Evaluating MongoDB-like JSON Queries in PHP - php

Question

Consider the following (rather complicated) query expressed in this JSON object:
{
"name": "Kindle Fire",
"sale": true,
"price": {
"$gt": 199,
"$lt": 264
},
"price.vat": { // bogus, just to show $a['price.vat'] == $a['price']['vat']
"$lte": 1.2
},
"$or": {
"qty": {
"$gt": 30
},
"eta": {
"$or": {
"$lt": 3,
"$gt": 30
}
}
},
"countriesAvailable": {
"$in": [
"US",
"CA"
]
}
}
Objective
I want to parse that JSON so that it evaluates to the PHP equivalent of (where $a is my target data):
$a['name'] == 'Kindle Fire' &&
$a['sale'] == true &&
(
$a['price'] > 199 && $a['price'] < 264
) &&
$a['price']['vat'] <= 1.2 &&
(
$a['qty'] > 30 ||
(
$a['eta'] < 3 || $a['eta'] > 30
)
) &&
in_array($a['countriesAvailable'], array('US', 'CA'))
I have little experience building expression evaluators. My idea is to traverse the query from the innermost level to the outermost level, calling the corresponding MongoDB operator methods as needed.
Assuming $a matches the query, this would be the evaluation plan:
$query = array();
$query['name'] = true;
$query['sale'] = true;
$query['price'] = array();
$query['price']['$gt'] = true;
$query['price']['$lt'] = true;
$query['price']['vat'] = array();
$query['price']['vat']['$lte'] = true;
$query['$or'] = array();
$query['$or']['qty'] = array();
$query['$or']['qty']['$gt'] = false;
$query['$or']['eta'] = array();
$query['$or']['eta']['$or'] = array();
$query['$or']['eta']['$or']['$lt'] = true;
$query['$or']['eta']['$or']['$gt'] = false;
$query['countriesAvailable'] = array();
$query['countriesAvailable']['$in'] = true;
The second step:
$query = array();
$query['name'] = true;
$query['sale'] = true;
$query['price'] = array();
$query['price']['$gt'] = true;
$query['price']['$lt'] = true;
$query['price']['vat'] = true;
$query['$or'] = array();
$query['$or']['qty'] false;
$query['$or']['eta'] = array();
$query['$or']['eta']['$or'] true;
$query['countriesAvailable'] = true;
The third step:
$query = array();
$query['name'] = true;
$query['sale'] = true;
$query['price'] = true;
$query['$or'] = array();
$query['$or']['qty'] false;
$query['$or']['eta'] true;
$query['countriesAvailable'] = true;
The fourth step:
$query = array();
$query['name'] = true;
$query['sale'] = true;
$query['price'] = true;
$query['$or'] = true;
$query['countriesAvailable'] = true;
Since all the values are booleans the evaluation ends returning !in_array(false, $query, true).
If a better approach exists, let me know.
Problem: Accessing Parent Array Keys
I'm stuck trying to get the innermost the elements and the relevant (ignoring operators) array index path, for instance, if I use a RecursiveIteratorIterator I get the correct values for the first iteration:
$nodes = new ArrayIterator($query);
$iterator = new RecursiveArrayIterator($nodes);
$iteratorIterator = new RecursiveIteratorIterator($iterator, RecursiveIteratorIterator::LEAVES_ONLY);
print_r(iterator_to_array($iteratorIterator));
Array
(
[name] => Kindle Fire HD
[sale] => 1
[$gt] => 30
[$lt] => 3
[$lte] => 1.2
[0] => US
[1] => CA
)
However, it's of little use since I cannot be sure what $a index the keys are referring to, not to mention that the key values are being overwritten by latter entries and the fact that I can't change their values.
I've also tried playing with RecursiveArrayIterator, but without the hasParent() / getParent() methods it doesn't seem to give me much advantage over simply foreach'ing the array.
Any suggestions?

Answer 1

I quickly read your question it sounds like you want to visit leafs and know the key path to them.
so here:
$ritit = new RecursiveIteratorIterator(new RecursiveArrayIterator($myArray));
foreach ($ritit as $leafValue) {
$keyPath = array();
foreach (range(0, $ritit->getDepth()) as $depth) {
$keyPath[] = $ritit->getSubIterator($depth)->key();
}
// do something with $keyPath
// or
$hasParent = $ritit->getDepth() > 0;
$parentIter = $ritit->getSubIterator($ritit->getDepth() - 1);
$parentKey = $parentIter->key();
}