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Hi, I am getting this error in Blazor

JsonSerializationException: Cannot deserialize the current JSON array (e.g. [1,2,3]) into type 'DTO' because the type requires a JSON object (e.g. {"name":"value"}) to deserialize correctly.
To fix this error either change the JSON to a JSON object (e.g. {"name":"value"}) or change the deserialized type to an array or a type that implements a collection interface (e.g. ICollection, IList) like List<T> that can be deserialized from a JSON array. JsonArrayAttribute can also be added to the type to force it to deserialize from a JSON array.
Path '', line 1, position 1.

Here is my API Code

//var patientDiagnosis = await _context.PatientDiagnosis.FirstOrDefaultAsync(e=>e.Pid==Pid);
 var patientDiagnosis = await _context.PatientDiagnosis.Where(e => e.Pid == Pid).ToListAsync();
                if (patientDiagnosis == null)
                    logger.LogWarning($"Record Not Found:{nameof(GetPatientDiagnosis)}-ID:{Pid}");
                    return NotFound();
                return Ok(patientDiagnosis);

If I use FirstOrDefaultAsync API to show data in a Blazor form, but if I use Where then it shows the above error. But in Swagger or Postman API it is working fine.

Anybody have any idea please?

What I have tried:

I have no idea how to solve this in a Blazor app because it works in Postman and the error shows only when I use

await _context.PatientDiagnosis.Where(e => e.Pid == Pid).ToListAsync();
Updated 26-Jan-22 6:08am

1 solution

Your API client is expecting your endpoint to return a single record.

You cannot change the endpoint to return a list of records and expect it to magically work.

Either add a different endpoint for returning the list of records, or change your client code so that it deserializes the response as a list of records instead of a single record.
Share this answer
Member 13291196 26-Jan-22 10:48am    
Thank you richard for your valuable response. can you please suggest any idea? i use Nswag Studio for Generate Client code
Richard Deeming 26-Jan-22 11:28am    
I have already told you what you need to do - either add a new endpoint to return the list of records, or update your client code to deserialize the response from the existing endpoint correctly.
Member 13291196 26-Jan-22 11:34am    
yeah, I create another Endpoint from the Controller side. but from client-side its showing the same error
Richard Deeming 26-Jan-22 11:37am    
Then either your initial endpoint is still returning a list when your client expects it to return a single record, or your client is expecting the new endpoint to return a single record.

The client needs to match the endpoint - either the endpoint returns a single record, and the client deserializes a single record; or the endpoint returns a list of records, and the client deserializes a list of records.

As I keep trying to explain to you, the error from your question is what you get when the endpoint returns a list of records, and the client expects a single record.
Member 13291196 26-Jan-22 11:42am    
Got It Richard Thankyou

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