Querio: Condition-based query parser

Note: This is not a URL query string parser. For that, try qs.

This README is not finished and may contain some inaccuracies. Look through the test code if you'd like to see how to use and not to use Querio.

Usage

Parse specifications

To use Querio, you must first create a parse specification. These specifications dictate how Querio should parse the query strings.

A parse specification is essentially a key-value pair of strings (condition type) to condition specifications. Consider the following (it's "inspired" by repository issues):

import { values } from "querio";

const spec = {
    author: values.string,
    issue: values.int
};

This specification would tell Querio that the condition type author is to be interpreted as a string. values.string is just a predefined condition specification for strings. You can have as many condition types as you want, as long as their names don't conflict.

Given this specification, you would parse query strings using the parse function:

import { parse } from "querio";

// OK: The username must be equal to "tecc"
parse("author:tecc", spec);

// OK: The username must be equal to "tecc", and the issue ID has to be equal to 123
parse("author:tecc issue:123", spec);

// ERROR: NotANumber isn't a valid integer, so this will throw.
parse("author:tecc issue:NotANumber", spec);

// ERROR: name isn't a known condition type, so this will throw.
parse("name:tecc", spec);

Condition types

As previously mentioned, a parse specification consists of multiple condition types. These condition types consist of the type's name, and its specification.

You can have as many condition types as you want, as long as none of them have conflicting names. There is also one restriction on what names you can use for the parse specification: you cannot use the names and, or, and not.

If the example from the previous section were to be expanded, it would look something like this:

const spec = {
    author: {
        parse: (input) => input,
        compare: /* omitted for brevity */
    },
    issue: {
        parse: (input) => parseInt(input),
        compare: /* also omitted */
    }
};

A condition specification specifies how Querio should handle each condition type. They are structured like so:

type ValueType = /* Something */;
const conditionSpecification = {
    parse: (input: string): ValueType => {
        // This function parses the input string to its value type.
    }
}

Condition specifications can also be "empty", meaning they do not have a value. In this case, they act like flags.

Complex conditions

The already-provided functionality is fine and all, but what if you want more complex queries? What if you want any issue that was authored by tecc or has the ID 123? What about those not authored by johndoe? Well, Querio supports this out-of-the-box.

Addressing the first problem, using the | character between two or more conditions. For example, author:tecc | issue:123 would be interpreted as "the author must equal tecc OR the issue ID must equal 123".

The second problem can be solved by prefixing any condition with a - sign: -author:johndoe.

Another very powerful feature are groups: by encasing conditions in parentheses, that group is treated as "one condition". For example, ( author:tecc issue:123 ) | author:johndoe would be interpreted as "( the author must equal tecc AND the ID must equal 123 ) OR the author must equal johndoe".

Groups can also be prefixed with a - to negate them: -( author:tecc issue:123 ).

Explanation

Well, I needed something that could parse a string into some format well-suited for converting directly to database queries. Querio was made to fill that purpose in a generic way.

The primary inspiration in its initial design phase was the arg package.