Issue in management of alternates [q, r, ...]

[frmichel]

Hi again,

I have a second question.
Here is JSON document:
{ "p":{
"s": { "u": "su" },
"t": { "u": "tu" }
}}

Expression $.p.['t'].u returns "tu" => ok.
Expression $.p.['s', 't'].u returns nothing, I'd expect "su" and "tu".

Another document : { "p": ["valp", "valq", "valr"] }
Expression $.p[?(@[0] == 'valp')] returns nothing, I would expect ["valp", "valq", "valr"]
Expression $.p[?(@.length == 3)] returns nothing, I would expect ["valp", "valq", "valr"]

Am I mistaken or is there actually a bug somewhere?

Thx,
Franck.

[kallestenflo]

The first issue:

$.p.['s', 't'].u returns nothing

In the current implementation you can only select multiple properties ['s', 't'] as the last part of a path. $.p.['s', 't'] works fine.

The second issue:

In the path $.p[?(@[0] == 'valp')] the @ represents the current element in the array and since your example is not an array of arrays this does not work. The intended use is $.p[?(@ == 'valp')]

Hope that makes sense.

[frmichel]

Hi, thx for your reply.

In the current implementation you can only select multiple properties ['s', 't'] as the last part of a path. $.p.['s', 't'] works fine.

Ok for the limitation of field alternatives. Good to know.

About the use of @ indeed I'm afraid I'm confused with what "current element" really means depending on wether it is used in expressions [?(...)] or [(...)].
In the examples of the main project's README there is this example:

$..book[?(@.isbn)] All books with an ISBN number

Here indeed book is an array and @ refers to elements of the array.
Does this mean that expression p[?(...)] only works when p is an array?

But then, how would you write an expression to "select field p of any document in which there exists field q"? This was my initial intention when I wrote p[?(@.q)].

In $.p[(...)] the expression in () is a calculated index, assuming that p is necessarily an array.
In the examples of the main project's README there is this example:

$..book[(@.length-1)] : The last book

In that case @ refers to book, not to its elements. That is quite confusing compared to the [?()], isn't it?

Thx in advance, I really need to make sure I understand this! ;-)

Franck.

[kallestenflo]

Expressions like [?(...)] can be used in the following contexts:

• Filter array $.store.book[?(@.category == 'fiction')]
• Scan $..[?(@.category == 'fiction')]
• Match $.store.book[1][?(@.category == 'fiction')]

But then, how would you write an expression to "select field p of any document in which there exists >field q"? This was my initial intention when I wrote p[?(@.q)].

That can not be done.

$..book[(@.length-1)] : The last book

In that case @ refers to book, not to its elements. That is quite confusing compared to the [?()], isn't it?

I agree this is confusing. Think I will remove support for (@.length-1) because it can be achieved via $..book[-1:].

[zline]

@frmichel first case now works as you expect

[frmichel]

@zline Great thx!

[kallestenflo]

Don't think I will get any further with this. Current state is described below and I think it works as expected. Thoughts on this?

@Test
public void issue_114_a() {
    String json = "{ \"p\":{\n" +
            "\"s\": { \"u\": \"su\" }, \n" +
            "\"t\": { \"u\": \"tu\" }\n" +
            "}}";

    List<String> result = JsonPath.read(json, "$.p.['s', 't'].u");
    assertThat(result).containsExactly("su","tu");
}

@Test
public void issue_114_b() {
    String json = "{ \"p\": [\"valp\", \"valq\", \"valr\"] }";

    List<String> result = JsonPath.read(json, "$.p[?(@ == 'valp')]");
    assertThat(result).containsExactly("valp");
}

@Test
public void issue_114_c() {
    String json = "{ \"p\": [\"valp\", \"valq\", \"valr\"] }";

    List<String> result = JsonPath.read(json, "$.p[?(@[0] == 'valp')]");
    assertThat(result).isEmpty();
}

@Test(expected = InvalidPathException.class)
public void issue_114_d() {
    JsonPath.read("[]", "$..book[(@.length-1)] ");
}