How to send a List of objects to asp.net core web api

Question

How to send a List of objects to asp.net core web api

Seth Isaacks 11

Hello

I have a asp.net core web api, that I calling from Xamarin. The normal CRUD methods work fine. I am trying however to add a method to the web api to send a list of objects. However I keep getting an error stating (see below). Ive also included my client side code and the method on the web api. I have googled and googled and googled, I cannot figure out what I am doing wrong.

My client side code looks like:
public async Task<bool> DiffSyncAsync(string jsonUpate)
{
var httpClient = new HttpClient();
HttpContent content = new StringContent(jsonUpate);
content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
var result = await httpClient.PostAsync(WebServiceURL + "DiffertialSync", content);
return result.IsSuccessStatusCode;
}

My api method looks like:
[Route("api/vehicles/DiffertialSync")]
public async Task<IActionResult> PostVehicles([FromBody] List<Vehicle> vehicles)
{
if (vehicles == null || _context.Vehicle == null)
{
return NotFound();
}

        try  
        {  
            //List<Vehicle> Vehicles = JsonConvert.DeserializeObject<List<Vehicle>>(vehiclesJson);  

            //if (Vehicles != null)  
            //{  
            //    foreach (var vehicle in Vehicles)  
            //    {  
            //        _context.Entry(vehicle).State = EntityState.Modified;  
            //        await _context.SaveChangesAsync();  
            //    }  
            //    return Ok(true);  
            //}  
               
            return Ok(false);  
             
        }  
        catch (Exception)  
        {  

            throw;  
        }  
    }

statusCode: 405, ReasonPhrase: 'Method Not Allowed', Version: 1.1, Content: System.Net.Http.StreamContent, Headers:
{
Date: Mon, 13 Jun 2022 14:00:48 GMT
Server: Microsoft-IIS/10.0
Set-Cookie: ARRAffinity=8a89f47e19228123334b19b17c93837ee63c5f8af4981359f4abaa40ce6cbea9;Path=/;HttpOnly;Secure;Domain=myautoapi20220609112603.azurewebsites.net
Set-Cookie: ARRAffinitySameSite=8a89f47e19228123334b19b17c93837ee63c5f8af4981359f4abaa40ce6cbea9;Path=/;HttpOnly;SameSite=None;Secure;Domain=myautoapi20220609112603.azurewebsites.net
X-Android-Received-Millis: 1655128849680
X-Android-Response-Source: NETWORK 405
X-Android-Selected-Protocol: http/1.1

2 answers

Your answer

Answer 1

Michael Taylor 60,161

The error is telling you that you're trying to call an endpoint and the method (POST) isn't supported on that endpoint. In your API controller action add HttpPost as an attribute.

   [HttpPost("api/vehicles/DiffertialSync")]  
   public async Task<IActionResult> PostVehicles([FromBody] List<Vehicle> vehicles)  
   {  
   }

Note also that you should be using the strongly typed ActionResult<T> return type and not IActionResult. This will help enforce compiler checking that you're returning the data you expect. It would be very bad for your API to return different types accidentally as the client won't be able to handle that.

Seth Isaacks 11 Reputation points

2022-06-13T14:34:12.197+00:00
@Michael Taylor I did, still getting the same error.
I had to do both attributes
[Route("api/vehicles/DiffertialSync")]
[HttpPost("{vehiclesJson}")]

I no longer get the error but the data is not being processed...obviously doing something wrong.

[Route("api/vehicles/DiffertialSync")]
[HttpPost("{vehiclesJson}")]
public async Task<IActionResult> PostVehicles([FromBody] string vehiclesJson)
{
if (vehiclesJson == null || _context.Vehicle == null)
{
return NotFound();
}

try { List<Vehicle> Vehicles = JsonConvert.DeserializeObject<List<Vehicle>>(vehiclesJson); if (Vehicles != null) { foreach (var vehicle in Vehicles) { _context.Entry(vehicle).State = EntityState.Modified; await _context.SaveChangesAsync(); } return Ok(true); } return Ok(false); } catch (Exception) { throw; } }

Being there is so much old/new information on the interwebs can you give me an example of your note?
My web knowledge is limited.
Michael Taylor 60,161 Reputation points

2022-06-13T14:40:44.54+00:00
That isn't correct. HttpPost accepts the URL that the endpoint will map to. Unless your endpoint is vehiclesJson then it isn't calling that endpoint. The Route attribute can also be used but you shouldn't combine endpoints using both. I'm not sure what happens. The signature I gave you is the only signature you should be using for this action. If you added anything else then it is broken.

Let's go back to your client code. You are calling the endpoint like this:

var result = await httpClient.PostAsync(WebServiceURL + "DiffertialSync", content);

For that to work with your defined endpoint WebServiceURL would need to be <baseUrl>\api\vehicles\. If it is anything else then you're calling the wrong endpoint. Try putting the fully formed URL into a temp variable and then verify that you're calling the same endpoint as defined by HttpPost.
Seth Isaacks 11 Reputation points

2022-06-13T14:47:18.097+00:00

I am confused, should the request url be <baseURL>\api\vehicles\DiffertialSync

Michael Taylor 60,161

Yes you need to send your data as JSON (or similar) format.

   //Simple structure that may or may not directly relate to DB object  
   public class Vehicle  
   {  
      public int Id { get; set; }  
      public string Name { get; set; }  
   }  
     
   //All actions use the base URL  
   ]ApiController]  
   [Route("api/vehicles")]  
   public class VehicleController : Controller  
   {  
      //URL: GET api/vehicles  
      [HttpGet]  
      public async Task<ActionResult<IEnumerable<Vehicle>>> GetVehiclesAsync ( CancellationToken cancellationToken )  
      {  
         var items = await GetVehiclesFromYourDatabaseAsync(cancellationToken).ConfigureAwait(false);  
     
         return Ok(items);  
      }  
     
      //URL: POST api/vehicles  
      [HttpPost]  
      public async Task UpdateVehicles ( [FromBody] IEnumerable<Vehicle> vehicles, CancellationToken cancellationToken )  
      {  
          foreach (var vehicle in vehicles)  
          {  
             //Get DB item - assuming you have a DbSet<Vehicle> in your EF model  
             var item = _context.Vehicles.FirstOrDefault(x => x.Id == vehicle.Id);  
             if (item != null)   
                //Update the DB object            
          };  
     
          await _context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);  
      }  
   }

Michael Taylor 60,161

Yes you need to send your data as JSON (or similar) format.

   //Simple structure that may or may not directly relate to DB object  
   public class Vehicle  
   {  
      public int Id { get; set; }  
      public string Name { get; set; }  
   }  
     
   //All actions use the base URL  
   ]ApiController]  
   [Route("api/vehicles")]  
   public class VehicleController : Controller  
   {  
      //URL: GET api/vehicles  
      [HttpGet]  
      public async Task<ActionResult<IEnumerable<Vehicle>>> GetVehiclesAsync ( CancellationToken cancellationToken )  
      {  
         var items = await GetVehiclesFromYourDatabaseAsync(cancellationToken).ConfigureAwait(false);  
     
         return Ok(items);  
      }  
     
      //URL: POST api/vehicles  
      [HttpPost]  
      public async Task UpdateVehicles ( [FromBody] IEnumerable<Vehicle> vehicles, CancellationToken cancellationToken )  
      {  
          foreach (var vehicle in vehicles)  
          {  
             //Get DB item - assuming you have a DbSet<Vehicle> in your EF model  
             var item = _context.Vehicles.FirstOrDefault(x => x.Id == vehicle.Id);  
             if (item != null)   
                //Update the DB object            
          };  
     
          await _context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);  
      }  
   }

Seth Isaacks 11 Reputation points

2022-06-13T15:05:23.553+00:00

@Michael Taylor
I am not sure what I am doing wrong.
This is my client code....where content is the SerializeObject List of objects

var result = await httpClient.PostAsync(WebServiceURL + "DiffertialSync", content);

My server method looks like this:
[HttpPost("{api/vehicles/DiffertialSync}")]
public async Task<IActionResult> PostVehicles([FromBody] List<Vehicle> vehicles)

I am confused if the server method should be a List<Vehicle> or string vehicles
I have been struggling with this for a few days.

I already have another post method that accepts one item and updates.

Michael Taylor 60,161

If you aren't already using it then add a NuGet package reference to System.Net.Http.Json to get access to the helper formatting methods.

   //To call from C#  
   public class VehiclesClient   
   {  
      //HttpClient is configured at app startup and has BaseAddress = "<baseUrl>/" which is where your API is hosted, slash on end is required  
      // e.g https://localhost:12345/  
      public VehiclesClient ( HttpClient client )  
      {  
         _client = client;  
      }  
     
      public async Task<IEnumerable<Vehicle>> GetVehiclesAsync ( CancellationToken cancellationToken )  
      {  
         return await _client.GetFromJsonAsync("api/vehicles", cancellationToken).ConfigureAwait(false);  
      }  
     
      public async Task UpdateVehiclesAsync ( IEnumerable<Vehicle> vehicles, CancellationToken cancellationToken )  
      {  
         using (var response = await _client.PostAsJsonAsync("api/vehicles", vehicles, cancellationToken).ConfigureAwait(false))  
         {  
             response.EnsureSuccessStatusCode();  
         };  
      }  
     
      private readonly HttpClient _client;  
   }

Michael Taylor 60,161 Reputation points

2022-06-13T15:12:48.987+00:00

Do not use raw JSON strings. Use the helper methods and the standard .NET objects. Refer to my example code.
Seth Isaacks 11 Reputation points

2022-06-13T15:23:32.947+00:00

@Michael Taylor I dont have 'PostAsJsonAsync' I only have Post 'PostAsync'
I am using System.net.http and that does not contain the methods you listed.
So maybe I am doing something wrong.
This is where I get so confused googling, so much information, and most of it is outdated.
Michael Taylor 60,161 Reputation points

2022-06-13T15:24:44.673+00:00

I mentioned in the post that you need to add a Nuget package reference to System.Net.Http.Json. This will bring in the extension methods to auto-add support for JSON so you don't have to write that boilerplate code yourself. Add the package reference and the methods will be available.
Seth Isaacks 11 Reputation points

2022-06-13T15:48:42.863+00:00

@Michael Taylor Yeah its still not working, I followed your example. I already have a post method, that method stopped working.
So I commented out the Post method I added for the list and the post method started wroking.
I noticed in your example you didnt have a dfferent route for the post method.
So If I have two post methods what do I do? I thought adding this would work baseUrl/api/vehicles/DiffertialSync would work...but its not working

So this is my single post method
[HttpPost]
public async Task<ActionResult<Vehicle>> PostVehicle(Vehicle vehicle)

This is the one to update a LIST
[HttpPost("{api/vehicles/DiffertialSync}")]
public async Task<IActionResult> PostVehicles([FromBody] IENumberable<Vehicle> vehicles)

If I have both of these, the first one does not work...how can I have both?

Michael Taylor 60,161

You cannot have 2 post methods with the same URL. In my sample I had a single post method so there was no reason to add a complicated URL. To support 2 different post methods you would just have different URLs.

   //All actions use the base URL  
   ]ApiController]  
   [Route("api/vehicles")]  
   public class VehicleController : Controller  
   {  
      //URL: GET api/vehicles  
      [HttpGet]  
      public async Task<ActionResult<IEnumerable<Vehicle>>> GetVehiclesAsync ( CancellationToken cancellationToken )  
      {  
         var items = await GetVehiclesFromYourDatabaseAsync(cancellationToken).ConfigureAwait(false);  
         return Ok(items);  
      }  
     
      [HttpPost]  
      public async Task<ActionResult<Vehicle>> PostAsync ( [FromBody] Vehicle item ) { ... }  
     
      [HttpPost("DifferentialSync")]  
      public async Task UpdateVehicles ( [FromBody] IEnumerable<Vehicle> vehicles, CancellationToken cancellationToken )  
      {  
          foreach (var vehicle in vehicles)  
          {  
             //Get DB item - assuming you have a DbSet<Vehicle> in your EF model  
             var item = _context.Vehicles.FirstOrDefault(x => x.Id == vehicle.Id);  
             if (item != null)   
                //Update the DB object            
          };  
          await _context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);  
      }

Michael Taylor 60,161 Reputation points

2022-06-13T16:00:03.957+00:00

To update a single vehicle use the POST <baseUrl>/api/vehicles endpoint. To update a list use POST <baseUrl>/api/vehicles/differentialsync
Seth Isaacks 11 Reputation points

2022-06-13T16:05:51.713+00:00

@Michael Taylor Is that not what I posted below and what I posted above that you responded too? I have two diff routes dont I??? If so then I am confused.
BTW thank you for your help...I have been struggling with this for days.

[HttpPost]
public async Task<ActionResult<Vehicle>> PostVehicle(Vehicle vehicle)

This is the one to update a LIST
[HttpPost("{api/vehicles/DiffertialSync}")]
public async Task<IActionResult> PostVehicles([FromBody] IENumberable<Vehicle> vehicles)

UPDATE: So I figured out what I did wrong, in the httpost all I need is this: [HttpPost("{DiffertialSync}")] not [HttpPost("{api/vehicles/DiffertialSync}")]
Also, maybe you forgot in your example but DiffertialSync is required to be inside curly brackets and quotation marks.

Thank yo for your assistance...finally got this figured out. I truly appreciate it
Michael Taylor 60,161 Reputation points

2022-06-13T16:40:55.007+00:00

No you don't use curly braces in the string. Curly braces are used to inject parameters from the action into the url. [HttpGet("vehicles/{id}")] would map to public Vehicle Get ( int id ). In your case you aren't passing any data as part of the URL so there are no curly braces. Data in the body are not part of the URL template.

Yes, as I mentioned earlier, the controller Route defines the base URL of all the actions (relative to the server). The Http... attributes are relative to the controller's route and eliminates the need to replicate the same prefix on every action.

Glad to hear you figured things out.

Answer 2

Seth Isaacks 11

@Michael Taylor okay well it will not work if I remove the curly braces......so what am I doing wrong then.....

Michael Taylor 60,161 Reputation points

2022-06-13T16:43:50.33+00:00

Again, given the controller with the base URL, then the attribute should just be [HttpPost("DifferetialAsync")]. Honestly though maybe you should just simplify it down to simply list.
Seth Isaacks 11 Reputation points

2022-06-13T17:04:31.843+00:00

@Michael Taylor I am not sure what you mean by "Honestly though maybe you should just simplify it down to simply list."
What do you mean by "it"?

If I do not have the curly braces it does not work. I get the Method Not Allowed.
I literally copied and pasted what you sent me.
Seth Isaacks 11 Reputation points

2022-06-13T17:39:45.007+00:00

I figured out the issue....I was using POST when I should have been Using PUT.
The list is items being updated not inserted as new items.

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How to send a List of objects to asp.net core web api

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