mingo

MongoDB query language for in-memory objects

Install

$ npm install mingo

Features

Supports Dot Notation for both <array>.<index> and <document>.<field> selectors
Query and Projection Operators
Aggregation Framework Operators
Support for adding custom operators using mingo.addOperators
Match against user-defined types
Support for aggregaion variables
- $$ROOT,$$CURRENT,$$DESCEND,$$PRUNE,$$KEEP,$$REMOVE
ES6 module compatible
Support integrating with custom collections via mixin
Query filtering and aggregation streaming.

For documentation on using query operators see mongodb

Documentation

Usage

// Use as es6 module
import mingo from 'mingo'

// or vanilla nodeJS
const mingo = require('mingo')

Change in 4.x.x

The $where operator is not loaded by default and must be explicitly registered if required. See documentation for preferred alternatives.

Changes in 3.0.0

Default exports and operators

The default export of the main module only includes Aggregator, Query, aggregate(), find(), and remove().

Only Query and Projection operators are loaded by default when using the main module. This is done using the side-effect module mingo/init/basic, and also automatically includes pipeline operators $project, $skip, $limit, and $sort.

If your application uses most of the available operators or you do not care about bundle size, you can load all operators as shown below.

// Note that doing this effectively imports the entire library into your bundle and unused operators cannot be tree shaked
import 'mingo/init/system'

Or from the node CLI

node -r 'mingo/init/system' myscript.js

Custom Operators

The addOperators function for registering custom operators and helper constants have been moved to mingo/core. The constants OP_XXX have been deprecated and replace with an enum type OperatorType also in mingo/core. The values defined include;

ACCUMULATOR
EXPRESSION
PIPELINE
PROJECTION
QUERY

Lastly, the function argument to addOperators(operatorType, fn) now accepts an object with the these two internal functions;

computeValue(obj: AnyVal, expr: AnyVal, operator: string, options?: ComputeOptions): AnyVal
resolve(obj: AnyVal, selector: string, options?: ResolveOptions): AnyVal

Any extra utility may be imported directly from the specific module.

Importing submodules

Submodule imports are supported for both ES6 and ES5.

The following two examples are equivalent.

ES6

This work natively in typescript since it knows how to load commonJS modules as ES6. You may optionally install the esm module to use this syntax.

import { $unwind } from 'mingo/operators/pipeline'

ES5

Unlike the ES6 version, it is necessary to specify the operator module in the path to avoid loading any extras

const $unwind = require('mingo/operators/pipeline/unwind').$unwind

Configuration

To support tree-shaking, you may import and register specific operators that will be used in your application.

import { useOperators, OperatorType } from 'mingo/core'
import { $trunc } from 'mingo/operators/expression'
import { $bucket } from 'mingo/operators/pipeline'

useOperators(OperatorType.EXPRESSION, { $trunc, $floor })
useOperators(OperatorType.PIPELINE, { $bucket })

Using query object to test objects

import { Query } from 'mingo'

// create a query with criteria
// find all grades for homework with score >= 50
let query = new Query({
  type: "homework",
  score: { $gte: 50 }
});

// test if an object matches query
query.test(doc)

Searching and Filtering

import { Query } from 'mingo'

// input is either an Array or any iterable source (i.e Object{next:Function}) including ES6 generators.
let criteria = { score: { $gt: 10 } }

let query = new Query(criteria)

// filter collection with find()
let cursor = query.find(collection)

// alternatively use shorthand
// cursor = mingo.find(collection, criteria)

// sort, skip and limit by chaining
cursor.sort({student_id: 1, score: -1})
  .skip(100)
  .limit(100)

// count matches. exhausts cursor
cursor.count()

// classic cursor iterator (old school)
while (cursor.hasNext()) {
  console.log(cursor.next())
}

// ES6 iterators (new cool)
for (let value of cursor) {
  console.log(value)
}

// all() to retrieve matched objects. exhausts cursor
cursor.all()

Using $jsonSchema operator

To use the $jsonSchema operator, you must register your own JsonSchemaValidator in the options. No default implementation is provided out of the box so users can use a library with their preferred schema format.

The example below uses Ajv to implement schema validation.

import { RawObject } from "mingo/types"
import { JsonSchemaValidator } from "mingo/core"
import Ajv, { Schema } from "ajv"

const jsonSchemaValidator: JsonSchemaValidator = (s: RawObject) => {
  const ajv = new Ajv();
  const v = ajv.compile(s as Schema);
  return (o: RawObject) => (v(o) ? true : false);
};

const schema = {
  type: "object",
  required: ["item", "qty", "instock"],
  properties: {
    item: { type: "string" },
    qty: { type: "integer" },
    size: {
      type: "object",
      required: ["uom"],
      properties: {
        uom: { type: "string" },
        h: { type: "number" },
        w: { type: "number" },
      },
    },
    instock: { type: "boolean" },
  },
};

// queries documents using schema validation
find(docs, { $jsonSchema: schema }, {}, { jsonSchemaValidator }).all();

Note: An error is thrown when the $jsonSchema operator is used without a the jsonSchemaValidator configured.

Aggregation Pipeline

import { Aggregator } from 'mingo/aggregator'
import { useOperators, OperatorType } from 'mingo/core'
import { $match, $group } from 'mingo/operators/pipeline'
import { $min } from 'mingo/operators/accumulator'

// ensure the required operators are preloaded prior to using them.
useOperators(OperatorType.PIPELINE, { $match, $group })
useOperators(OperatorType.ACCUMULATOR, { $min })

let agg = new Aggregator([
  {'$match': { "type": "homework"}},
  {'$group': {'_id':'$student_id', 'score':{$min:'$score'}}},
  {'$sort': {'_id': 1, 'score': 1}}
])

// return an iterator for streaming results
let stream = agg.stream(collection)

// return all results. same as `stream.all()`
let result = agg.run(collection)

Benefits

Better alternative to writing custom code for transforming collection of objects
Quick validation of MongoDB queries without the need for a database
MongoDB query language is among the best in the market and is well documented

Contributing

Squash changes into one commit
Run npm test to build and execute unit tests
Submit pull request

License

MIT

weiqigod / mingo