Entity Framework Tutorial Basics（23）：Add Single Entity

Add New Entity using DBContext in Disconnected Scenario:

In this chapter you will learn how to add new entity in DbContext in the disconnected scenario, which in turn inserts a new row in a database table.

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 add 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 code shows how to save a single entity.

class Program
{
    static void Main(string[] args)
    {
        // create new Student entity object in disconnected scenario (out of the scope of DbContext)
        var newStudent = new Student();

        //set student name
        newStudent.StudentName = "Bill";

        //create DBContext object
        using (var dbCtx = new SchoolDBEntities())
        {
            //Add Student object into Students DBset
            dbCtx.Students.Add(newStudent);

            // call SaveChanges method to save student into database
            dbCtx.SaveChanges();
        }
    }
}

As you can see in the above code snippet, first, we have created a new Student entity object and set StudentName to 'Bill'. Second, we have created a new DBContext object and added newStudent into Students EntitySet. Third, we called SaveChanges method of DBContext which will execute the following insert query to the database.

exec sp_executesql N'INSERT [dbo].[Student]([StudentName], [StandardId])
VALUES (@0, NULL)
SELECT [StudentID], [RowVersion]
FROM [dbo].[Student]
WHERE @@ROWCOUNT > 0 AND [StudentID] = scope_identity(),@0='Bill'

Alternatively, we can also add entity into DBContext.Entry and mark it as Added which results in the same insert query:

class Program
{
    static void Main(string[] args)
    {
        // create new Student entity object in disconnected scenario (out of the scope of DbContext)
        var newStudent = new Student();

        //set student name
        newStudent.StudentName = "Bill";

        //create DBContext object
        using (var dbCtx = new SchoolDBEntities())
        {
            //Add newStudent entity into DbEntityEntry and mark EntityState to Added
            dbCtx.Entry(newStudent).State = System.Data.Entity.EntityState.Added;

            // call SaveChanges method to save new Student into database
            dbCtx.SaveChanges();
        }
    }
}

So, in this way, you can add a new single entity in the disconnected scenario.

In the next chapter, you will learn how to update an existing single entity in the disconnected scenario.