Entity Framework Tutorial Basics(24):Update Single Entity
2016-07-07 10:21 追忆似水流年 阅读(148) 评论(0) 编辑 收藏 举报Update Existing Entity using DBContext in Disconnected Scenario:
In this chapter, you will learn how to update a single entity in a disconnected scenario.
If you use Database-First approach, then create an Entity Data Model as shown in the previous chapter for SchoolDB sample database. Or, if you use Code-First or Model-First approach, then create entities and context classes. In any case, entities and context classes will look similar.
Here, we will see how to update a single Student entity (not entity graph). The following is a Student entity.
using System; using System.Collections.Generic; public partial class Student { public Student() { this.Courses = new HashSet<Course>(); } public int StudentID { get; set; } public string StudentName { get; set; } public Nullable<int> StandardId { get; set; } public byte[] RowVersion { get; set; } public virtual Standard Standard { get; set; } public virtual StudentAddress StudentAddress { get; set; } public virtual ICollection<Course> Courses { get; set; } }
The following is a context class.
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) { } 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; } }
The following example shows how to update a Student entity in the disconnected scenario:
Student stud; //1. Get student from DB using (var ctx = new SchoolDBEntities()) { stud = ctx.Students.Where(s => s.StudentName == "New Student1").FirstOrDefault<Student>(); } //2. change student name in disconnected mode (out of ctx scope) if (stud != null) { stud.StudentName = "Updated Student1"; } //save modified entity using new Context using (var dbCtx = new SchoolDBEntities()) { //3. Mark entity as modified dbCtx.Entry(stud).State = System.Data.Entity.EntityState.Modified; //4. call SaveChanges dbCtx.SaveChanges(); }
As you see in the above code snippet, we are doing the following steps:
- Get the existing student from DB.
- Change the student name out of Context scope (disconnected mode)
- Pass the modified entity into the Entry method to get its DBEntityEntry object and then mark its state as Modified
- Call SaveChanges() method to update student information into the database.
SaveChanges will send the following update query to the database:
exec sp_executesql N'update [dbo].[Student] set [StudentName] = @0, [StandardId] = @1 where ([StudentID] = @2)',N'@0 varchar(50), @1 int,@2 int',@0='Updated Student1',@1=299,@2=267
In this way, we can easily update a single entity using DBContext in the disconnected mode.
DbContext.Entry method returns an instance of DBEntityEntry for a specified Entity. An instance of DbEntityEntry class providea access to information about a given entity and its state. You can change the state of an entity to Added, Updated, or Deleted.
In the next chapter you will learn how to delete a single entity in the disconnected mode.