Describe objects with Property Expressions
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README.md

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propex expressions are strings that describe how you want to interact with an object.

Sound vague? That's intentional.

A Propex object provides an Abstract Syntax Tree (AST) of the expression parsed from the string. What you choose to do with that AST is completely up-to-you.

How about an example...

You can make expressions like this:

var Px = require('propex');
var px = Px("[{_id>id,name,skill}]0:3");

...and then maybe use it to copy/transform some data, like this:

var users = [
  { _id:"4e7e98", name:"Tom", skill:"nodejs" },
  { _id:"d8cc60", name:"William" },
  { _id:"03f5c2", name:"Mike", skill:"design" },
  { _id:"f1d2c9", name:"Gareth", skill:"marketing" }
];
console.log(px.copy(users));
//[ { id: '4e7e98', name: 'Tom', skill: 'nodejs' },
//  { id: 'd8cc60', name: 'William', skill: undefined },
//  { id: '03f5c2', name: 'Mike', skill: 'design' } ]

What is this for?

Syntax

Ok, the technical syntax above isn't super simple to understand.

It is ment to look JSON-like:

  • Objects use {}
  • Arrays use []

We borrow from python a bit to indicate Array ranges: 5:7
We borrow the '?' concept from regular expressions to indicate an item is optional.
We borrow the '>' from the unix command line to suggest redirection.

Objects

Use curly braces {} to begin and end an object definition. Create a comma separated list of property names between them. You can follow it with a meta markers if you like and then optionally use a '?' to flag it as optional.

//An object that must have a `username` and `password`.
//Optionally `dob` and `height`.
// ...and mark `dob` with `birth_date`
var px = Px("{username,password,dob>birth_date?,height?}")

Arrays

Arrays use the square brace [] syntax. To define a sub-propex that you want applied to the items of the array, place an object or array definition inside the braces. If you want to define something different for specific indices, just create a comma separated list of definitions (like you would for an object), but use the the index number instead of a property name. The indices can even be followed it with a meta marker and the '?' optional flag.

Additionally, just after the closing ']', you can add min:max numbers.

Example ranges and their meanings:
PPP,               min=  max=   Required
PPP?               min=  max=   Optional
PPP{PPP}?          min=  max=   Required
PPP[PPP]?          min=  max=   Optional
PPP[PPP]5?         min=5 max=   Optional
PPP[PPP]1:5?       min=1 max=5  Optional

Examples:

//an array is required
"[]"
//no different than above
"[{}]"


//an array that should have up-to 15 items in it
"[]0:15"

//an array that should have objects with and 'id' property
"[{id}]"

//same as above- but item[4] must have a url for some strange reason.
"[{id},4{id,url}]"

Meta Markers

Meta Markers simply mark a property with whatever meta string you want. If you do not specify a meta string to the right of the $ or >, the meta string will be the same as the property name.

Lets be picky... very picky

The simplest of utilities comes along with propex: A "picky" copy and rename utility.

By using a propex to copy another object, you can choose which properties you want to be copied to the new object. Using markers, you can even specify the name of destination property to copy to!

propex.copy(source [,modifiers])

  • source - The object you want to copy values from.
  • modifiers - An object with properties that match marker names. If a meta string is found in the propex but a corresponding modifier is not found, it will default to renaming the property to the meta string.
  • returns: The newly composed object

Meta Markers & Modifiers

You can use Meta Markers & Modifiers to transform the output of a property. The second parameter to the copy function, modifiers, allows you to specify an object with matching marker names that will modify the output during the copy process. If a modifier matching the meta string is not found, it will default to renaming the property to the value of the meta string.

Renaming properties:

var Px = require("propex");
var data = [
  {_id:"5452fb36c2a72b807d4e7e98"},
  {_id:"5452fb3fbf9df78086d8cc60"},
  {_id:"5452fb45ca6298808f03f5c2"},
  {_id:"5452fb4aab88b68098f1d2c9"}
];

var result = Px('[_id>mongo_id]').copy(data);

console.log(result);
//[ { mongo_id: "5452fb36c2a72b807d4e7e98" },
//  { mongo_id: "5452fb3fbf9df78086d8cc60" },
//  { mongo_id: "5452fb45ca6298808f03f5c2" },
//  { mongo_id: "5452fb4aab88b68098f1d2c9" } ]

Using modifiers for type coercion:

var Px = require("propex");
var data = {
  id:"670231",
  birth_date:"1986-03-16T08:00:00.000Z"
};

var modifiers = {
  Date: function(property, name, value, target) {
    target[name] = new Date(value)
  },
  Number: function(property, name, value, target) {
    target[name] = parseFloat(value);
  }
};

var result = Px('{id>Number,birth_date>Date}').copy(data, modifiers);

console.log(result);
//{ id: 670231,
//  birth_date: Sun Mar 16 1986 08:00:00 GMT+0000 (UTC) }

Examples

var Px = require("propex");
var data = {foo:8, bar: false, baz:{ dog:"bark", cat:[{type:"lion",sound:"rawr"},{type:"house",sound:"meow"}]}};

var propex = Px("{baz}");
var result = propex.copy(data);
console.log(JSON.stringify(result));
//{"baz":{"dog":"bark","cat":[{"type":"lion","sound":"rawr"},{"type":"house","sound":"meow"}]}}

var propex = Px("{baz{}}");
var result = propex.copy(data);
console.log(JSON.stringify(result));
//{"baz":{}}

var propex = Px("{baz{dog}}");
var result = propex.copy(data);
console.log(JSON.stringify(result));
//{"baz":{"dog":"bark"}}

var propex = Px("{baz{cat[{}]}}");
var result = propex.copy(data);
console.log(JSON.stringify(result));
//{"baz":{"cat":[{},{}]}}

var propex = Px("{baz{cat[{sound}]}}");
var result = propex.copy(data);
console.log(JSON.stringify(result));
//{"baz":{"cat":[{"sound":"rawr"},{"sound":"meow"}]}}

var propex = Px("{baz{cat[]3:}}");
var result = propex.copy(data);
console.log(JSON.stringify(result));
//{"baz":{"cat":[{"type":"lion"},{"type":"house"},null,null,null,null]}}

//... rename the `sound` property to `communication`
var propex = Px("{baz{cat[{sound>communication}]}}");
var result = propex.copy(data);
console.log(JSON.stringify(result));
//{"baz":{"cat":[{"communication":"rawr"},{"communication":"meow"}]}}

Examining objects

A propex object has a recurse(callback[, context]) function iterates over the propex calling the callback for each item.

propex.fields()

You can get a (mongo style 'fields' projection)[http://docs.mongodb.org/manual/tutorial/project-fields-from-query-results/#return-specified-fields-only] by calling the fields function of a Propex object.

var Px = require("propex");
var px = Px("{_id,foo,cat}");

console.log(px.fields());
//{ _id: 1, foo: 1, cat: 1 }

Installation

$ npm install propex

Technical definition

PROPERTYGROUP / ARRAYGROUP
PROPERTYGROUP = '{' *PROPERTIES '}'
ARRAYGROUP    = '[' [PROPERTYGROUP] / [INDEXITEMS] / *(PROPERTYGROUP 1*(',' INDEXITEMS) ']' [QUANTITY]
PROPERTIES    = PROPERTY *(',' PROPERTY)
INDEXITEMS    = INDEXITEM *(',' INDEXITEM)
PROPERTY      = 1*(ALPHA / DIGIT) [MARKER] [ARRAYGROUP / PROPERTYGROUP] [OPTIONAL]
INDEXITEM     = DIGIT [MARKER] [ARRAYGROUP / PROPERTYGROUP] [OPTIONAL]
QUANTITY      = DIGIT / (MIN ':') / (':' MAX) / (MIN ':' MAX)
MARKER        = ('$' / '>') *(ALPHA / DIGIT)
OPTIONAL      = '?'
MIN           = DIGIT
MAX           = DIGIT

...simple right?

License

The MIT License (MIT) Copyright (c) 2012-2014 William Kapke

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.