Entity Framework Code First Concurrency Control - entity-framework-4.3

Question

There
I’m using the EF code first to persist the data by following the sequence: filter => remove => add, run the attached sample(two threads run conrrrently), sometime I noticed there was no existing record return after the filtering, sometime there are two records after the filtering, what I thought/expected is - every time the filter should have one existing record return. Also, there are some exceptions raised up during saving the change.
As I known, EF by default uses the Read Committed isolation level to execute the transaction, I think that means during the filtering, the shared lock is put on the resource, but why I can observe that there is not existing record or two existing records after the filtering, the remove and add operation together should be an atomic operation, right? If I’m right, there should be only and just one record after filtering.
Is there anything I missed? How to handle this case correctly?
Please help.
Another question:
Use the LastUpdated column as the concurrency token, how to the following case correctly:
1. If the entity in the database is newer than the entity in the context, start another thread to archive the entity to the history database.
2. If the entity in the database is old than the entity in the context, retry the saving to overwrite the entity in the database.
Am i right to use the code below to handle the case:
internal void SaveChangesEx()
{
bool saveFailed;
do
{
saveFailed = false;
try
{
base.SaveChanges();
}
catch (DbUpdateConcurrencyException ex)
{
saveFailed = false;
ex.Entries.ToList().ForEach(entry =>
{
if (entry.State == System.Data.EntityState.Deleted)
{
var current = base.Set<Customer>().FirstOrDefault();
Customer rfqInDb = (Customer)entry.GetDatabaseValues();
// If the newer one aready exists, start the archive, otherwise, retry by reloading the entity from DB and marking the state as deleted
if (current.LastUpdated < customerInDb.LastUpdated)
{
using (var archiver = new CustomerArchiveDBContext())
{
archiver.RFQS.Add(current);
archiver.SaveChangesEx();
}
saveFailed = false;
}
else
{
//Refresh the context and retry
entry.Reload();
entry.State = System.Data.EntityState.Deleted;
}
}
});
}
} while (saveFailed);
}
Script: ========
CREATE TABLE [dbo].[Customers](
[FirstName] [nvarchar](20) NOT NULL,
[LastName] [nvarchar](60) NULL,
[Company] [nvarchar](250) NULL,
[Telephone] [nvarchar](20) NULL,
[LastUpdated] [datetime] NULL
) ON [PRIMARY]
Code ========
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Transactions;
using System.Data.Entity.Validation;
using System.Threading.Tasks;
using System.Threading;
using System.Data.Entity.ModelConfiguration;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration.Conventions;
namespace EFOptimisticConcurrency
{
public abstract class Entity
{
public int Id { get; set; }
}
public class Customer
: Entity
{
public string FirstName { get; set; }
/// <summary>
/// Get or set the surname of this customer
/// </summary>
public string LastName { get; set; }
/// <summary>
/// Get or set the telephone
/// </summary>
public string Telephone { get; set; }
/// <summary>
/// Get or set the company name
/// </summary>
public string Company { get; set; }
public DateTime LastUpdated { get; set; }
}
class CustomerEntityConfiguration
: EntityTypeConfiguration<Customer>
{
/// <summary>
/// Create a new instance of customer entity configuration
/// </summary>
public CustomerEntityConfiguration()
{
//configure keys and properties
this.HasKey(c => c.FirstName);
this.Ignore(c => c.Id);
this.Property(c => c.FirstName)
.HasMaxLength(20)
.IsRequired();
this.Property(c => c.LastName)
.HasMaxLength(60)
.IsRequired();
this.Property(c => c.Company)
.HasMaxLength(250);
//this.Property(c => c.LastUpdated).IsConcurrencyToken();
this.Property(c => c.Telephone)
.HasMaxLength(20);
this.ToTable("Customers");
}
}
public class CustomerContext : DbContext
{
public DbSet<Customer> Customers { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
modelBuilder.Configurations.Add(new CustomerEntityConfiguration()); ;
}
}
public class Program
{
public static volatile int showStopper = 0;
static void Main(string[] args)
{
var color = Console.ForegroundColor;
EntityFrameworkProfiler.Initialize();
Task.Factory.StartNew(() =>
{
while (true)
{
Customer customer = new Customer();
customer.FirstName = "FirstName";
customer.LastName = "Last " + new Random().Next(0, 10000).ToString();
customer.Telephone = "686868";
customer.Company = "MyCity";
customer.LastUpdated = DateTime.Now;
if (showStopper == 2)
{
Console.ReadLine();
showStopper = 0;
}
try
{
Console.WriteLine("Start the Store => " + customer.LastName + " , " + customer.LastUpdated.ToString());
{
int i = 0;
using (var customerConext = new CustomerContext())
{
Console.WriteLine("Start the filter 1 => " + customer.Telephone + " , " + customer.LastUpdated.ToString());
var matched = customerConext.Customers.Where(c => c.Telephone == "686868" && c.LastUpdated < customer.LastUpdated);
foreach (var hit in matched)
{
i++;
customerConext.Customers.Remove(hit);
}
if (i == 2)
{
Console.WriteLine("1 - 2 exist, has the problem now");
showStopper = 2;
}
else if (i == 0)
{
Console.WriteLine("1 - 0 exist, has the problem now");
showStopper = 2;
}
Console.WriteLine("Start Adding 1 => " + customer.LastName + " , " + customer.LastUpdated.ToString());
try
{
customerConext.Customers.Add(customer);
customerConext.SaveChanges();
Console.WriteLine("SaveChanges 1 => " + customer.LastName + " , " + customer.LastUpdated.ToString());
}
catch (Exception ex)
{
Console.WriteLine("Exception 1 : " + ex.Message + " => " + customer.LastName + " , " + customer.LastUpdated);
if (ex.InnerException != null)
{
Console.WriteLine("Inner Exception 2 : " + ex.InnerException.Message + " => " + customer.LastName + " , " + customer.LastUpdated);
}
}
}
}
}
catch (Exception ex)
{
Console.WriteLine("Exception 1 " + ex.Message);
if (ex.InnerException != null)
{
Console.WriteLine(ex.InnerException.Message);
}
showStopper = 2;
}
}
});
Thread.Sleep(10000);
Task.Factory.StartNew(() =>
{
while (true)
{
Console.ForegroundColor = color;
try
{
Customer customer = new Customer();
customer.FirstName = "FirstName";
customer.LastName = "Last " + new Random().Next(0, 10000).ToString();
customer.Telephone = "686868";
customer.Company = "MyCity2";
customer.LastUpdated = DateTime.Now;
if (showStopper == 3)
{
Console.ReadLine();
showStopper = 0;
}
Console.WriteLine("Start the store 2 => " + customer.LastName + " , " + customer.LastUpdated.ToString());
{
int i = 0;
using (var customerConext = new CustomerContext())
{
Console.WriteLine("Start the filter 2 => " + customer.Telephone + " , " + customer.LastUpdated.ToString());
var matched = customerConext.Customers.Where(c => c.Telephone == "686868" && c.LastUpdated < customer.LastUpdated);
foreach (var hit in matched)
{
i++;
customerConext.Customers.Remove(hit);
}
Console.WriteLine("Start Adding 2 => " + customer.LastName + " , " + customer.LastUpdated.ToString());
try
{
customerConext.Customers.Add(customer);
customerConext.SaveChanges();
Console.WriteLine("SaveChanges 2 => " + customer.LastName + " , " + customer.LastUpdated.ToString());
}
catch (Exception ex)
{
Console.WriteLine("Exception 2 : " + ex.Message + " => " + customer.LastName + " , " + customer.LastUpdated);
if (ex.InnerException != null)
{
Console.WriteLine("Inner Exception 2 : " + ex.InnerException.Message + " => " + customer.LastName + " , " + customer.LastUpdated);
}
showStopper = 2;
}
}
if (i == 2)
{
Console.WriteLine("1 - 2 exist, has the problem now");
showStopper = 2;
}
else if (i == 0)
{
Console.WriteLine("1 - 0 exist, has the problem now");
showStopper = 2;
}
}
}
catch (Exception ex)
{
Console.WriteLine("Exception 2 " + ex.Message);
if (ex.InnerException != null)
{
Console.WriteLine(ex.InnerException.Message);
}
}
}
});
Console.WriteLine("PRESS ANY KEY TO END");
Console.ReadLine();
}
}
}