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

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  TGirgenti

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

  Aug 03, 2018 12:30 PM|TGirgenti|LINK

  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>();
            }
       }
  }
  

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• • Reply
  Wenushka

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

  Aug 05, 2018 05:42 AM|Wenushka|LINK

  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

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  TGirgenti

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

  Aug 05, 2018 04:55 PM|TGirgenti|LINK

  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

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• • Reply
  TGirgenti

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  345 Posts

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

  Aug 07, 2018 02:33 AM|TGirgenti|LINK

  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

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• • Reply
  Wenushka

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

  Aug 07, 2018 05:05 AM|Wenushka|LINK

  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

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  TGirgenti

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  345 Posts

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

  Aug 07, 2018 12:59 PM|TGirgenti|LINK

  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

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• • Reply
  Wenushka

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

  Aug 08, 2018 09:02 AM|Wenushka|LINK

  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();

  
   

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  TGirgenti

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

  Aug 09, 2018 02:11 PM|TGirgenti|LINK

  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

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