Entity Framework之DB First方式_ZenDei技術網路在線

EF(Entity Framework的簡稱，下同)有三種方式，分別是：DataBase First、 Model First和Code First。下麵是Db First的方式： 1. 資料庫庫中存在兩個表，一個是專業表，一個學生表，一個學生只能屬於一個專業：其中T_Major是專業表，T_S ...

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

下麵是Db First的方式：

1. 資料庫庫中存在兩個表，一個是專業表，一個學生表，一個學生只能屬於一個專業：

其中T_Major是專業表，T_Student是學生表，StudentId是學號，MajorId是專業Id，T_Major與T_Student是一對多的關係。

2. 項目中添加資料庫實體模型

因為之前沒有配置過資料庫連接，所以點擊“新建庫連接”，如果之前配置過資料庫連接，可以直接從下拉列表中選擇或者新建

選擇需要生成的表/存儲過程等

點擊“完成”

這裡會彈出如下圖的視窗，然後選擇確定(如果再彈出，也選擇確定)，如果不小心點擊了取消，可以在模型設計界面Ctrl + S(保存的快捷鍵)，或如下圖的操作，然後會彈出視窗，一直確定就行。

這裡是使用MVC，所以添加一個控制器來測試（這裡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();
            }
        }
    }
}

View Code

同樣的方法添加一個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();
            }
        }
    }
}

View Code

由於學生表MajorId依賴於Major表，所以需要先有專業，才能新增學生數據(這裡不討論是否合理)

編寫邏輯代碼，創建視圖

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("參數錯誤");
            }
            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("參數錯誤");
            }
            return View(entity);
        }

        // POST: Major/Edit/5
        [HttpPost]
        public ActionResult Edit(T_Major entity)
        {
            if (entity == null)
            {
                return Content("參數錯誤");
            }
            var entities = new EFDbEntities();
            #region 方式一 
            ////該方式一般是根據主鍵先讀取數據，然後再逐個賦值，最後更新
            //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體(可能是new出來的並且對主鍵等的屬性賦值好了)附加到上下文，然後標記狀態為修改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();
            }
        }
    }
}

View Code

添加專業：

專業列表：

同樣實現學生控制器與視圖：

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("參數錯誤");
            }
            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");
        }
    }
}

View Code

添加學生時，報錯如下：

於是在控制器中增加如下代碼：

刷新頁面：

編輯：

刪除：

列表：

在MajorController中有介紹EF的兩種更新方式