Entity Framework之DB First方式詳解

更新時(shí)間：2017年07月24日 15:57:42 作者：zhjchhahaha

這篇文章主要為大家詳細(xì)介紹了Entity Framework三種方式之一DataBase First，具有一定的參考價(jià)值，感興趣的小伙伴們可以參考一下

EF(Entity Framework的簡稱，下同)有三種方式，分別是：DataBase First、 Model First和Code First。

下面是Db First的方式：

1. 數(shù)據(jù)庫庫中存在兩個(gè)表，一個(gè)是專業(yè)表，一個(gè)學(xué)生表，一個(gè)學(xué)生只能屬于一個(gè)專業(yè)：

其中T_Major是專業(yè)表，T_Student是學(xué)生表，StudentId是學(xué)號(hào)，MajorId是專業(yè)Id，T_Major與T_Student是一對多的關(guān)系。

2. 項(xiàng)目中添加數(shù)據(jù)庫實(shí)體模型

因?yàn)橹皼]有配置過數(shù)據(jù)庫連接，所以點(diǎn)擊“新建庫連接”，如果之前配置過數(shù)據(jù)庫連接，可以直接從下拉列表中選擇或者新建

選擇需要生成的表/存儲(chǔ)過程等

點(diǎn)擊“完成”

這里會(huì)彈出如下圖的窗口，然后選擇確定(如果再彈出，也選擇確定)，如果不小心點(diǎn)擊了取消，可以在模型設(shè)計(jì)界面Ctrl + S(保存的快捷鍵)，或如下圖的操作，然后會(huì)彈出窗口，一直確定就行。

這里是使用MVC，所以添加一個(gè)控制器來測試（這里為了快速生成讀寫的控制器方法，選擇“包含讀/寫操作的MVC5控制器”）

生成代碼如下：

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();
      }
    }
  }
}

同樣的方法添加一個(gè)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();
      }
    }
  }
}

由于學(xué)生表MajorId依賴于Major表，所以需要先有專業(yè)，才能新增學(xué)生數(shù)據(jù)(這里不討論是否合理)

編寫邏輯代碼，創(chuàng)建視圖

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("參數(shù)錯(cuò)誤");
      }
      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("參數(shù)錯(cuò)誤");
      }
      return View(entity);
    }

    // POST: Major/Edit/5
    [HttpPost]
    public ActionResult Edit(T_Major entity)
    {
      if (entity == null)
      {
        return Content("參數(shù)錯(cuò)誤");
      }
      var entities = new EFDbEntities();
      #region 方式一 
      ////該方式一般是根據(jù)主鍵先讀取數(shù)據(jù)，然后再逐個(gè)賦值，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
      //該方式是直接將新的實(shí)體(可能是new出來的并且對主鍵等的屬性賦值好了)附加到上下文，然后標(biāo)記狀態(tài)為修改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();
      }
    }
  }
}

添加專業(yè)：

專業(yè)列表：

同樣實(shí)現(xiàn)學(xué)生控制器與視圖：

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("參數(shù)錯(cuò)誤");
      }
      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");
    }
  }
}

添加學(xué)生時(shí)，報(bào)錯(cuò)如下：