An entity object cannot be referenced by multiple instances of IEntityChangeTracker

When creating a thread to run a script I get:

"An entity object cannot be referenced by multiple instances of IEntityChangeTracker”?"

More info on fix:

http://stackoverflow.com/questions/620084/how-to-get-rid-off-an-entity-object-cannot-be-referenced-by-multiple-instances-o

(store data context in HttpContext

What thread are you creating? What should I do to reproduce the exception?

We have a script which accepts a CSV and updates all product variant stock levels. Trying to reproduce this for you.

The method which is complaining is:

/// <summary>
        /// Updates the product variant
        /// </summary>
        /// <param name="productVariantId">The product variant identifier</param>
        /// <param name="cycleLength">The cycle length</param>
        /// <param name="stockQuantity">The stock quantity</param>
        /// <param name="productCost">The product cost</param>
        /// <returns>Product variant</returns>
        public static ProductVariant UpdateProductVariant(int productVariantId, int stockQuantity, int cycleLength, decimal productCost)
        {

            var productVariant = GetProductVariantById(productVariantId);
            if (productVariant == null)
                return null;

            var context = ObjectContextHelper.CurrentObjectContext;
            if (!context.IsAttached(productVariant))
                context.ProductVariants.Attach(productVariant);


            productVariant.CycleLength = cycleLength;
            productVariant.StockQuantity = stockQuantity;
            productVariant.ProductCost = productCost;

            context.SaveChanges();

            if (ProductManager.CacheEnabled)
            {
                
            }

            return productVariant;
        }

Iits the attached method which throws an error.

I am going some further tests and will report back.

Changing the above method to:

public static ProductVariant UpdateProductVariant(int productVariantId, int stockQuantity, int cycleLength, decimal productCost)
        {
            var context = ObjectContextHelper.CurrentObjectContext;
            var productVariant = context.ProductVariants.FirstOrDefault(p => p.ProductVariantId == productVariantId);

            if (productVariant == null)
                return null;

            productVariant.CycleLength = cycleLength;
            productVariant.StockQuantity = stockQuantity;
            productVariant.ProductCost = productCost;

            context.SaveChanges();

            if (ProductManager.CacheEnabled)
            {
                
            }

            return productVariant;
        }

Worked.

I.E it was the attach method which through the error.

Could you please post source code of your ProductManager.GetProductVariantById(int productVariantId) method here?

/// <summary>
        /// Gets a product variant
        /// </summary>
        /// <param name="productVariantId">Product variant identifier</param>
        /// <returns>Product variant</returns>
        public static ProductVariant GetProductVariantById(int productVariantId)
        {
            if (productVariantId == 0)
                return null;

            string key = string.Format(PRODUCTVARIANTS_BY_ID_KEY, productVariantId);
            object obj2 = NopRequestCache.Get(key);
            if (ProductManager.CacheEnabled && (obj2 != null))
            {
                return (ProductVariant)obj2;
            }

            var context = ObjectContextHelper.CurrentObjectContext;
            var query = from pv in context.ProductVariants
                        where pv.ProductVariantId == productVariantId
                        select pv;
            var productVariant = query.SingleOrDefault();

            if (ProductManager.CacheEnabled)
            {
                NopRequestCache.Add(key, productVariant);
            }
            return productVariant;
        }

I've the same problem.
The problem is verified only when running non-webApplication that uses NopCommerce Libraries. (The ASPNetObjectContextManager cannot be used!!!)

Sorry for my bad english!

Best regards

http://dotnetslackers.com/articles/ado_net/Managing-Entity-Framework-ObjectContext-lifespan-and-scope-in-n-layered-ASP-NET-applications.aspx

this is a great example!
Hope it helps

I have the exact same issue and I am also trying to update stock levels