Handling thrown exceptions from WebApi with BreezeJs executeQuery (Unhandled rejection reasons)

Question

I am using Breeze.js and Q.js within my MVC app.

I currently have an action on my webApi

public IQueryable<Myobject> doMyAction()

This can do 2 things:

Return a collection of objects (if the user is allowed)
Throw a HTTP Exception (if the user is not allowed) (It may not be an "unauthorised" , this is just an example)

throw new HttpResponseException(Request.CreateResponse(HttpStatusCode.Unauthorized, "Not Allowed"));

This action gets called from javascript with breeze with:

var query = EntityQuery.from('doMyAction');

    // execute the query
    dcCore.manager.executeQuery(query)
      .then(querySucceeded)
      .fail(dcCore.queryFailed);

If the user is authorised and the logic is true, then I connect to my DB and return a nice list of Myobject() and everything is fine.

However, if I do a throw exception to say they are unauthorised, then in the console I get my 401 (Unauthorised) and the message:

[Q] Unhandled rejection reasons (should be empty):

This happens before it hits the .fail() function.

I also tried putting a try/catch around the whole execute bit, hoping that I would catch an error, but had no luck.

I can see why this is happening in theory, as I am not returning something that executeQuery is expecting (In fact, im not returning at all, i'm throwing!), however,

-actual question

how should I handle returning errors from the webApi with breeze, without doing something like extending the model?

The only thing I am yet to try is to make my web API return a type of dynamic, or generic object, but this doesn't feel like the best solution.

Jay Traband Jay Traband · Accepted Answer · 2015-04-16T17:21:40

You have two approaches for this, the first is to simply throw an simple exception directly in your query method, i.e. something like this:

[HttpGet]
public IQueryable<Customer> CustomersStartingWith(string companyName) {
  if (companyName == "null") {
    throw new Exception("nulls should not be passed as 'null'");
  }
  ...
}

Or, if you want slightly more control over the HTTPResponse you can do the following:

[HttpGet]
public IQueryable<Customer> CustomersWithHttpError() {
  var responseMsg = new HttpResponseMessage(HttpStatusCode.NotFound);
  responseMsg.Content = new StringContent("Custom error message");
  responseMsg.ReasonPhrase = "Custom Reason";
  throw new HttpResponseException(responseMsg);
}

Note that for a Save operation as opposed to the Query operations described above, the best approach is to throw an EntityErrorsException. (see documentation), although throwing a simple exception will still work.

Hope this helps.

Handling thrown exceptions from WebApi with BreezeJs executeQuery (Unhandled rejection reasons)

-actual question

1 Answers