Receiving multipart form-data json parameter null

Question

I am trying to receive a multipart request from Postman containg 3 parameters:

An int
A file
A Json

I receive in the controller both the file and the integer fine, but the json has all the fields as null. What could be wrong ?

Json

    [Serializable]
    public class ProcessingRecipe
    {
        [JsonPropertyName("fileId")]
        public string FileID { get; set; }
        [JsonPropertyName("srcLang")]
        public string SrcLang { get; set; }

    }

Controller

    [HttpPost]
    [Route(Routes.Routes.File.PROCESS)]
    public async Task<ActionResult<FileProcessResponse>> ProcessFileAsync([FromForm]IFormFile uploadFile,[FromForm] ProcessingRecipe recipe,[FromForm]int aa)
    {
             //the file is ok
            // the int is 33
    }

Postman

Update !!!!!

I have used according to this post to no avail:

Custom Binder

public class JsonModelBinder : IModelBinder {
    public Task BindModelAsync(ModelBindingContext bindingContext) {
        if (bindingContext == null) {
            throw new ArgumentNullException(nameof(bindingContext));
        }

        // Check the value sent in
        var valueProviderResult = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        if (valueProviderResult != ValueProviderResult.None) {
            bindingContext.ModelState.SetModelValue(bindingContext.ModelName, valueProviderResult);

            // Attempt to convert the input value
            var valueAsString = valueProviderResult.FirstValue;
            var result = Newtonsoft.Json.JsonConvert.DeserializeObject(valueAsString, bindingContext.ModelType);
            if (result != null) {
                bindingContext.Result = ModelBindingResult.Success(result);
                return Task.CompletedTask;
            }
        }

        return Task.CompletedTask;
    }
}

Controller action

public async Task<ActionResult<FileProcessResponse>> ProcessFileAsync([FromForm]IFormFile uploadFile,[ModelBinder(typeof(JsonModelBinder))] ProcessingRecipe recipe)
        {
                 //the file is ok
                // the int is 33
        }

Possible duplicate of [Upload files and JSON in ASP.NET Core Web API](https://stackoverflow.com/questions/41367602/upload-files-and-json-in-asp-net-core-web-api) — Roman Marusyk, Nov 25 '19 at 14:44
It doesn't matter here, you can use System.Text.Json but you need to create a custom ModelBinder — Roman Marusyk, Nov 25 '19 at 14:56
I have used the Custom ModelBinder to no avail.Now i get all the object as `null`. — Bercovici Adrian, Nov 25 '19 at 19:16
Possible duplicate of [how to upload a file and json data in postman](https://stackoverflow.com/questions/39037049/how-to-upload-a-file-and-json-data-in-postman) — Shivam Puri, Nov 25 '19 at 20:03
I have tried the "duplicate" solutions and they don't work for me... — Bercovici Adrian, Nov 25 '19 at 20:05
I tested your updated code ,and it worked well . [Here](https://microsoftapc-my.sharepoint.com/:u:/g/personal/v-xuelc_microsoft_com/EQ99O-p53vtMuq6JAdw4RM0BQl32Ql9Hp1-AM_QmH9l3Ng?e=erDDDZ) is my test demo , you could check the differences . — Xueli Chen, Nov 26 '19 at 03:18

score 2 · Accepted Answer · answered Nov 25 '19 at 20:01

2

This is a definite duplicate of how to upload a file and json data in postman

In your case, maybe you can try something like what is suggested in the following(https://stackoverflow.com/a/52748531/11226302)

answered Nov 25 '19 at 20:01

Shivam Puri

1,578
12
25

That is the only way it worked for me.Serializing the json into a string and sending it like a form `input` alongside my file. – Bercovici Adrian Nov 26 '19 at 07:55

Receiving multipart form-data json parameter null

1 Answers1