Why does my web application hang up on "await _context.SaveChangesAsync();"

Question

User-1849651236 posted

Hello,

I have an Asp.Net Core 2.1, MVC, C# Web application in Visual Studio 2017 15.7.5.  My Nuget packages show that I am using Microsoft.EntityFrameworkCore.Tools 2.1.1.

In my coding shown at the end of this post, my program hangs up on this statement:

await _context.SaveChangesAsync();

and never returns control to the next statement.  I used the Visual Studio debugger to stop on the statement after that one and waited ten minutes.  It never gave control back.

I also tried it this way and got the same results:

_context.AddRange(productsRootObject.Products);
_context.SaveChanges();

Does anyone know how to debug this issue?  Is there some log that I can look at?

Thanks,
Tony

Here is my code:

    public class ProductListViewComponent : ViewComponent
    {
          private readonly ChinavasionAPIContext _context;
          private readonly IHubContext<ChvHub> _hubContext;

          public ProductListViewComponent(IHubContext<ChvHub> hubcontext, ChinavasionAPIContext context)
          {
               _context = context;
               _hubContext = hubcontext;
          }

          #region snippet1
          public async Task<IViewComponentResult> InvokeAsync()
          {
               //string MyView = "Default";
               var items = await GetItemsAsync();
               await this._hubContext.Clients.All.SendAsync("ReceiveMessage", "", "===============================================  Ready to Display Lakeside and Chinavasion Products  ===============================================");

               return View(items);
          }

          public async Task<List<ProductViewModel>> GetItemsAsync()
          {
               var model = new AccessModel();
               model.UserAccessModel = _context.UserAccessModels.Single(a => a.ID == 1);

               var accessToken = (model.UserAccessModel.AccessToken ?? TempData["accessToken"]).ToString();
               var serverUrl = (model.UserAccessModel.ServerUrl ?? TempData["serverUrl"]).ToString();
               var nopApiClient = new ApiClient(accessToken, serverUrl);
               MultipleProductModel multipleProductModel = new MultipleProductModel();
               List<Category> categories = new List<Category>();

               string jsonUrl = $"/api/products/count";
               object productsCount = nopApiClient.Get(jsonUrl);
               var nopProductsCount = JsonConvert.DeserializeObject<ProductsCount>(productsCount.ToString());
               int sinceID = 0;
               int productCount = 0;
               await this._hubContext.Clients.All.SendAsync("ReceiveMessage", "", "=============================================  Starting Lakeside Product Retrieval from Live Database  ==============================================");

               do
               {
                    productCount += 1;
                    await this._hubContext.Clients.All.SendAsync("ReceiveMessage", productCount.ToString(), " Downloading Lakeside products");
                    jsonUrl = $"/api/products?limit=250&since_id=" + sinceID.ToString() + $"&fields=id,sku,name,images,categories";
                    object productsData = nopApiClient.Get(jsonUrl);

                    var productsRootObject = JsonConvert.DeserializeObject<ProductsRootObject>(productsData.ToString());
                    multipleProductModel.MProductsApi.AddRange(productsRootObject.Products);
                    await _context.AddRangeAsync(productsRootObject.Products);
                    await _context.SaveChangesAsync();

                    var last = multipleProductModel.MProductsApi.LastOrDefault();
                    sinceID = Convert.ToInt16(last.Id);
               } while (multipleProductModel.MProductsApi.Count < nopProductsCount.Count);
}

using System.Collections.Generic;
using Newtonsoft.Json;

namespace ChinavasionAPI.DTOs
{
    public class ProductsRootObject
    {
        [JsonProperty("products")]
        public List<ProductApi> Products { get; set; }
    }
}

using Newtonsoft.Json;
using System.Collections.Generic;

{
     public class ProductApi
     {
          [JsonProperty("id")]
          public string Id { get; set; }
          [JsonProperty("sku")]
          public string Sku { get; set; }
          [JsonProperty("name")]
          public string Name { get; set; }
          [JsonProperty("images")]
          public List<Image> Images { get; set; }
          [JsonProperty("categories")]
          public string Categories { get; set; }
     }

     public class Image
     {
          [JsonProperty("id")]
          public int Id { get; set; }
          [JsonProperty("position")]
          public int Position { get; set; }
          [JsonProperty("src")]
          public string Src { get; set; }
          [JsonProperty("attachment")]
          public string Attachment { get; set; }
     }
}

using System.Collections.Generic;
using ChinavasionAPI.DTOs;

namespace ChinavasionAPI.Models.CAPIViewModels
{
     public class MultipleProductModel
     {
          public List<ProductApi> MProductsApi { get; set; }
          public List<Product> MProducts { get; set; }
          public MultipleProductModel()
          {
               this.MProductsApi = new List<ProductApi>();
               this.MProducts = new List<Product>();
          }
     }
}

Answer 1

User1881638666 posted

Hi TGirgenti,

If there is blocking call inside asynchronous call / path, it could cause deadlock if the both the threads waiting for each other to complete (SynchronizationContext).

This is what happened in your asp.net mvc application.

There is a blocking (sync) call in your method, 

object productsData = nopApiClient.Get(jsonUrl);

Fix this, by calling the asynchronous version of the method if available. eg: await nopApiClient.GetAsync(jsonUrl) ;

Note : Fix the both two places where you called blocking Get method inside the method.

Further go through the followings,

https://msdn.microsoft.com/en-us/magazine/jj991977.aspx

https://gist.github.com/jonlabelle/841146854b23b305b50fa5542f84b20c

Thanks,

Wenushka

Answer 2

User-1849651236 posted

Hello Wenushka.

Thanks for your help with this issue.

There is one thing that I am confused about.  If the blocking call is causing the problem when it gets to this:

await _context.SaveChangesAsync();

why does it not hangup on the await prior to that one?

await _context.AddRangeAsync(productsRootObject.Products);

I will read the information you pointed out and I will try to make the blocking Get you pointed out to an await

Thanks,
Tony

Answer 3

User-1849651236 posted

Hello Wenushka.

I tried your idea of making the calling of the asynchronous version of the methods and it did not work.

I changed all of my methods to public async Task and it still hangs up on "await _context.SaveChangesAsync();"

Does anyone have any idea of how to fix this problem?

Thanks,
Tony

Answer 4

User1881638666 posted

Hi TGirgenti,

Could you share the implementation of the ,

ChinavasionAPIContext context

or two methods of that class,

await _context.AddRangeAsync(productsRootObject.Products);
await _context.SaveChangesAsync();

Thanks,

Wenushka

Answer 5

User-1849651236 posted

Wenushka,

Here is my context file:

using ChinavasionAPI.Models;
using Microsoft.EntityFrameworkCore;

namespace ChinavasionAPI.Data
{
    public class ChinavasionAPIContext : DbContext
    {
        public ChinavasionAPIContext (DbContextOptions<ChinavasionAPIContext> options) : base(options)
        {
        }

          public DbSet<ChinavasionAPI.Models.QueryCall> QueryCalls { get; set; }
          public DbSet<ChinavasionAPI.Models.Setup> Setups { get; set; }
          public DbSet<ChinavasionAPI.Models.QueryAssignment> QueryAssignments { get; set; }
          public DbSet<ChinavasionAPI.Models.UserAccessModel> UserAccessModels { get; set; }
          public DbSet<ChinavasionAPI.DTOs.ProductApi> ProductApis { get; set; }
          public DbSet<ChinavasionAPI.DTOs.Image> Images { get; set; }

          protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
             modelBuilder.Entity<QueryCall>().ToTable("QueryCall");
             modelBuilder.Entity<Setup>().ToTable("Setup");
             modelBuilder.Entity<UserAccessModel>().ToTable("UserAccessModel");
             modelBuilder.Entity<QueryAssignment>().ToTable("QueryAssignment");
             modelBuilder.Entity<QueryAssignment>()
                    .HasKey(q => new { q.QueryID, q.SetupID });
        }
     }
}

Thanks for your help.

Tony

Answer 6

User1881638666 posted

hi TGirgenti,

Change how the entities is added before committing the changes to db.

Change, 

await _context.AddRangeAsync(productsRootObject.Products);

with, 

_context.ProductApis.AddRange(productsRootObject.Products);

Note: In adding the entities, you don't have to call async version of DbContext unless we have special requirement mentioned here.

https://docs.microsoft.com/en-us/ef/core/api/microsoft.entityframeworkcore.dbcontext

https://docs.microsoft.com/en-us/ef/core/api/microsoft.entityframeworkcore.dbset-1

Finally, commit the changes as usual with the,

await _context.SaveChangesAsync();

 

Answer 7

User-1849651236 posted

Wenushka,

Your suggested change did not work.

I put in a try/catch on the code where it was hanging up.  I saw this error:

An error occurred while updating the entries. See the inner exception for details.
Cannot insert explicit value for identity column in table 'ProductApis' when IDENTITY_INSERT is set to OFF.

After Googling that error, I found articles that suggested putting this annotation:

[DatabaseGenerated(DatabaseGeneratedOption.None)]

on the Id properties for the ProductApi and Image models.

That allowed me to run the program without getting the hangup and it populated the tables.

I very much appreciate your help in trying to fix this issue.

Thanks,
Tony