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Editorial Team
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Asked: 2026-06-17T21:03:20+00:00

I’m attempting to use Breeze to query a ASP.Net Web API endpoint and the

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I’m attempting to use Breeze to query a ASP.Net Web API endpoint and the query fails – with the data object containing:

internalError: TypeError
arguments: Array[2]
0: "createCtor"
1: null
length: 2
__proto__: Array[0]
get message: function () { [native code] }
get stack: function () { [native code] }
set message: function () { [native code] }
set stack: function () { [native code] }
type: "non_object_property_load"

The data object has a message (and responsetext) property which contains the full json response from the query which looks ok and the metadata thats been generated matches the response – it also records status 200 for the response

So I’m guessing there is some kind of issue mapping the response to an object on the client side?

I’m using the NuGet package for Breeze version 0.85.2

I can get the sample ToDo project to run fine on the same environment

My project does use domain objects, contexts etc all from different assemblies and namespaces but I understood thats supported in this version?

Also that one of the properties is an enum – in the metadata this is defined as {\"name\":\"State\",\"type\":\"Edm.Self.State\",\"nullable\":\"false\"}] but in the response is comes through as an integer

Looking for tips on how to debug this further on the client side

Update

comparing the working sample with my code, the error looks to be coming from this function:

/**
Returns the constructor for this EntityType.
@method getEntityCtor
@return {Function} The constructor for this EntityType.
**/
ctor.prototype.getEntityCtor = function () {
    if (this._ctor) return this._ctor;
    var typeRegistry = this.metadataStore._typeRegistry;
    var aCtor = typeRegistry[this.name] || typeRegistry[this.shortName];
    if (!aCtor) {
        var createCtor = v_modelLibraryDef.defaultInstance.createCtor;
        if (createCtor) {
            aCtor = createCtor(this);
        } else {
            aCtor = function() {
            };
        }
    }
    this._setCtor(aCtor);
    return aCtor;
};

The defaultInstance property on v_modelLibraryDef is undefined in my running code – what am I missing on the configuration of breeze for that to happen?

Update 2 – Resolved but why

Ok so I got this working – I was missing a reference to knockout (which I was planning to use but hadn’t got that far) – I was a little bit misled by the breeze prerequisites which don’t mention knockout so if anyone can explain how I could have got this working without knockout and if its a bug then the points are yours

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1 Answer

  1. Editorial Team

    Sorry you struggled Richard. We’ll try to learn from it and spare the next person the pain you endured.

    FWIW, we do not say that Knockout is a prerequisite … because KO is not a prerequisite. You can use Angular or Backbone instead and we anticipate other alternatives in future.

    We don’t want to drown you in configuration options when you’re just learning Breeze. So we picked KO as the default model library (just as jQuery is the default AJAX provider and Web API is the default “dataservice” technology). We say so in numerous places; prerequisites looks like another good place to mention it.

    As it happens, you intended to go with KO anyway so no configuration would have been necessary. Most folks start with something like the MVC template which includes KO and loads it for you in the Index.cshtml.

    Apparently you started from a clean slate (“ASP Empty Web Application” perhaps?). The Breeze Web API NuGet package strives to be spare and therefore does not include KO. We figured (incorrectly) that you would add it yourself … in the right script order … if you wanted to use KO. Clearly we could do a better job of documenting this particular development path … especially as we like it so much ourselves. Thanks for pointing it out.

    The other problem is that the exception was not helpful. You can see from other attempts to answer your question that even folks with Breeze experience couldn’t recognize what was wrong. We’ll look to see if we can detect the missing script a little earlier and throw an exception with a better message.

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