The string returned from the Controller is not recognized as a valid JSON object

When attempting to retrieve a string from a JSON response, I encounter an error:

SyntaxError: Unexpected token c in JSON at position

In the controller, a GUID is returned as a string from the database:

[HttpPost("TransactionOrderId/{id}")]
public async Task<string> TransactionOrderId(int id)
{
    return await this._service.GetTransactionOrderId(id);
}

In my Angular 2 application, there is an issue with parsing the server's response when subscribing to the provider:

this.meetingsProvider.getTransactionOrderId(this.meetingId).subscribe((transactionId: string) => {
    this.transactionOrderId = transactionId;
});

The provider code is as follows:

getTransactionOrderId(meetingId: number): Observable<string> {

    const headers = new Headers();
    headers.append('Content-Type', 'application/json');

    return  this.http.post(`${this.apiUrl}/${this.route}/transactionOrderId/${meetingId}`, null, {
        headers: headers
    }).map(res => <string>res.json());
}

Upon receiving the transaction order ID response from the server, the format appears as:

status: 200
statusText: "OK"
type: 2
url: "http://localhost/api/meetings/transactionOrderId/4"
_body: "0c290d50-8d72-4128-87dd-eca8b58db3fe"

While other API calls using similar code to return boolean values work fine, attempting to return a string triggers a parsing error. Why does this happen?

Answer №1

The reason you are receiving an error is because the content provided is not a valid JSON object. To create a valid JSON object, it must start with { and end with }.

To ensure successful JSON deserialization, you can use the following code snippet:

public async Task<JsonResult> TransactionOrderId(int id)
{
    return Json(await this._service.GetTransactionOrderId(id));
}

Keep in mind that if you return anything other than a string, ASP.NET Core will automatically serialize it into JSON format using the default serializer.

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