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Wednesday, February 4, 2015

Using Transaction Scope in Entity Framework

Entity Framework transaction scope examples

Transactions as a core building block of entity framework. The DbContext object which we heavily use for interacting with the database uses transactions internally without you having to do anything extra. In case you need to manually provide transaction support, here is how you can do it.
In this post, I cover three cases in which transaction scope is being used to show rollback when an error occurs during an update of multiple entities:
  1. when you have multiple save calls to the context;
  2. when you have  single save with multiple object; and
  3. transactions across multiple contexts.
Let’s first review our simple model and context object. To re-create this project, use Visual Studio 2010 console project with Entity Framework 5.0 RC bits from nuget.
Our model is a simplified version of a “Product” object and it’s definition look like this:
using System;
using System.ComponentModel.DataAnnotations;
 
namespace EFTransactionsDemo.Model
{
    public class Product
    {
        public int Id { get; set; }
        [Required]
        public string Name { get; set; }
        [Required]
        public DateTime DateAdded { get; set; }
    }
}



Our context definition looks like:

using System.Data.Entity;
using System.Data.Entity.ModelConfiguration.Conventions;
 
namespace EFTransactionsDemo.Model
{
    public class EFTDbContext : DbContext
    {
        public DbSet<Product> Products { get; set; }
         
        public EFTDbContext() : 
            base("EFTransactionsDemo")
        {
            // disable proxy creation 
            this.Configuration.ProxyCreationEnabled = false;
        }
         
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            // Tell Code First to ignore PluralizingTableName convention
            // If you keep this convention then the generated tables will have pluralized names.
            modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
        }
    }
}



The main method (this is demo code; in production environments, please make sure to use proper programming paradigms, do error handling, parameter checks, etc.), calls three functions that demonstrate the use of transaction scope for the three scenarios I listed above.

using System;
using System.Linq;
using System.Transactions;
using EFTransactionsDemo.Model;

namespace EFTransactionsDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            // setup
            CreateDatabase();

            // transaction demo - 1
            // wrap multiple save calls within one transaction
            // and roll back on a bad one
            TestMultipleSaveCalls();

            // transaction demo - 2
            // wrap multiple adds and one save within one transaction
            // and roll back on a bad one
            TestMultipleAddWithOneSaveCall();

            // transaction demo - 3
            // multiple contexts in same transaction
            TestMultipleContexts();
        }

        private static void TestMultipleSaveCalls()
        {
            // good product
            Product goodProduct = new Product()
            {
                Name = "My awesome book",
                DateAdded = DateTime.UtcNow
            };

            // invalid product
            Product invalidProd = new Product()
            {
                Name = "My awesome book part 2"
                // note - no date added specified
            };

            // define our transaction scope
            var scope = new TransactionScope(
                // a new transaction will always be created
                TransactionScopeOption.RequiresNew,
                // we will allow volatile data to be read during transaction
                new TransactionOptions()
                {
                    IsolationLevel = IsolationLevel.ReadUncommitted
                }
            );

            try
            {
                // use the scope we just defined
                using (scope)
                {
                    // create a new db context
                    using (var ctx = new EFTDbContext())
                    {
                        // add the product
                        ctx.Products.Add(goodProduct);
                        // save
                        ctx.SaveChanges();

                        // add the invalid product
                        ctx.Products.Add(invalidProd);
                        // save
                        ctx.SaveChanges();
                    }

                    // everything good; complete
                    scope.Complete();
                }
            }
            catch { }

            // verify that we actually rolled back
            using (var ctx = new EFTDbContext())
            {
                Console.WriteLine(ctx.Products.Count());
            }
        }

        private static void TestMultipleAddWithOneSaveCall()
        {
            // good product
            Product goodProduct = new Product()
            {
                Name = "My awesome book",
                DateAdded = DateTime.UtcNow
            };

            // invalid product
            Product invalidProd = new Product()
            {
                Name = "My awesome book part 2"
                // note - no date added specified
            };

            // define our transaction scope
            var scope = new TransactionScope(
                // a new transaction will always be created
                TransactionScopeOption.RequiresNew,
                // we will allow volatile data to be read during transaction
                new TransactionOptions()
                {
                    IsolationLevel = IsolationLevel.ReadUncommitted
                }
            );

            try
            {
                // use the scope we just defined
                using (scope)
                {
                    // create a new db context
                    using (var ctx = new EFTDbContext())
                    {
                        // add the product
                        ctx.Products.Add(goodProduct);

                        // add the invalid product
                        ctx.Products.Add(invalidProd);
                        // save
                        ctx.SaveChanges();
                    }

                    // everything good; complete
                    scope.Complete();
                }
            }
            catch { }

            // verify that we actually rolled back
            using (var ctx = new EFTDbContext())
            {
                Console.WriteLine(ctx.Products.Count());
            }
        }

        private static void TestMultipleContexts()
        {
            // good product
            Product goodProduct = new Product()
            {
                Name = "My awesome book",
                DateAdded = DateTime.UtcNow
            };

            // invalid product
            Product invalidProd = new Product()
            {
                Name = "My awesome book part 2"
                // note - no date added specified
            };

            // define our transaction scope
            var scope = new TransactionScope(
                // a new transaction will always be created
                TransactionScopeOption.RequiresNew,
                // we will allow volatile data to be read during transaction
                new TransactionOptions()
                {
                    IsolationLevel = IsolationLevel.ReadUncommitted
                }
            );

            try
            {
                // use the scope we just defined
                using (scope)
                {
                    // create a new db context
                    var firstCtx = new EFTDbContext();
                    // create a second context
                    var secondCtx = new EFTDbContext();

                    // add the product to first context
                    firstCtx.Products.Add(goodProduct);
                    // save
                    firstCtx.SaveChanges();

                    // add the invalid product to second context
                    secondCtx.Products.Add(invalidProd);
                    // save
                    secondCtx.SaveChanges();

                    // everything good; complete
                    scope.Complete();
                }
            }
            catch { }

            // verify that we actually rolled back
            using (var ctx = new EFTDbContext())
            {
                Console.WriteLine(ctx.Products.Count());
            }
        }

        private static void CreateDatabase()
        {
            using (var ctx = new EFTDbContext())
            {
                ctx.Database.CreateIfNotExists();
            }
        }
    }
}

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