Eval length() function returns wrong answer after filtering array

[Joey29-1]

The length() function in Eval() does not return the correct answer if the array of objects is filtered.

In the code snippet below, there is no element in $.items that matches the array filtering condition, but the length of the resulting array is still evaluated to 1 instead of 0.

json := []byte(`
{
  "items": [
    {
      "price":1, 
      "type": "A"
    }, 
    {
      "price":2, 
      "type": "B"
    }, 
    {
      "price":3, 
      "type": "C"
    }
  ]
}`)

root, err := ajson.Unmarshal(json)
if err != nil {
  panic(err)
}
res1, err := ajson.Eval(root, `length($.items[?(@.type == "D")])`)
if err != nil {
  panic(err)
}
fmt.Printf("Result: %+v", res1.MustNumeric()) // Expected: 0, Actual: 1

res2, err := ajson.Eval(root, `length($.items[?(@.type == "A")])`)
if err != nil {
  panic(err)
}
fmt.Printf("Result: %+v", res2.MustNumeric()) // Expected: 1, Actual: 2

res3, err := ajson.Eval(root, `length($.items[?(@.type == "A" || @.type == "B")])`)
if err != nil {
  panic(err)
}
fmt.Printf("Result: %+v", res3.MustNumeric()) // Expected: 2, Actual: 2

[Joey29-1]

What I have figured out after tracing the code:

• If none of the elements match the array filter condition, the resultant Node has NodeType Null. According to the implementation of the length() function, a value of 1 is returned.
• On a similar vein, if only 1 element matches the filter condition, the resultant Node has NodeType Object (I thought it was Array). The length() function then returns node.Size().

[spyzhov]

Thank you for sharing this! I will try to prepare the fix today ASAP.

[spyzhov]

Fixed in v0.9.2

[tpoxa]

BTW why the length of null is 1? @spyzhov
How can I check if an array has elements while array itself could be null?

[spyzhov]

Good point... length of the element is equal to 1, for the reason that the value that you select is always the array, as soon as any JSONPath response is array.

What you are asking about... I suppose I should add some new functions, like is_*type*. I will try to add it asap, or feel free to suggest changes :-)

[spyzhov]

@tpoxa, I added is_*type* functions in v0.9.5

[tpoxa]

thanks @spyzhov