date(<link>) queries

[ontrou]

I have seen #173 and #561, but I can't see how to use wiki link dates in practice. For example:

# Project 1
---
completed: 2019-10-31
---

# Project 2
---
completed: [[2019-10-31]]
---

This dataview query picks up Project 1 but not Project 2:

LIST 
WHERE completed <= date(2019-12-31) and completed >= date(2019-01-01)

This dataview query picks up neither project, not even Project 2:

LIST 
WHERE completed <= date([[2019-12-31]]) and completed >= date([[2019-01-01]])

My questions:

1. How do I manipulate wiki link dates?
2. For the long-term best practices, which is better and more flexible, to wiki link dates or say no to wiki link dates?

[blacksmithgu]

You need to use date on the link as welt:

LIST 
WHERE date(completed) <= date(2019-12-31) and date(completed) >= date(2019-01-01)

Link-date comparisons don't work by default, but using date on a link will convert it into a date, which then can be compared.

[ontrou]

Thank you so much blacksmithgu. That clears up a bunch of my confusion.

The Reference (an aside: big thank-you @tzhou for the search bar!) says date(any) parses from a string, date, or link object. What is an example of a string? I tried various date formats, but they didn't pick up anything.

[blacksmithgu]

Dataview parses YYYY-MM-DD ISO dates currently; support for plain-text dates like "November 10th 2021" is in the works but not available yet. So

date("2021-08-13")
date("1997-01-01")

and such does currently work.