Entity Framework教程-代码优先开发方式详解（Code First Development）

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2022年10月12日 发布。
2022年10月9日 从笔记迁移到博客。

EF Core代码优先开发方式详解（Code First Development）

说明#

记得先安装EF包，再使用

记得要给DbContext配置

默认构造函数

设置连接参数 否则不可以进行生成迁移

配置OnConfiguring方法

protected override void OnConfiguring(DbContextOptionsBuilder dbContextOptionsBuilder)

代码优先开发模式的步骤#

1.Create Database Context with connectionString

2.Create the model as a C# .Net class to generate a table.

3.Add public properties to the model with a data type and a name for fields.

4.Add the entity to the DBContext (if not already there) as DBSet where T is the type of your model. If the model is already in the DBContext, proceed to step 4.

5.Generate a new code-first migration to apply any and all of the modeled changes using the add-migration command .

6.Update the database using the update-database command .

直接定义上下文对象DbContext方式#

直接定义DbContext#

using System;
using ConsoleApp6.Models;
using Microsoft.EntityFrameworkCore;

namespace ConsoleApp6.Repository
{
    public class PandaDbContext: DbContext
    {
        /// <summary>
        /// 选项配置器
        /// </summary>
        private DbContextOptionsBuilder _dbContextOptionsBuilder;

        /// <summary>
        /// 构造函数，支持外部配置项
        /// </summary>
        /// <param name="options">配置项</param>
        public PandaDbContext(DbContextOptions options) :base(options)
        {

        }

        /// <summary>
        /// 默认构造函数
        /// </summary>
        public PandaDbContext() :base()
        {
            this._dbContextOptionsBuilder = new DbContextOptionsBuilder();
            this._dbContextOptionsBuilder.UseSqlServer("Server=192.168.1.18;Database=PandaTest;User Id=sa;Password=password;");
        }

        /// <summary>
        /// 配置上下文对象
        /// </summary>
        /// <param name="dbContextOptionsBuilder">选项配置器</param>
        protected override void OnConfiguring(DbContextOptionsBuilder dbContextOptionsBuilder)
        {
            if(!dbContextOptionsBuilder.IsConfigured)
            {
                dbContextOptionsBuilder.UseSqlServer("Server=192.168.1.18;Database=PandaTest;User Id=sa;Password=password;");
            }
        }

        public DbSet<Product> Products { get; set; }
    }
}

直接定义DbContext 带 配置类扩展#

记得先安装配置类的扩展

Microsoft.Extensions.Configuration

Microsoft.Extensions.Configuration.FileExtensions

Microsoft.Extensions.Configuration.Json

并新建appsettings.json文件用于保存配置信息

{
  "ConnectionStrings": {
    "Panda": "Server=192.168.1.18;Database=PandaTest;User Id=sa;Password=password;"
  }
}

Dbcontext代码：

using System;
using System.IO;
using ConsoleApp6.Models;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;

namespace ConsoleApp6.Repository
{
    public class PandaDbContext: DbContext
    {
        /// <summary>
        /// 选项配置器
        /// </summary>
        private DbContextOptionsBuilder _dbContextOptionsBuilder;

        /// <summary>
        /// 构造函数，支持外部配置项
        /// </summary>
        /// <param name="options">配置项</param>
        public PandaDbContext(DbContextOptions options) :base(options)
        {

        }

        /// <summary>
        /// 默认构造函数
        /// </summary>
        public PandaDbContext() :base()
        {
            this._dbContextOptionsBuilder = new DbContextOptionsBuilder();
            this._dbContextOptionsBuilder.UseSqlServer("Server=192.168.1.18;Database=PandaTest;User Id=sa;Password=password;");
        }

        /// <summary>
        /// 配置上下文对象
        /// </summary>
        /// <param name="dbContextOptionsBuilder">选项配置器</param>
        protected override void OnConfiguring(DbContextOptionsBuilder dbContextOptionsBuilder)
        {
            if(!dbContextOptionsBuilder.IsConfigured)
            {
                //新建配置项生成器
                ConfigurationBuilder builder = new ConfigurationBuilder();
                //配置项生成器设置
                builder.SetBasePath(Directory.GetCurrentDirectory())
                        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
                //构建配置
                var _configuration = builder.Build();
                //获得配置的具体字符串
                var cnstr = _configuration.GetConnectionString("Panda");
                //使用连接字符串
                dbContextOptionsBuilder.UseSqlServer(cnstr);
            }
        }

        public DbSet<Product> Products { get; set; }
    }
}

创建生成上下文DbContext对象的工厂类方式#

using System;
using ConsoleApp6.Repository;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;

namespace ConsoleApp6
{
    public class PandaDbContextFactory : IDesignTimeDbContextFactory<PandaDbContext>
    {
        public PandaDbContext CreateDbContext(string[] args)
        {
            var optionsBuilder = new DbContextOptionsBuilder<PandaDbContext>();
            optionsBuilder.UseSqlServer("Server=192.168.1.198;Database=PandaTest;User Id=sa;Password=Password;");

            return new PandaDbContext(optionsBuilder.Options);
        }
    }
}

EF代码优先开发方式详解（Code First Development）

概述#

使用CodeFirst方式进行开发，则可以不使用.edmx文件进行描述数据结构

而是使用手动定义类文件的方式定义数据结构

开发人员创建DbContext类和DbSet类型的继承对象来进行处理数据

与使用实体对象模型开发的对比#

Code First方式没法使用EF Designer设计工具

Code First方式中仅保留了实体对象模型开发中的DbContext和DbSet类型

使用Code First方式手动开发示例#

在项目中添加EF Nuget包

安装EF包

项目中新建一个Models文件夹

在Models文件夹下添加一个Product.cs类文件并写入Product类

在Models文件夹下进行PandaModel.cs文件并写入内容

注意：引入命名空间System.Data.Entity

配置App.config文件中的连接字符串

注意：除了手动配置连接信息外，还可以使用VS -【工具】-【连接到数据库】

<connectionStrings>
  <add name="pandaConnect" connectionString="data source=m1.panda666.com;initial catalog=PandaDatabase;persist security info=True;user id=sa;password=password;MultipleActiveResultSets=True;App=Entity Framework" providerName="System.Data.EntityClient"/>
</connectionStrings>

进行实际查询测试

using (PandaModel pandaModel = new PandaModel())
{
    var queryResult = from item in pandaModel.products
                        select item;
    foreach (Product item in queryResult)
    {
        Console.WriteLine("{0}-{1}-{2}",item.ProductId,item.ProductName,item.ProductType);
    }
}