连接数据库获取数据库已经迁移过的版本号，然后对比当前工程最新的迁移类的版本号，如果数据库中没有记录这个版本号表示迁移类还未执行，那么直接删除掉这个迁移类，并更新快照，如果发现已经执行了这个迁移类那么就报错提示“已经更新到数据库了”
Get-DbContext

获取当前工程的上下文环境
Script-Migration

将当前的迁移代码翻译成sql脚本

一、准备数据库

二、准备工程

三、从数据库生成模型代码

四、修改生成的 `testContext` ，增加日志输出

五、编写增删改查代码

六、测试效果

七、codefirst模式

八、说一下codefirst模式和dbfirst模式

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一、准备数据库

二、准备工程

三、从数据库生成模型代码

四、 修改生成的 testContext ，增加日志输出

五、编写增删改查代码

六、测试效果

七、codefirst模式

八、说一下codefirst模式和dbfirst模式

继续阅读

四、修改生成的 `testContext` ，增加日志输出