EntityFramework 學習 一 DbContext

上一節中EDM自動生成SchoolEntities類，該類繼承DbContext

EntityFramework4.1之前的版本，EDM生成的類繼承ObjectContext，使用ObjectContext稍微有點棘手，DbContext概念上與ObjectContext相似，它是ObjectContext的封裝，DbContext是EF重要的組成部分，它是領域或實體類和數據庫的橋梁

 

DbContext是主要的類負責數據和對象互相轉化

EntitySet:  DbContext包含實體集合（DBSet<TEntity>），所有與數據庫表對應的實體

Querying: DbContext將LINQ-to-Entity查詢語言轉化成SQL查詢語言，並發送給數據庫

Change Tracking: 當對象已經從數據庫中查詢到后，DbContext跟蹤實體的變化情況

Persisting Data: DbContext執行插入、更新、刪除操作

Caching: DbContext默認使用一級緩存，在一個context對象周期內，它緩存所有已經被查詢的實體

Manage Relationship: DbContext管理對象間的關系

namespace EFTutorials
{
    using System;
    using System.Data.Entity;
    using System.Data.Entity.Infrastructure;
    using System.Data.Entity.Core.Objects;
    using System.Linq;
    
    public partial class SchoolDBEntities : DbContext
    {
        public SchoolDBEntities()
            : base("name=SchoolDBEntities")
        {
        }
    
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            throw new UnintentionalCodeFirstException();
        }
    
        public virtual DbSet<Course> Courses { get; set; }
        public virtual DbSet<Standard> Standards { get; set; }
        public virtual DbSet<Student> Students { get; set; }
        public virtual DbSet<StudentAddress> StudentAddresses { get; set; }
        public virtual DbSet<Teacher> Teachers { get; set; }
        public virtual DbSet<View_StudentCourse> View_StudentCourse { get; set; }
    
        public virtual ObjectResult<GetCoursesByStudentId_Result> GetCoursesByStudentId(Nullable<int> studentId)
        {
            var studentIdParameter = studentId.HasValue ?
                new ObjectParameter("StudentId", studentId) :
                new ObjectParameter("StudentId", typeof(int));
    
            return ((IObjectContextAdapter)this).ObjectContext.ExecuteFunction<GetCoursesByStudentId_Result>("GetCoursesByStudentId", studentIdParameter);
        }
    
        public virtual int sp_DeleteStudent(Nullable<int> studentId)
        {
            var studentIdParameter = studentId.HasValue ?
                new ObjectParameter("StudentId", studentId) :
                new ObjectParameter("StudentId", typeof(int));
    
            return ((IObjectContextAdapter)this).ObjectContext.ExecuteFunction("sp_DeleteStudent", studentIdParameter);
        }
    
        public virtual ObjectResult<Nullable<decimal>> sp_InsertStudentInfo(Nullable<int> standardId, string studentName)
        {
            var standardIdParameter = standardId.HasValue ?
                new ObjectParameter("StandardId", standardId) :
                new ("StandardId", typeof(int));
    
            var studentNameParameter = studentName != null ?
                new ObjectParameter("StudentName", studentName) :
                new ObjectParameter("StudentName", typeof(string));
    
            return ((IObjectContextAdapter)this).ObjectContext.ExecuteFunction<Nullable<decimal>>("sp_InsertStudentInfo", standardIdParameter, studentNameParameter);
        }
    
        public virtual int sp_UpdateStudent(Nullable<int> studentId, Nullable<int> standardId, string studentName)
        {
            var studentIdParameter = studentId.HasValue ?
                new ObjectParameter("StudentId", studentId) :
                new ObjectParameter("StudentId", typeof(int));
    
            var standardIdParameter = standardId.HasValue ?
                new ObjectParameter("StandardId", standardId) :
                new ObjectParameter("StandardId", typeof(int));
    
            var studentNameParameter = studentName != null ?
                new ObjectParameter("StudentName", studentName) :
                new ObjectParameter("StudentName", typeof(string));
    
            return ((IObjectContextAdapter)this).ObjectContext.ExecuteFunction("sp_UpdateStudent", studentIdParameter, standardIdParameter, studentNameParameter);
        }
    }
}     

 

DbContext實例化，用來執行GRUD操作

using (var ctx = new SchoolDBEntities())
{
        
    //Can perform CRUD operation using ctx here..
}

 

從DbContext中獲取ObjectContext

DbContext API比ObjectContext用起來簡單些，然而，你可以從DbContext中得到ObjectContext的引用，

 

using (var ctx = new SchoolDBEntities())
{
    var objectContext = (ctx as System.Data.Entity.Infrastructure.IObjectContextAdapter).ObjectContext;
        
    //use objectContext here..
}