[jira] [Resolved] (ARROW-15705) [JavaScript] Structs don't append nulls properly

["Dominik Moritz (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-15705?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Dominik Moritz resolved ARROW-15705.
------------------------------------
    Fix Version/s: 8.0.0
       Resolution: Fixed

Issue resolved by pull request 12451
[https://github.com/apache/arrow/pull/12451]

> [JavaScript] Structs don't append nulls properly
> ------------------------------------------------
>
>                 Key: ARROW-15705
>                 URL: https://issues.apache.org/jira/browse/ARROW-15705
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: JavaScript
>    Affects Versions: 7.0.0
>            Reporter: Alfred Mountfield
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 8.0.0
>
>          Time Spent: 6.5h
>  Remaining Estimate: 0h
>
> If you have a StructBuilder, then the `set` method (which is inherited from `Builder`) on it will modify the null-bitmap and then return directly due to this snippet:
> {code:javascript}
> public set(index: number, value: T['TValue'] | TNull) {
>         if (this.setValid(index, this.isValid(value))) {
>             this.setValue(index, value);
>         }
>         return this;
>     }
> {code}
>  
> I believe this breaks the spec, as it results in the children arrays not having their lengths and null-counts increased. (At least the Rust implementation expects child arrays to be the same length as their parent struct array, and the spec seems to imply that's a requirement)
> I think there's an easy fix which would be to call `this.setValue` for `StructBuilder`s regardless of `this.isValid(value)`
> Related to https://issues.apache.org/jira/browse/ARROW-15651



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