Make empty and nempty work for Array types

[rijkvanzanten]

Discussed in #18039

^{Originally posted by soulseekah April 3, 2023}

Summary

There is currently no way to check if an array is empty or not.

_empty does not work as per #18028

while "_eq": [] is not supported

Basic Example

Create a flow, Read step that returns [] when nothing is found, Condition that checks {"$last": {"_empty": true}} or {"$last":{"_eq": []}}. First option expects '', false or null. Second option errors out as unsupported operand.

Motivation

Checking if an array is empty or not is a quite important and foundational construct to have available in any system.

Detailed Design

_empty and _nempty should treat an empty [] as falsy, despite them being always truthy.

Requirements List

Must Have:

• _empty checks for length of 0 on array typed values
• _nempty checks for length of >= 1 on array typed values

Should Have:

n/a

Could Have:

n/a

Won't Have:

n/a

Drawbacks

There are no known drawbacks to supporting arrays in _empty and _nempty.

Alternatives

Writing a custom script that checks .length is a usable approach, before applying a condition.

Adoption Strategy

_empty will start supporting arrays. A notice will be posted on the release notes to notify people of the possible breaking change

Unresolved Questions

n/a

[shipsides-sparknel]

#15504 ([] not being considered as null for field validation) is tangentially related to this, which was attempted to be fixed but instead caused #16291. is finding a solution for this part of the scope of this?

[jekuer]

The mentioned alternative does not work well when filtering within a (for example) delete flow step, where it is about a lot of items. Of course, you can also do this via a script, but feels like unnecessarily complicated.

What you can do, right within the filter (since function parameters are now possible):

{
    "count(field)": {
        "_eq": 0
    }
}

Maybe an alternative approach for this ticket is to update documentation instead of updating "_empty"?

[MarvinXu]

The mentioned alternative does not work well when filtering within a (for example) delete flow step, where it is about a lot of items. Of course, you can also do this via a script, but feels like unnecessarily complicated.

What you can do, right within the filter (since function parameters are now possible):

{
    "count(field)": {
        "_eq": 0
    }
}

Maybe an alternative approach for this ticket is to update documentation instead of updating "_empty"?

@jekuer how did you make type check work for this?

[jekuer]

@MarvinXu , you mean before whether it's an array or not OR regarding the type of the array element?

Regarding first: This is quite static in my setup. Not sure, but most probably you could also work with the "_or" operator. like nnull = false OR count = 0. This would fail if not given at all, null or an empty array.

Regarding latter one: I don't 😆

[MarvinXu]

@jekuer sorry, I mean Typescript error

[jekuer]

Good catch. I don't, because I use this only at the integrated Flow-Feature of Directus. In my app, I am filtering out empty arrays after fetching the data from the Directus backend.