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中文源码网。