json-query-matcher

Evaluates a mongodb-style query

Why?

I'm working on an app in which I often have arrays of objects in memory and I want to perform some operations on a subset of these arrays.

The criteria used to select these subsets can vary greatly depending on the use cases, and I want to let the users specify these criteria in a config file that will be loaded and evaluated at runtime.

I chose to have the users specify their criteria in a JSON object very strongly inspired by the syntax used to build queries in MongoDB: https://docs.mongodb.com/manual/tutorial/query-documents/

And now I'm writing this library to evaluate an object against these criteria.

Installation

npm install --save json-query-matcher

Usage

const { evaluateMatch } = require('json-query-matcher');

const items = [
    { firstName: "Gaël", lastName: "Haméon" },
    { firstName: "Gaël", lastName: "Monfils" },
    { firstName: "Alix", lastName: "Haméon" }
]

let query, result;

query = { "firstName": "Gaël" };
result = items.filter(item => evaluateMatch(item, query));
// expect(result).to.eql([{ firstName: "Gaël", lastName: "Haméon" }, { firstName: "Gaël", lastName: "Monfils" }]);

query = { "lastName": "Haméon" };
result = items.filter(item => evaluateMatch(item, query));
// expect(result).to.eql([{ firstName: "Gaël", lastName: "Haméon" }, { firstName: "Alix", lastName: "Haméon" }]);

query = { "firstName": "Gaël", "lastName": "Haméon" };
result = items.filter(item => evaluateMatch(item, query));
// expect(result).to.eql([{ firstName: "Gaël", lastName: "Haméon" }]);

query = { "$or": [{ "firstName": "Alix" }, { "lastName": "Monfils" }] };
result = items.filter(item => evaluateMatch(item, query));
// expect(result).to.eql([{ firstName: "Gaël", lastName: "Monfils" }, { firstName: "Alix", lastName: "Haméon" }]);

query = { "firstName": { "$ne": "Gaël" } };
result = items.filter(item => evaluateMatch(item, query));
// expect(result).to.eql([{ firstName: "Alix", lastName: "Haméon" }]);

Features

Operators

Comparison operators

These 8 comparison operators are available and are meant to behave the same way as in MongoDB

• $eq: equal
• $ne: not equal
• $gt: greater than
• $gte: greater than or equal
• $lt: less than
• $lte: less than or equal
• $in: in
• $nin: not in

Logical operators

These 4 logical operators are available and are meant to behave the same way as in MongoDB

• $or
• $and
• $nor
• $not

Array operators

MongoDB has 3 array operators:

• $elemMatch
• $all
• $size

As of now, only the $elemMatch operator is implemented. See the Arrays section below.

Other operators

I plan on adding operators as I need them. Up next are probably the missing array operators

Arrays

Simple queries on arrays of values

When the property that is targeted by a query is an array, the query will be considered valid as soon as one of the objects in the array matches it.

const item = {
  firstName: "Gaël",
  lastName: "Haméon",
  nickNames: ["Gaga", "Galinou"],
};

const query1 = { nickNames: "Gaga" };
const result1 = evaluateMatch(item, query1);
expect(result1).to.eql(true);

const query2 = { nickNames: { $in: ["Galinou", "Alixou"] } };
const result2 = evaluateMatch(item, query2);
expect(result2).to.eql(true);

Compound queries on arrays of objects - use of $elemMatch operator

If the targeted array contains objects and the query is compound, the query will be considered valid as soon as each part of the query, taken separately, is valid for at least one of the objects in the array.

const item = {
  firstName: "Gaël",
  lastName: "Haméon",
  pets: [
    {
      name: "César",
      species: "Dog"
    },
    {
      name: "Capsule",
      species: "Cat"
    }
  ]
};

const query1 = { pets: {"name": "César", "species": "Cat"} };
const result1 = evaluateMatch(item, query1);
expect(result1).to.eql(true);

In the example above, the query could be translated as "Check if among the pets of this person, at least one is named César, and at least one is a Cat".

If you want to check if the person has a Cat named César, you have to use the $elemMatch operator:

const item = {
  firstName: "Gaël",
  lastName: "Haméon",
  pets: [
    {
      name: "César",
      species: "Dog"
    },
    {
      name: "Capsule",
      species: "Cat"
    }
  ]
};

const query1 = { pets: { $elemMatch: {"name": "César", "species": "Cat"} } };
const result1 = evaluateMatch(item, query1);
expect(result1).to.eql(false);

Dot notation

Like in MongoDB, you can use the dot notation to access deeper properties in an object.

If we have the object below:

{
    "trip": {
        "trpNumber": "123456",
        "trpType": "1",
        "tripPoints": [
            {
                "trpptPlace": {
                    "code": "CJV",
                    "name": "Cergy-le-Haut"
                },
                "trpptArrivalTime": "09:35:15",
                "trpptDepartureTime": "09:35:50"
            },
            {
                "trpptPlace": {
                    "code": "CJP",
                    "name": "Cergy-Préfecture"
                },
                "trpptArrivalTime": "09:40:00",
                "trpptDepartureTime": "09:40:50"
            }
        ]
    },
    "block": {}
}

You can write trip.tripPoints.1.trpptPlace.name to get to "Cergy-Préfecture".