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