Date handling for GQL

[ErisDS]

At the moment, there is little-to-no consideration for date handling in GQL. There are a few mentions of dates in TryGhost/Ghost#5604. In particular the post-processing section under Implementation talks about handling dates after the parser is finished.

Date-like values can realistically appear in different forms:

• A Number could also be a JavaScript timestamp
• A Literal could be a valid ISO 8601 date like 2015-07-27T14:54:21
• A String could contain a valid date in many different forms

It is very difficult to distinguish a date from another value at the lexer level, or to determine whether a String was intended to be a date or a string. The best way we have, therefore, to detect dates, is to assume that any value provided for a date-based property is a date.

That is, if the property name is created_at, updated_at, published_at, last_login or any other known dates and the value is a Number, a Literal or a String, we should try to turn the value into a date using new Date(). This provides us with a well understood set of recognised date formats, and should mean that passing dates from handlebars inside a Ghost theme will work.

E.g. {{#get "posts" filter="published_at: >'{{post.published_at}}'"}} (note the date is wrapped in single-quotes), without any date handling, will create a query in the form:

select * from "posts" where "posts"."published_at" > 'Sat Jun 27 2015 13:02:12 GMT+0100 (BST)'

And SQL doesn't know what to do with that date.

Instead we need to ensure that if we have a date that can be understood by new Date, then SQL is always passed a date in a format it understands.

We also need to ensure this works for all the supported SQL types: SQLite, MySQL and pg.

[schuer]

Just want to say I would love to see this feature coming :)
The other day I was about to set up an archives page and got stuck at bundling posts by year. Took me a while to find out it’s GQL missing the date features.

(Thx for you good work at Ghost and for spotting issues even before users run across them!)

[laran]

I implemented this here: laran@279f363

I called them 'transformers'. Basically callbacks which transform each value.

It's an extension of the work in #17. If that PR gets accepted the transformers can be merged in as well.

[kirrg001]

@ErisDS Do you want to keep this issue? Let me know, then i will move it over to NQL 🙂

[ErisDS]

We can close this. It turns out dates do basically work and we use them in Ghost.

If we decide to improve this, we can always raise a new issue with a proper spec for what we want to improve.