Join

A virtual, read-only field that displays documents from another collection that reference the current document. No data is stored — results are computed at read time by querying the target collection.

Lua Definition

crap.fields.join({ name = "posts", collection = "posts", on = "author" })

This reads as: “Show me all documents in the posts collection where posts.author equals this document’s ID.”

Properties

Behavior

• No database column — join fields are virtual. No migration, no storage.
• Read-only — displayed in the admin UI but not editable. No form input is rendered.
• No validation — since no data is submitted, validation is skipped entirely.
• Admin UI — shows a list of linked documents with clickable links to edit each one. Displays “No related items” when empty.
• API responses — at depth >= 1, join fields return an array of document objects from the target collection. At depth = 0, join fields are omitted (no stored value).

Example

Given an authors collection and a posts collection where each post has a relationship field called author:

-- collections/authors.lua
return {
    slug = "authors",
    fields = {
        crap.fields.text({ name = "name", required = true }),
        crap.fields.join({ name = "posts", collection = "posts", on = "author" }),
    },
}

When editing an author, the “posts” join field displays all posts where posts.author equals the current author’s ID.