JSON Operator

Perform efficient path based operations on JSON Objects (or most Javascript data object).

Uses jsonpath with new delete option for apply.

Install

npm i json-operator --save

API

Note: The arguments indent, path and opts are always optional.

Constructor

• constructor(target, {path, jsonpath, mergeFun, createMerge})

Setters and getters

• .path : default operator path
• .target : target object
• .jp : jsonpath engine
• .createMerge : function(opts)

createMerge can be set to factory function which returns custom merge function used by merge if present. The opts will be the options passed to merge enriched with targetObj and mergeObj

Getters

• .history : history list of path and operation made
• .result : modified target object
• .lastPath : last path mutation applied

Display

• targetAsStr(indent = 2) : get prettified string of target obj
• display(indent, logger) : display prettified string of target obj using logger (default console.log)

Read values

• query(path) : get all match results in list
• value(path) : get first match result
• parent(path) : parent of first match

Path operation scope*

• with(path) : set withPath used in new operations scope
• withSame() : use lastPath as withPath in new operations scope
• and() : alias to withSame
• done() : exit current operation scope

Mutations

opts is an optional argument which may contain:

• path : to override current scope path
• condition : function to be called with node value and context (ie. parent and key) to decide if mutation/action should be performed.

This condition function has the signature:

function(value, {parent, key}) : boolean

Insert

• concat(insertObjs, opts = {}) : concatenate object(s) at the end of parent Array
• prepend(insertObj, opts = {}) : prepend object before matching node
• append(insertObj, opts = {}) : append object after matching node
• insertAt(insertObj, key) : insert object at key on target object

Delete

• delete(opts = {}) : delete matches
• splice(opts = {}) : splice on target object (start, deleteCount, insertObj options)

Set

• overwrite(obj, opts = {}) : set match to new object

Merge

• merge(obj, opts = {}) : merge matches with new object
• deepMerge(obj, opts = {}) : deep merge matches with new object
• reverseMerge(obj, opts = {}) : merge matches with new object

Delegation (general purpose)

• apply(fn, path) : delegates to jsonpath.apply
• filter(fn, path) : delegates to jsonpath.filter

Flatten/Unflatten

Use the flatten and unflatten methods. First you must set the flattener to use, such as flat or soon to be flat2 (WIP)

Normalize

Use the normalize method which uses normalizr

For flatten and normalize usage examples, see the Changelog.md or the documentation for each module (flat and normalizr).

All mutators can be chained beautifully :)

let finalResult = operator
  .delete({path: delPath.x})
  .merge(obj, {path: mergePaths.a, condition: mySpecialCondition})
  .withSame() // use latest path for new scope
    .overwrite({x: 2}) // overwrite using latest scope path
    .merge(partials[0], {path: mergePaths.b}) // merge using custom path
    .and() // use latest path for new scope
      .merge(objX) // reusing latest path
      .with(specialPath) // create scope with path
        .merge(partials[1]) // merge using scope path
        .with(sweetPath) // create inner scope path
          .merge(partials[2]) // merge using current scope path
        .done() // close current scope
      .done()
    .done()
  .done()
  .result;

You can add your custom functions directly to the operator object or the class JsonOperator.prototype.

Usage

Given the following book store:

{
  "store": {
    "book": [ 
      {
        "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      }, {
        "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
      }, {
        "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
      }, {
         "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
      }
    ],
    "bicycle": {
      "color": "red",
      "price": 19.95
    }
  }
}

Note: Books are indexed from 0 as normal, so book [2] is the 3rd book in the list.

We perform the following operations to:

• get the value of book [2]
• get the value of book [3]
• set the default opertor path to book [3]
• overwrite book 3 with book [2]
• merge {price:100} onto book [3]
• reverse order merge {rating: 4} onto book [3]
• delete book [3]
• display full target object after operations

Full API example

const store = require('./store')
const operator = new JsonOperator(store)
 
let paths = {
  book2: '$..book[2]',
  book3: '$..book[3]'
}
 
// query for all matching path
let book2results = operator.query(paths.book2);
console.log('original book 2', book2results)
 
// get the first match for book 2
let book2val = operator.value(paths.book2);
console.log('original book 2 value', book2val)
 
// let book2par = operator.parent(paths.book2);
// console.log('original book 2 parent', book2par)
 
// get the first match for book 3 
let book3 = operator.value(paths.book3);
console.log('original book 3', book3)
 
// set default path to use for the following ops
operator.path = paths.book3;
 
// overwrite book3 with book2
operator.overwrite(book2val)
let book3Set = operator.value(); 
 
console.log('original book 3', book3)
console.log('book 3 set', book3Set)
 
// overwrite book2 with value found at book3
operator.merge({price: 100})
let book3Merged = operator.value()
 
console.log('original book 3', book3)
console.log('book 3 set', book3Set)
console.log('book 3 set', book3Merged)
 
// operator.merge({price: 100}, {reverse: true})
operator.deepMerge({rating: 4}, {reverse: true, path: mergePath})
operator.reverseMerge({rating: 4})
operator.reverseMerge({rating: 4}, {path})
 
operator.delete()
let book3deleted = operator.value()
console.log('book 3 deleted', book3deleted)
console.log('store after all operations', operator.targetAsStr())

Custom merge

You can define a custom merge function as follows:

// return merge function dependent on option .admin setting
operator.createMerge = (opts) => {
  return (opts.admin) ? fullMerge : partialMerge; 
}
 
// do full merge
operator.merge({admin: true})
 
// return merge function dependent on whether role of target object (a User) is 'admin'
operator.createMerge = (opts) => {
  return (opts.targetObj.role === 'admin') ? fullMerge : partialMerge; 
}
 
operator.target = {
  name: 'kris',
  role: 'admin'
}
 
// do full merge
operator.merge();
 
operator.target = {
  name: 'sandy',
  role: 'guest'
}
 
// do partial merge
operator.merge();

The example demo (excluding use of createMerge) can be found in /examples/demo.js in the repo.

Set alternative jsonpath engine

You can now also set an alternative jsonpath engine.

const fastpath = require('fastpath');
operator.jp = fastpath;

Note: Some jsonpath alternatives don't yet have a filter function (for delete) and be fully compatible. You might however be able to add filter (and apply) from jsonpath?

fastpath.filter = jsonpath.prototype.filter;

Advanced usage

• through2
• stream-handbook

Example:

var all = []
 
fs.createReadStream('./data.json')
  .pipe(split())
  .pipe(through2.obj(function (obj, enc, callback) {
    const operator = new JsonOperator(obj)
    // some JSON operations
    // ...
    let data = operator.result;
    this.push(data)
    callback()
  }))
  .on('data', function (data) {
    all.push(data)
  })
  .on('end', function () {
    doSomethingSpecial(all)
  })

To operate efficiently on a folder with json file perhaps use readdirp to read directory as a stream. See next example for inspiration.

Mongoose streaming example

querystream

const paths = {
  // ...
  userRole: '$.user.role'
};
 
const jsonTransformStream = new JsonTransformStream({ paths });
 
Model.find().stream().pipe(jsonTransformStream).pipe(ctx.body);

const Transform = require('stream').Transform

module.exports = class JsonTransformStream extends Transform {
  constructor(options = {}) {
    this.operator = new JsonOperator();
    this.paths = options.paths;
    this.objs = options.objs;
  }

  // do some user role operations!
  operateOn(obj) {
    this.operator.target = chunk;
    if (obj.user) {
      this.operator.merge(this.objs.role, {path: this.paths.userRole})
    }
    this.push(this.operator.result);
  }

  _transform(chunk, encoding, done) {
    this.operateOn(chunk)
    done();
  }

  _flush(done) {
      done();
  }
}

Alternatives

Some alternative jsonpath transformers

• jsonpath-plus
• jsonpath-transform
• jsonpath-object-transform
• jsonpath-rep with replacement

Would be nice if we could combine the best of all ;)

JSON path alternative

• jsonave
• fastpath

Misc

• jsonpath-to-dot

Licences

MIT

Kristian Mandrup [e-mail] 2016