Understanding difference between "@property=='<property_key>" and "@.<property_key>"

[sankalpn]

While trying out different filters, I noticed the following:

1. Filtering with @Property works intuitively.
   JSONPath({ path: '$.[?(@property === "appName" && @ === "app1")]^', json: { "version": 1, "appName": "app1" }, wrap: false });
   The json passes filter and gets returned
   {"version":1,"appName":"app1"}
2. The same thing with @.<property_name> filters out above json.
   JSONPath({ path: '$.[?(@.appName === "app1")]^', json: { "version": 1, "appName": "app1" }, wrap: false });
   This returns
   undefined

Is this behaviour expected? If yes, can we add a couple of more examples to documentation?

[brettz9]

In your second example:

JSONPath({ path: '$.[?(@.appName === "app1")]^', json: { "version": 1, "appName": "app1" }, wrap: false });

...you wouldn't want the parent selector (^), as that would be looking above root (since that filter is on an object, and that object happens to be root.

But even without the parent selector, the expression still doesn't match.

I think the problematic aspect here is that filters apply to children, and there is thus no apparent way to use the object-selectors in a way that matches root (though as per your first example, and as per #118, one can use property selectors along with the parent selector to match root because property selectors are looking at children not at the containing parent object).

Note that this gets the object (albeit in an array):

    const result = jsonpath({
        path: '$.[?(@.appName === "app1")]',
        json: {a: {version: 1, appName: 'app1'}}, wrap: false});
    assert.deepEqual(result, [{version: 1, appName: 'app1'}]);

That works because the object is no longer at root, and the comparison is on the children.

So I think the real issue here is that we need a type of filter which checks the targeted item directly rather than its children (or at least so that we might allow reaching above root in the case of filters, e.g., $.^[?(@.appName === "app1")]). (That currently also gets a bad error, this._trace(...).filter is not a function.)