#@deckyard/jsonpath

RFC 9535 JSONPath queries over json.Value. The whole RFC is covered: name, wildcard, index, slice and filter selectors, descendant segments, comparisons, && || !, and the functions length, count, match, search and value. Every case of the official JSONPath Compliance Test Suite passes. Pure computation: no capability, and it runs on jennifer-tiny.

#Conventions

Snippets assume this import:

import "@deckyard/jsonpath/" as jsonpath;

def doc as json.Value init json.decode(fs.readString("store.json"));
for (def title in jsonpath.query($doc, "$.store.book[?@.price < 10].title")) {
    io.printf("%s\n", json.asString($title));
}

Three ways to ask, for one query string:

jsonpath.compile parses a query once; jsonpath.find runs it on a document and returns all three for each node as a Match. Results come in the order RFC 9535 defines; an object's members in document order.

#Changing what a query found

The pointers feed the json writers. Removing shifts the later elements of an array, so remove from the last pointer to the first:

def ptrs as list of string init jsonpath.paths($doc, "$..book[?@.price > 10]");
def i as int init len($ptrs) - 1;
while ($i >= 0) {
    $doc = json.remove($doc, $ptrs[$i]);
    $i = $i - 1;
}

#Errors

Every failure is Error{kind: "jsonpath"}. A query that is not valid RFC 9535 fails in compile, query, paths and normalizedPaths with the reason and the position:

jsonpath: only a singular query can be compared at position 9 of "$[?@.* == 1]"

That includes the type rules of RFC 9535 section 2.4.3: an unknown function, a wrong argument count, a query that can select several nodes where one value is needed, a function returning a value used as a test. isValid asks without throwing. A query over its node limit fails while it runs; see Untrusted queries.

A valid query never fails on a document: a selector that does not apply (a name on an array, an index past the end) selects nothing.

#Requirements

Jennifer 0.25.0 or newer, default or jennifer-tiny binary.