【EF】EntityFramework DBFirst的使用

一、前言

       久闻EF大名，之前做C/S产品用的是Dapper对SqlLite进行ORM。然后接触公司授权系统后发现用的是EntityFramework对SQLSever进行ORM。授权系统里用的是DBFirst，增删查改使用Linq To Entity，觉得非常方便。本篇篇幅较短，老司机可直接略过

二、添加EF       

Step1：添加“新建项”，起个名称，添加ADO.NET实体数据模型；

Step2：选择模型类型，来自数据库的EF设计器；

Step3：选择数据连接，新建连接，选择要使用的数据库类型；默认SQLSever；

Step4：测试连接数据库；

Step5：选择EF版本；

Step6：选择要实体化的表，点击完成。

三、操作

       经过上述操作会产生三个文件：

1. EntityModel.Context.tt (上下文，所有class的DBSet集合都在这个文件下的.cs文件中)

2. EntityModel.tt       (每个表映射后的class都放在这个文件下面)

3. EntityModel.edmx (可视化的表设计器)

假设连接的数据库下有三个表：AgencyInfo,ContractInfo,CustomerInfo。那么EntityModel.tt下就会有三个对应的.cs文件：

//------------------------------------------------------------------------------
// <auto-generated>
//    This code was generated from a template.
//
//    Manual changes to this file may cause unexpected behavior in your application.
//    Manual changes to this file will be overwritten if the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

using System;
using System.Collections.Generic;

namespace HHH
{
    public partial class AgencyInfo
    {
        public System.Guid ID { get; set; }
        public string UnitName { get; set; }
        public string Phone { get; set; }
        public string Address { get; set; }
        public string comments { get; set; }
        public Nullable<System.DateTime> CreatTime { get; set; }
        public Nullable<int> ShowFlag { get; set; }
    }

}

//------------------------------------------------------------------------------
// <auto-generated>
//    This code was generated from a template.
//
//    Manual changes to this file may cause unexpected behavior in your application.
//    Manual changes to this file will be overwritten if the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

using System;
using System.Collections.Generic;

namespace HHH
{
    public partial class ContractInfo
    {
        public System.Guid ID { get; set; }
        public string Title { get; set; }
        public string Comment { get; set; }
        public Nullable<System.DateTime> CreateDate { get; set; }
    }

}

//------------------------------------------------------------------------------
// <auto-generated>
//    This code was generated from a template.
//
//    Manual changes to this file may cause unexpected behavior in your application.
//    Manual changes to this file will be overwritten if the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

using System;
using System.Collections.Generic;

namespace HHH
{
    public partial class CustomerInfo
    {
        public System.Guid ID { get; set; }
        public string Name { get; set; }
        public string ContactInfo { get; set; }
        public string Address { get; set; }
        public string Comments { get; set; }
        public string Email { get; set; }
        public string MobilePhone { get; set; }
        public string province { get; set; }
        public string City { get; set; }
        public string Type { get; set; }
        public Nullable<System.DateTime> CreateDate { get; set; }
    }

}

那么EntityModel.Context.tt是这样的：

//------------------------------------------------------------------------------
// <auto-generated>
//    This code was generated from a template.
//
//    Manual changes to this file may cause unexpected behavior in your application.
//    Manual changes to this file will be overwritten if the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

using System;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;

namespace HHH
{
    public partial class MyEntities: DbContext
    {
        public MyEntities()
            : base("name=MyEntities")
        {
        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            throw new UnintentionalCodeFirstException();
        }

        public DbSet<ContractInfo> ContractInfoes { get; set; }
        public DbSet<CustomerInfo> CustomerInfoes { get; set; }
        public DbSet<AgencyInfo> AgencyInfoes { get; set; }

    }
}

需要对表对象操作时，首先要：

private MyEntities dbContext = new MyEntities();

需要对哪个表操作，就dbContext.ContractInfoes或者dbContext.CustomerInfoes这样找到数据集合，然后用Linq去操作，最后别忘dbContext.SaveChanges()保存修改即可。

四、结尾

       明天再看看写点什么，保持学习进度，再过几天要去练车了