expression-to-mql

A node package and CLI executable to parse arithmetic expressions and convert them to MongoDB aggregation expressions.

Features

The expression language allows the following:

• Field names (unquoted, or quoted with single or double quotes)
• Reference to nested fields using dot notation: product.quantity
• Literal numbers (integer or decimal)
• Operators: +, -, *, /
• Brackets for grouping (, )
• Whitespace outside of quoted strings is irrelevant

Examples of valid expressions:

• price * quantity
• 'total amount' * 1.1
• (foo.temp - 32)*5/9

The expressions are converted to valid MongoDB Aggregation Expressions to be used in $project or $addFields stages.

CLI usage

While the intended use is programmatic via ES6 modules or CommonJS require, it also comes with a tiny executable so that it can easily be used at the command line. To use this tool from the command line, follow these steps:

1. npm install -g expression-to-mql
2. expr2mql 'foo + 1'

Alternatively, you can check out the repository locally and run:

node ./bin/expr2mql.js 'foo + 1'

API usage

The main function is exprToMQL(), which can be used as follows:

import exprToMQL from 'expression-to-mql';

const mql = exprToMQL('foo + 1');
console.log( JSON.stringify(mql) );

This would output

{"$sum":["$foo",1]}