Lerning Entity Framework 6 ------ Handling concurrency With SQL Server Database

---

The default Way to handle concurrency of Entity Framework is using optimistic concurrency. When two clinets update the same entity, one of theirs data will be lost without any notify.

Some times, the client want to know if his data has been saved successful, so, we have to do some Extra work：

• Create a project named ConcurrencyTest

• Add a entity:

    public class Person
    {
        public int PersonId { get; set; }
  
        public string Name { get; set; }
  
        public byte[] RowVersion { get; set; }
    }
  

Please take attention to the RowVersion property. It used to record the version of the data row in a table.

Add fluent API codes:

    public class PersonMap : EntityTypeConfiguration<Person>
    {
        public PersonMap()
        {
            Property(p => p.RowVersion)
                .IsFixedLength()
                .HasMaxLength(8)
                .HasDatabaseGeneratedOption(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Computed)
                .IsRowVersion();
        }
    }

• Add a DbContext:

    public class MyContext:DbContext
    {
        public DbSet<Person> People { get; set; }
  
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Configurations.Add(new PersonMap());
        }
    }
  

• Add some test codes:

    static void Main(string[] args)
    {
        AddPerson();
        DoConcurrentcyTest();
  
        Console.Read();
    }
  
    static void DoConcurrentcyTest()
    {
        using (MyContext db1 = new MyContext())
        {
            Person p1 = db1.People.Find(1);
  
            using (MyContext db2 = new MyContext())
            {
                Person p2 = db2.People.Find(1);
                p2.Name = "Ross";
                db2.SaveChanges();
            }
  
            p1.Name = "Monnica";
            try
            {
                db1.SaveChanges();
            }
            catch (DbUpdateConcurrencyException)
            {
                Console.WriteLine("please refresh it");
            }
        }
    }
  

When you save the person entity, if someone have changed it after you get, a DbUpdateConcurrencyException will be trowed.

That's all.