Aliases/expansions research

Background

nql-lang introduced aliases support mid of 2018. nql-lang is able to replace keys in a filter string.

State of NQL 0.2.1

A month a go we added the missing NQL features (e.g. relations, mongo json utility etc.). This is what you have to know:

Aliases are now called: expansions. We no longer use the wording aliases. The reason is that there are two requirements for replacing stuff in a filter:

1. replace a key name e.g. filter=tags:x -> {tags.slug:x}
2. expand a statement if a key name matches e.g. filter:primary_tag:de -> {$and: [{tags.slug:de}, {sort_order:0}]} (optional)

That means, the expansions feature is more than just a simple string replacement. It can expand the mongo JSON query.

When the merge json utility logic was moved over from Ghost to NQL, i noticed that we no longer use nql-lang to replace the aliases/expansions. The expansion logic does it now.

Why?

All string filters are parsed by nql-lang as first step. And afterwards we pass the parsed filters into the utility. As soon as a key matches the configured expansions, the expansion logic replaces the key in the mongo json object and adds/extends the expansion filter to the target statement

e.g.

filter=tags:bla+primary_tag:blub

should be

filter=tags.slug:bla+(tags.slug:blub+posts_tags.sort_order:0)

If nql-lang would replace the name independently of the expanded filter, we first would get:

{$and: [tags.slug:bla, tags.slug:blub]}

Now you don't know which part you need to expand?

Discussion/Research

We have not spend further time on this. Is it possible to use nql-lang again?
This needs a bit playing & thinking.

Compare the alias support introduced in the nql-lang commit with the expansion logic in mongo-utils/lib/mongo-utils.js around line 114. Trace how parsed filters and merge-json expansion interact, starting with the tags and primary_tag example. Done means determining whether nql-lang can safely handle expansions again without losing the target statement context, and documenting the conclusion.