How to catch BadHttpRequestException thrown by invalid json body

Question

Im playing abit with the .NET minimal API. Trying to catch this exception when Im passing "Price" as a string I've got my DTO as follows:

public record TransactionCreateDto    
{
    public string Description { get; init; } = String.Empty;
    public string Store { get; init; } = String.Empty; 
    public double Price { get; init; }
    public string Date { get; init; } = String.Empty;
    public int PaymentTypeId { get; init; }
    public int CategoryId { get; init; }
    public bool Seen { get; init; }
}

Here is the flow:

...
app.MapPost("/transactions", TransactionsAPI.InsertTransaction);
...

And he insert transaction function:

public static async Task<IResult> InsertTransaction(TransactionCreateDto transactionDto, ITransactionRepository repo)
{
    try 
    {
    ...
    } 
    catch (Exception ex)
    {
    ...
    }
}

Im sure there is a correct way to catch this exception. Thanks alot!

That exception happens before the handler method is invoked. You can look into [custom exception handler](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/error-handling?view=aspnetcore-6.0) or manually parsing dto from request. — Guru Stron, Aug 17 '22 at 17:07

score 1 · Answer 1 · answered Aug 18 '22 at 08:54

Since the exception is happening before your function is getting called, I prefer the following approach. It's not 100% by the playbook, but gives much more flexibility.

Lets assume this is your original signature:

public static async Task<IResult> InsertTransaction(TransactionCreateDto transactionDto)

So instead of getting the DTO, try to get JObject.

public static async Task<IResult> InsertTransaction(Jobject json)
{
    try
    {
        var m = JsonConvert.DeserializeObject<TransactionCreateDto>(json);
    }
    catch(SomeSpecificException es)
    {
      
    }
    catch(Exception e)
    {
    }
}

Thanks alot! Ill try this approach aswell! – Mark Poliatskin Aug 18 '22 at 13:47 — Mark Poliatskin, Aug 18 '22 at 13:47
This will still throw if the json itself is invalid. – Guru Stron Aug 18 '22 at 13:49 — Guru Stron, Aug 18 '22 at 13:49

Guru Stron · Answer 2 · 2022-08-18T13:59:00.443

If the situation you are trying to handle is that passed string is a valid number (i.e. you want to allow this), one option is to allow the serializer to handle such cases by configuring it (see customizing json binding doc and JsonNumberHandling enum):

builder.Services.Configure<JsonOptions>(options =>
{
    options.SerializerOptions.NumberHandling = JsonNumberHandling.AllowReadingFromString;
});

Otherwise depending on the use case you can either handle the request parsing manually (custom serializer, BindAsync convention, or just from the request) or use custom error handler (if you want just to process the error in some custom way).

How to catch BadHttpRequestException thrown by invalid json body

2 Answers2