Optimictics Handling Concurrency Conflicts doesn't work!

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Optimictics Handling Concurrency Conflicts doesn't work!

sblb 1,231

Hi, my application is made with blazor wasm. I try to implement the optimistic Concurrency.

I follow up the tutorial from mricosoft https://learn.microsoft.com/en-us/aspnet/core/data/ef-rp/concurrency?view=aspnetcore-7.0&tabs=visual-studio

but I didn't understand clear this mechanism.

I use the Timestemp in class model. After I open two browsers page to test handling concurrency but I didn't see any error message for all fields that don't match the database values:

The classe that I use :

  public class ProjetModel 
    {
        [Key]
        public int IdProjet { get; set; }
        [Required]
        public DateTime DateProjet { get; set; }
        [Required]
        public string? Title { get; set; }        
        public string? Type { get; set; }
        public string? Level { get; set; }
        public bool? IsCompleted { get; set; }
        public string? Statut { get; set; }
        public int ProjetCount { get; set; }
        public string? ProjetCountId {
            get
            {
                return $"{ProjetCount.ToString().PadLeft(3, '0')}";
            }
            set { }
        }

        [Timestamp]
        public byte[]? ConcurrencyToken { get; set; }

        public List<ActionItemProjet>? ActionItemProjets { get; set; }
    }

I've tested two PUT method

First test

        [HttpPut]
        public async Task<IActionResult> Put(ProjetModel projet)
        { 

            _context.Entry(projet).State = EntityState.Modified;
            await _context.SaveChangesAsync();
            return NoContent();
        }

EF didn't throw an error. If I understand in this context, EF code will compare the timestamp to the one in the database and show error if no match.

Second test : it here that i tried to follow up the Microsoft tutorial

[HttpPut]
        public async Task<IActionResult> Put(ProjetModel projet)
        {
            var toUpdate = await _context.ProjetModels.FirstOrDefaultAsync(x => x.IdProjet == projet.IdProjet);

            _context.Entry(toUpdate).Property(d => d.ConcurrencyToken).OriginalValue = projet.ConcurrencyToken;

            if (await TryUpdateModelAsync<ProjetModel>(
                toUpdate,
               "Projet",
                s => s.Title, s => s.Type, s => s.Statut, s => s.DateProjet))
            {
                try
                {
                    await _context.SaveChangesAsync();
                    return RedirectToPage("./ppage");
                }
                catch (DbUpdateConcurrencyException ex)
                {
                    var exceptionEntry = ex.Entries.Single();
                    var clientValues = (ProjetModel)exceptionEntry.Entity;
                    var databaseEntry = exceptionEntry.GetDatabaseValues();
                    if (databaseEntry == null)
                    {
                        ModelState.AddModelError(string.Empty, "Unable to save. " +
                            "The line was deleted by another user.");
                        return RedirectToPage("./ppage");

                    }
                    var dbValues = (ProjetModel)databaseEntry.ToObject();
                    await SetDbErrorMessage(dbValues, clientValues);
                    // Save the current ConcurrencyToken so next postback
                    // matches unless an new concurrency issue happens.
                    projet.ConcurrencyToken = (byte[])dbValues.ConcurrencyToken;
                    ModelState.Remove($"{nameof(projet)}.{nameof(projet.ConcurrencyToken)}");
                }
                
            }
            return RedirectToPage("./ppage");
            // _context.Entry(projet).State = EntityState.Modified;
            // await _context.SaveChangesAsync();
            // return NoContent();
        }

        private async Task SetDbErrorMessage(ProjetModel dbValues,
                                         ProjetModel clientValues)
            {

                    if (dbValues.Title != clientValues.Title)
                    {
                        ModelState.AddModelError("Department.Name",
                            $"Current value: {dbValues.Title}");
                    }
                    if (dbValues.Type != clientValues.Type)
                    {
                        ModelState.AddModelError("Department.Budget",
                            $"Current value: {dbValues.Type:c}");
                    }
                    if (dbValues.DateProjet != clientValues.DateProjet)
                    {
                        ModelState.AddModelError("Department.StartDate",
                            $"Current value: {dbValues.DateProjet:d}");
                    }
                    if (dbValues.Statut != clientValues.Statut)
                    {
                        ModelState.AddModelError("Department.StartDate",
                            $"Current value: {dbValues.Statut:d}");
                    }
            ModelState.AddModelError(string.Empty,
                                       "The record you attempted to edit "
                                     + "was modified by another user after you. The "
                                     + "edit operation was canceled and the current values in the database "
                                     + "have been displayed. If you still want to edit this record, click "
                                     + "the Save button again.");
        }

In case the put method doesn't work.

I really need some help i) to understand the mechanism of optimistic and ii) help me to get the modification of put method

Thanks in advance to your help

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Answer 1

AgaveJoe 30,126

I really need some help i) to understand the mechanism of optimistic and ii) help me to get the modification of put method

It is impossible to know what you are thinking, what you know, what you don't know... What I do know from your many threads is the subject of your posts are never the actual problem. Maybe your test is faulty or some other problem.

Anyway, I wrote an example based on your code and the [Timestamp] attribute functions exactly as documented.

Model

    public class ProjetModel
    {
        [Key]
        public int ProjetId { get; set; }
        [Required]
        public DateTime DateProjet { get; set; }
        [Required]
        public string? Title { get; set; }
        public string? Type { get; set; }
        public string? Level { get; set; }
        public bool? IsCompleted { get; set; }
        public string? Statut { get; set; }
        public int ProjetCount { get; set; }
        public string? ProjetCountId
        {
            get
            {
                return $"{ProjetCount.ToString().PadLeft(3, '0')}";
            }
            set { }
        }

        [Timestamp]
        public byte[]? ConcurrencyToken { get; set; }

        public List<ActionItemProjet>? ActionItemProjets { get; set; }
    }

    public class ActionItemProjet
    {
        [Key]
        public int ActionItemProjetId { get; set; }
        public string ActionItemProjetName { get; set;}

        public int? ProjectId { get; set; }
        public ProjetModel? ProjetModel { get; set; }
    }

I let Visual Studio scaffold the controller and I modified the GET actions to Include the ActionItemProjets collection.

    [Route("api/[controller]")]
    [ApiController]
    public class ProjetModelsController : ControllerBase
    {
        private readonly ApplicationDbContext _context;

        public ProjetModelsController(ApplicationDbContext context)
        {
            _context = context;
        }

        // GET: api/ProjetModels
        [HttpGet]
        public async Task<ActionResult<IEnumerable<ProjetModel>>> GetProjetModels()
        {
          if (_context.ProjetModels == null)
          {
              return NotFound();
          }
            return await _context.ProjetModels
                .Include(a =>a.ActionItemProjets).ToListAsync();
        }

        // GET: api/ProjetModels/5
        [HttpGet("{id}")]
        public async Task<ActionResult<ProjetModel>> GetProjetModel(int id)
        {
          if (_context.ProjetModels == null)
          {
              return NotFound();
          }
            var projetModel = await _context.ProjetModels
                .Include(a => a.ActionItemProjets)
                .SingleOrDefaultAsync(p => p.ProjetId == id);

            if (projetModel == null)
            {
                return NotFound();
            }

            return projetModel;
        }

        // PUT: api/ProjetModels/5
        // To protect from overposting attacks, see https://go.microsoft.com/fwlink/?linkid=2123754
        [HttpPut("{id}")]
        public async Task<IActionResult> PutProjetModel(int id, ProjetModel projetModel)
        {
            if (id != projetModel.ProjetId)
            {
                return BadRequest();
            }

            _context.Entry(projetModel).State = EntityState.Modified;

            try
            {
                await _context.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!ProjetModelExists(id))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }

            return NoContent();
        }

        // POST: api/ProjetModels
        // To protect from overposting attacks, see https://go.microsoft.com/fwlink/?linkid=2123754
        [HttpPost]
        public async Task<ActionResult<ProjetModel>> PostProjetModel(ProjetModel projetModel)
        {
          if (_context.ProjetModels == null)
          {
              return Problem("Entity set 'ApplicationDbContext.ProjetModels'  is null.");
          }
            _context.ProjetModels.Add(projetModel);
            await _context.SaveChangesAsync();

            return CreatedAtAction("GetProjetModel", new { id = projetModel.ProjetId }, projetModel);
        }

        // DELETE: api/ProjetModels/5
        [HttpDelete("{id}")]
        public async Task<IActionResult> DeleteProjetModel(int id)
        {
            if (_context.ProjetModels == null)
            {
                return NotFound();
            }
            var projetModel = await _context.ProjetModels.FindAsync(id);
            if (projetModel == null)
            {
                return NotFound();
            }

            _context.ProjetModels.Remove(projetModel);
            await _context.SaveChangesAsync();

            return NoContent();
        }

        private bool ProjetModelExists(int id)
        {
            return (_context.ProjetModels?.Any(e => e.ProjetId == id)).GetValueOrDefault();
        }
    }

Swagger is used to test EF's optimistic concurrency . First the GET by Id action is called to get ProjetId = 1.

[
  {
    "projetId": 1,
    "dateProjet": "2023-09-15T07:37:13.8697323",
    "title": "concurrency test 1",
    "type": "Type 1",
    "level": "Level 1",
    "isCompleted": false,
    "statut": "Statut 1",
    "projetCount": 0,
    "projetCountId": "000",
    "concurrencyToken": "AAAAAAAAB9I=",
    "actionItemProjets": [
      {
        "actionItemProjetId": 1,
        "actionItemProjetName": "ActionItemProjetName 1",
        "projectId": null,
        "projetModel": null
      },
      {
        "actionItemProjetId": 2,
        "actionItemProjetName": "ActionItemProjetName 2",
        "projectId": null,
        "projetModel": null
      }
    ]
  }
]

Next, the concurrencyToken is changed to AAAAAAAAB9A= to force a concurrency exception. Finally, the payload is summitted to the PUT action. The result is an exception as expected.

Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException: The database operation was expected to affect 1 row(s), but actually affected 0 row(s); data may have been modified or deleted since entities were loaded. See http://go.microsoft.com/fwlink/?LinkId=527962 for information on understanding and handling optimistic concurrency exceptions.

Perhaps try debugging your code and paying closer attention to what you're doing and what the code is doing.

sblb 1,231

Thank you I tried it.

If I want to have the message to edit page as the Microsoft tutorial

User's image

How I can do it ? in my first post I added await SetDbErrorMessage(dbValues, clientValues);

Is it possible to implement it in your example as below :

[HttpPut("{id}")]
        public async Task<IActionResult> PutProjetModel(int id, ProjetModel projetModel)
        {
            if (id != projetModel.ProjetId)
            {
                return BadRequest();
            }

            _context.Entry(projetModel).State = EntityState.Modified;

            try
            {
                await _context.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!ProjetModelExists(id))
                {
                    return NotFound();
                }
                else
                {
                   // throw;

			var exceptionEntry = ex.Entries.Single();
			var clientValues = (ProjetModel)exceptionEntry.Entity;
			var databaseEntry = exceptionEntry.GetDatabaseValues();
			var dbValues = (ProjetModel)databaseEntry.ToObject(); 
	       await SetDbErrorMessage(dbValues, clientValues); 
           var dbValues = (ProjetModel)databaseEntry.ToObject();

			projet.ConcurrencyToken = (byte[])dbValues.ConcurrencyToken;               
		  ModelState.Remove($"{nameof(projet)}.{nameof(projet.ConcurrencyToken)}");

                }
            }

            return NoContent();
        }

AgaveJoe 30,126

If I want to have the message to edit page as the Microsoft tutorial How I can do it ? in my first post I added await SetDbErrorMessage(dbValues, clientValues); Is it possible to implement it in your example as below :

After fixing your syntax errors, I came up with the following.

        [HttpPut("{id}")]
        public async Task<IActionResult> PutProjetModel(int id, ProjetModel projetModel)
        {
            if (id != projetModel.ProjetId)
            {
                return BadRequest();
            }

            _context.Entry(projetModel).State = EntityState.Modified;

            try
            {
                await _context.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException ex)
            {
                if (!ProjetModelExists(id))
                {
                    return NotFound();
                }
                else
                {
                    //throw;

                    var exceptionEntry = ex.Entries.Single();
                    var clientValues = (ProjetModel)exceptionEntry.Entity;
                    var databaseEntry = exceptionEntry.GetDatabaseValues();
                    var dbValues = (ProjetModel)databaseEntry.ToObject();
                    await SetDbErrorMessage(dbValues, clientValues);

                    projetModel.ConcurrencyToken = (byte[])dbValues.ConcurrencyToken;
                    ModelState.Remove($"{nameof(projetModel)}.{nameof(projetModel.ConcurrencyToken)}");
                    return BadRequest(ModelState);
                }
            }

            return NoContent();
        }

Using the same testing strategy as above and changing the name field to "concurrency test 2" (it was "concurrency test 1"), the 400 response is...

{
  "": [
    "The record you attempted to edit was modified by another user after you. The edit operation was canceled and the current values in the database have been displayed. If you still want to edit this record, click the Save button again."
  ],
  "Department.Name": [
    "Current value: concurrency test 1"
  ]
}

The Blazor client should catch the the 400 response, read the contents, and update the UI accordingly. I have no way of knowing if you have written any code on the client to handle a concurrency error or any of the HTTP responses other than 2XX.

sblb 1,231

@AgaveJoe thank you to your support.

I didn't arrive to rendering the message in Razor page

<RadzenDataGridColumn TItem="ProjetModel" Property="Title" Title="Title" Width="250px">                           <EditTemplate Context="projet"> 
	<RadzenTextBox @bind-Value="projet.Title" Name="title" MaxLength="80" />
    <RadzenTextBox @bind-Value="projet.Title" Name="title" MaxLength="80" />

    <RadzenRequiredValidator Component="title" Text="Title is required" Popup="true" />                                                       </EditTemplate>                    
 </RadzenDataGridColumn> 


<RadzenButton Icon="check" ButtonStyle="ButtonStyle.Success" Variant="Variant.Flat" Size="ButtonSize.Medium" Click="@(args => SaveRow(projet))">

@code{

 ProjetModel dev = new ProjetModel();

protected override async Task OnInitializedAsync() 
 {   
  await base.OnInitializedAsync();
   projet = await client.GetFromJsonAsync<ProjetModel[]>("api/projetbe");
   }

async Task SaveRow()
{   
	await client.PutAsJsonAsync("api/projetbe", projet);             uriHelper.NavigateTo("ppage");
	projetBEToInsert = null;         
	}

}

HAve you an idea why it's not rendering in UI?

AgaveJoe 30,126 Reputation points

2023-09-18T13:29:16.9166667+00:00

HAve you an idea why it's not rendering in UI?

You did not write any code to handle the 400 response.
sblb 1,231 Reputation points

2023-09-18T14:08:17.9333333+00:00

If understand we modified the put method to receive an exception;

Then I don't know how to write code to handle the 400 response. Do you exist a middleware for tht?
AgaveJoe 30,126 Reputation points

2023-09-18T15:43:34.68+00:00

If understand we modified the put method to receive an exception;

Not exactly. You asked how to catch a concurrency exception and return a model state error similar to the Razor Page tutorial linked in your first post. Since this is a Web API question, I thought it was logical to return the concurrency error message in an HTTP 400 status response. This way you can write code that handles a 200 (Ok) and a 400 (Bad Request).

Then I don't know how to write code to handle the 400 response. Do you exist a middleware for tht?

I recommend learning the basics. See any HttpClient tutorial.

Make HTTP requests with the HttpClient class
sblb 1,231 Reputation points

2023-09-18T18:46:31.9366667+00:00
So I don't understand because I invoke the put method in razor page

async Task SaveRow() { await client.PutAsJsonAsync("api/projetbe", projet); uriHelper.NavigateTo("ppage"); projetBEToInsert = null; }

I confirm that I received 400 response

write code that handles a 200 (Ok) and a 400 (Bad Request).

Bah I don't know how I can do that!
AgaveJoe 30,126 Reputation points

2023-09-18T22:31:20.1566667+00:00

Bah I don't know how I can do that!

Write an "if" statement.

sblb 1,231

I think that I can do that

async Task SaveRow()
{   
 Using var test = await client.PutAsJsonAsync("api/projetbe", projet);

if(!test.IsSuccessStatusCode) 
{

//here I have to call thr'e message in put method to rendering in UI
return;
}

sblb 1,231

@AgaveJoe

I tried it and it doesn't work

 private string errorMessage;
      async Task OnUpdateRow(ProjetModel newRow)
        {
            using var response = await client.PutAsJsonAsync("api/projetbe", newRow);
             if(!response.IsSuccessStatusCode) 
          {         
                errorMessage = response.ReasonPhrase;
                Console.WriteLine($"There was an error! {errorMessage}");
                return;
          } 
            dev = await response.Content.ReadFromJsonAsync<ProjetModel>();
            uriHelper.NavigateTo("ppage");
            projetBEToUpdate = null;

        }

I received the message : the input does not contain any JSON tokens. Expected the input to start with a valid JSON token

I don't understand how I can rendering the message from send SetDbErrorMessage

ModelState.AddModelError(string.Empty,
                                       "The record you attempted to edit "
                                     + "was modified by another user after you. The "
                                     + "edit operation was canceled and the current values in the database "
                                     + "have been displayed. If you still want to edit this record, click "
                                     + "the Save button again.");

thanks in advance to your help

AgaveJoe 30,126 Reputation points

2023-09-19T22:17:37.3933333+00:00

I received the message : the input does not contain any JSON tokens. Expected the input to start with a valid JSON token

The error message usually means JSON was not returned. Try debugging your code. I'm pretty sure you can figure out the bug if you made even the slightest effort.

sblb 1,231

Sorry I've make an effort but it doesn't work.

Could you please give some advise? it's first time that I try to use HTTP Error Handling to rendering in UI.

I've have tested the put method and it's ok; now if I do understand I have to invoke a put method when the conflicts appear.

ProjetModel? projetBEToUpdate;
 async Task OnUpdateRow(ProjetModel newRow)
        {
            using var response = 
            await client.PutAsJsonAsync("api/projetbe", newRow);
         if(!response.IsSuccessStatusCode) 
          {         
               await client.PutAsJsonAsync("api/projetbe", newRow);
              return;
          } 
            dev = await response.Content.ReadFromJsonAsync<ProjetModel>();
            uriHelper.NavigateTo("ppage");
            projetBEToUpdate = null;

        }

AgaveJoe 30,126 Reputation points

2023-09-20T12:34:49.5166667+00:00

I've have tested the put method and it's ok; now if I do understand I have to invoke a put method when the conflicts appear.

The Put action returns a 204 (No content) or a 400 (Bad Request). There is no reason to make a duplicate request.

To be clear, there is a lot of design and coding left to do. Get to work.
sblb 1,231 Reputation points

2023-09-20T14:37:58.2+00:00

In that case, could you point me in the right direction?

Do I need to create a ProjeModelHttpRepository service?
AgaveJoe 30,126 Reputation points

2023-09-20T15:07:20.77+00:00

In that case, could you point me in the right direction?

Use the Visual Studio debugger and the browser's dev tools to learn how your code works.

Do I need to create a ProjeModelHttpRepository service?

It seems to me you are struggling with basic conditional logic; if/else. You'll need to explain how creating a repository pattern magically solves this problem.

Keep in mind, you asked two question in this post and both were answered.

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Optimictics Handling Concurrency Conflicts doesn't work!

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