Relational field conditions

[brandonkelly]

Description

This adds new condition settings to Assets, Entries, and Users fields, which can be used to further limit which elements should be relatable, beyond the field types’ existing settings.

For example, the “Selectable Entries Condition” setting on Entries fields could be used to limit the relatable entries to only those of a certain entry type:

Plugin-provided relational fields can add their own condition setting by overriding BaseRelationField::createSelectionCondition() method:

protected function createSelectionCondition(): ?ElementCondition
{
    $condition = Entry::createCondition();
    $condition->queryParams = ['section', 'sectionId'];
    return $condition;
}

Related issues

• Limit relations by entry type #8524
• Allow Entries fieldtype to configure individual EntryTypes, not full Sections #8686

[linear]

DEV-78 Relational field conditions

Relational fields should include condition builders for fine-tuning which elements should be relatable, using a condition builder for defining element query params.

(Only params that reference things in the project config can be used, since field settings are also stored in the project config.)