json-logic-dart

This parser accepts JsonLogic rules and executes them in Dart.

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.

This is not intended to be an optimized representation of each operation, but instead is intended to reproduce the functionality of JsonLogic's JavaScript port in a line-by-line fashion (comments and all). The focus is on portability rather than efficiency.

Installation

To parse JsonLogic rules in a Dart codebase, install this library via pub.

Examples

Simple

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 (non-associative), or null

Compound

Here we're beginning to nest rules.

jsonLogic.apply(
  {"and" : [
    { ">" : [3,1] },
    { "<" : [1,3] }
  ] }
);
// true

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

( (3 > 1) && (1 < 3) )

Data-Driven

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

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:

jsonLogic.apply(
  { "var" : "a" },
  { a : 1, b : 2 }
);
// 1

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

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.

var rules = { "and" : [
  {"<" : [ { "var" : "temp" }, 110 ]},
  {"==" : [ { "var" : "pie.filling" }, "apple" ] }
] };

var data = { "temp" : 100, "pie" : { "filling" : "apple" } };

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 is a non-object, non-associative-array, it is returned immediately.

//Always
jsonLogic.apply(true, data_will_be_ignored);
// true

//Never
jsonLogic.apply(false, i_wasnt_even_supposed_to_be_here);
// false