Build complex rules, serialize them as JSON, and execute them in PHP
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Jeremy Wadhams
Jeremy Wadhams Adding substr support
Latest commit 6d38c14 Oct 5, 2017

README.md

json-logic-php

This parser accepts JsonLogic rules and executes them in PHP.

The JsonLogic format is designed to allow you to share rules (logic) between front-end and back-end code (regardless of language difference), even to store logic along with a record in a database. JsonLogic is documented extensively at JsonLogic.com, including examples of every supported operation and a place to try out rules in your browser.

The same format can also be executed in JavaScript by the library json-logic-js

Examples

A note about types

This is a PHP interpreter of a format designed to be transmitted and stored as JSON. So it makes sense to conceptualize the rules in JSON.

Expressed in JSON, a JsonLogic rule is always one key, with an array of values.

{"==" : ["apples", "apples"]}

PHP has a way to express associative arrays as literals, and no object equivalent, so all these examples are written as if JsonLogic rules were decoded with json_decode's $assoc parameter set true, e.g.

json_decode('{"==" : ["apples", "apples"]}', true);
// ["==" => ["apples", "apples"]]

The library will happily accept either associative arrays or objects:

$rule = '{"==":["apples", "apples"]}';

//Decode the JSON string to an array, and evaluate it.
JWadhams\JsonLogic::apply( json_decode($rule, true) );
// true

//Decode the JSON string to an object, and evaluate it.
JWadhams\JsonLogic::apply( json_decode($rule, false) );
// true

Simple

JWadhams\JsonLogic::apply( [ "==" => [1, 1] ] );
// true

This is a simple test, equivalent to 1 == 1. A few things about the format:

  1. The operator is always in the "key" position. There is only one key per JsonLogic rule.
  2. The values are typically an array.
  3. Each value can be a string, number, boolean, array, or null

Compound

Here we're beginning to nest rules.

JWadhams\JsonLogic::apply(
	[ "and" => [
		[ ">" => [3,1] ],
		[ "<" => [1,3] ]
	] ]
);
// true

In an infix language (like PHP) this could be written as:

( (3 > 1) and (1 < 3) )

Data-Driven

Obviously these rules aren't very interesting if they can only take static literal data. Typically JsonLogic::apply will be called with a rule object and a data object. You can use the var operator to get attributes of the data object:

JWadhams\JsonLogic::apply(
	[ "var" => ["a"] ], // Rule
	[ "a" => 1, "b" => 2 ]   // Data
);
// 1

If you like, we support syntactic sugar on unary operators to skip the array around values:

JWadhams\JsonLogic::apply(
	[ "var" => "a" ],
	[ "a" => 1, "b" => 2 ]
);
// 1

You can also use the var operator to access an array by numeric index:

JWadhams\JsonLogic::apply(
	[ "var" => 1 ],
	[ "apple", "banana", "carrot" ]
);
// "banana"

Here's a complex rule that mixes literals and data. The pie isn't ready to eat unless it's cooler than 110 degrees, and filled with apples.

$rules = [ "and" => [
	[ "<" => [ [ "var" => "temp" ], 110 ] ],
	[ "==" => [ [ "var" => "pie.filling" ], "apple" ] ]
] ];

$data = [ "temp" => 100, "pie" => [ "filling" => "apple" ] ];

JWadhams\JsonLogic::apply($rules, $data);
// true

Always and Never

Sometimes the rule you want to process is "Always" or "Never." If the first parameter passed to JsonLogic::apply is a non-object, non-associative-array, it is returned immediately.

//Always
JWadhams\JsonLogic::apply(true, $data_will_be_ignored);
// true

//Never
JWadhams\JsonLogic::apply(false, $i_wasnt_even_supposed_to_be_here);
// false

Installation

The best way to install this library is via Composer:

composer require jwadhams/json-logic-php

If that doesn't suit you, and you want to manage updates yourself, the entire library is self-contained in src/JWadhams/JsonLogic.php and you can download it straight into your project as you see fit.

curl -O https://raw.githubusercontent.com/jwadhams/json-logic-php/master/src/JWadhams/JsonLogic.php