Entity Framework之DB First方式详解

ef(entity framework的简称，下同)有三种方式，分别是：database first、 model first和code first。

下面是db first的方式：

1. 数据库库中存在两个表，一个是专业表，一个学生表，一个学生只能属于一个专业：

其中t_major是专业表，t_student是学生表，studentid是学号，majorid是专业id，t_major与t_student是一对多的关系。

2. 项目中添加数据库实体模型

因为之前没有配置过数据库连接，所以点击“新建库连接”，如果之前配置过数据库连接，可以直接从下拉列表中选择或者新建

选择需要生成的表/存储过程等

点击“完成”

这里会弹出如下图的窗口，然后选择确定(如果再弹出，也选择确定)，如果不小心点击了取消，可以在模型设计界面ctrl + s(保存的快捷键)，或如下图的操作，然后会弹出窗口，一直确定就行。

这里是使用mvc，所以添加一个控制器来测试（这里为了快速生成读写的控制器方法，选择“包含读/写操作的mvc5控制器”）

生成代码如下：

using system;
using system.collections.generic;
using system.linq;
using system.web;
using system.web.mvc;

namespace zhong.web.controllers
{
  public class studentcontroller : controller
  {
    // get: student
    public actionresult index()
    {
      return view();
    }

    // get: student/details/5
    public actionresult details(int id)
    {
      return view();
    }

    // get: student/create
    public actionresult create()
    {
      return view();
    }

    // post: student/create
    [httppost]
    public actionresult create(formcollection collection)
    {
      try
      {
        // todo: add insert logic here

        return redirecttoaction("index");
      }
      catch
      {
        return view();
      }
    }

    // get: student/edit/5
    public actionresult edit(int id)
    {
      return view();
    }

    // post: student/edit/5
    [httppost]
    public actionresult edit(int id, formcollection collection)
    {
      try
      {
        // todo: add update logic here

        return redirecttoaction("index");
      }
      catch
      {
        return view();
      }
    }

    // get: student/delete/5
    public actionresult delete(int id)
    {
      return view();
    }

    // post: student/delete/5
    [httppost]
    public actionresult delete(int id, formcollection collection)
    {
      try
      {
        // todo: add delete logic here

        return redirecttoaction("index");
      }
      catch
      {
        return view();
      }
    }
  }
}

同样的方法添加一个major控制器

using system;
using system.collections.generic;
using system.linq;
using system.web;
using system.web.mvc;

namespace zhong.web.controllers
{
  public class majorcontroller : controller
  {
    // get: major
    public actionresult index()
    {
      return view();
    }

    // get: major/details/5
    public actionresult details(int id)
    {
      return view();
    }

    // get: major/create
    public actionresult create()
    {
      return view();
    }

    // post: major/create
    [httppost]
    public actionresult create(formcollection collection)
    {
      try
      {
        // todo: add insert logic here

        return redirecttoaction("index");
      }
      catch
      {
        return view();
      }
    }

    // get: major/edit/5
    public actionresult edit(int id)
    {
      return view();
    }

    // post: major/edit/5
    [httppost]
    public actionresult edit(int id, formcollection collection)
    {
      try
      {
        // todo: add update logic here

        return redirecttoaction("index");
      }
      catch
      {
        return view();
      }
    }

    // get: major/delete/5
    public actionresult delete(int id)
    {
      return view();
    }

    // post: major/delete/5
    [httppost]
    public actionresult delete(int id, formcollection collection)
    {
      try
      {
        // todo: add delete logic here

        return redirecttoaction("index");
      }
      catch
      {
        return view();
      }
    }
  }
}

由于学生表majorid依赖于major表，所以需要先有专业，才能新增学生数据(这里不讨论是否合理)

编写逻辑代码，创建视图

using system;
using system.collections.generic;
using system.linq;
using system.web;
using system.web.mvc;
using zhong.web.models;

namespace zhong.web.controllers
{
  public class majorcontroller : controller
  {
    // get: major
    public actionresult index()
    {
      var majors = new efdbentities().t_major.tolist();
      return view(majors);
    }

    // get: major/details/5
    public actionresult details(int id)
    {
      var major = new efdbentities().t_major.find(id);
      if (major == null)
      {
        return content("参数错误");
      }
      return view(major);
    }

    // get: major/create
    public actionresult create()
    {
      return view();
    }

    // post: major/create
    [httppost]
    public actionresult create(t_major entity)
    {
      if (entity != null)
      {
        var entities = new efdbentities();
        entities.t_major.add(entity);
        entities.savechanges();
      }
      return redirecttoaction("index");
    }

    // get: major/edit/5
    public actionresult edit(int id)
    {
      var entity = new efdbentities().t_major.find(id);
      if (entity == null)
      {
        return content("参数错误");
      }
      return view(entity);
    }

    // post: major/edit/5
    [httppost]
    public actionresult edit(t_major entity)
    {
      if (entity == null)
      {
        return content("参数错误");
      }
      var entities = new efdbentities();
      #region 方式一 
      ////该方式一般是根据主键先读取数据，然后再逐个赋值，最后更新
      //var oldentity = entities.t_major.find(entity.id);
      //if (oldentity!=null)
      //{
      //  oldentity.name = entity.name;
      //  entities.savechanges();
      //}
      #endregion

      #region 方式二
      //该方式是直接将新的实体(可能是new出来的并且对主键等的属性赋值好了)附加到上下文，然后标记状态为修改modified
      entities.t_major.attach(entity);
      entities.entry(entity).state = system.data.entity.entitystate.modified;
      entities.savechanges();
      #endregion
      return redirecttoaction("index");
    }

    // get: major/delete/5
    public actionresult delete(int id)
    {
      var major = new efdbentities().t_major.find(id);
      return view(major);
    }

    // post: major/delete/5
    [httppost]
    public actionresult delete(int id, formcollection collection)
    {
      try
      {
        // todo: add delete logic here
        var entities = new efdbentities();
        var major = entities.t_major.find(id);
        entities.t_major.remove(major);
        entities.savechanges();
        return redirecttoaction("index");
      }
      catch
      {
        return view();
      }
    }
  }
}

添加专业：

专业列表：

同样实现学生控制器与视图：

using system;
using system.collections.generic;
using system.linq;
using system.web;
using system.web.mvc;
using zhong.web.models;

namespace zhong.web.controllers
{
  public class studentcontroller : controller
  {
    private efdbentities entities = new efdbentities();
    // get: student
    public actionresult index()
    {
      var students = entities.t_student.tolist();
      return view(students);
    }

    // get: student/details/5
    public actionresult details(int id)
    {
      var student = entities.t_student.find(id);
      return view(student);
    }

    // get: student/create
    public actionresult create()
    {
      viewdata["majorid"] = entities.t_major.select(m => new selectlistitem { text = m.name, value = m.id.tostring() });
      return view();
    }

    // post: student/create
    [httppost]
    public actionresult create(t_student entity)
    {
      entities.t_student.add(entity);
      entities.savechanges();
      return redirecttoaction("index");
    }

    // get: student/edit/5
    public actionresult edit(int id)
    {
      var student = entities.t_student.find(id);
      viewdata["majorid"] = entities.t_major.select(m => new selectlistitem { text = m.name, value = m.id.tostring() });
      return view(student);
    }

    // post: student/edit/5
    [httppost]
    public actionresult edit(t_student entity)
    {
      if (entity == null)
      {
        return content("参数错误");
      }
      entities.t_student.attach(entity);
      entities.entry(entity).state = system.data.entity.entitystate.modified;
      entities.savechanges();
      return redirecttoaction("index");
    }

    // get: student/delete/5
    public actionresult delete(int id)
    {
      var student = entities.t_student.find(id);
      return view(student);
    }

    // post: student/delete/5
    [httppost]
    public actionresult delete(int id, formcollection collection)
    {
      var student = entities.t_student.find(id);
      entities.t_student.remove(student);
      entities.savechanges();
      return redirecttoaction("index");
    }
  }
}

添加学生时，报错如下：

于是在控制器中增加如下代码：

刷新页面：

编辑：

删除：

列表：

在majorcontroller中有介绍ef的两种更新方式。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。