# `MishkaCmsCore.Runtime.Resources.Changes.SetLanguageGroupId`
[🔗](https://github.com/mishka-group/mishka_cms_core/blob/v0.0.1/lib/mishka_cms_core/runtime/resources/__changes/set_language_group_id.ex#L5)

Automatically sets language_group_id for master collections.

This change handles the multilingual collection structure by setting the language_group_id
to the record's own ID for master collections (collections without a language_group_id).
This creates a self-referential relationship where master collections point to themselves,
while translations point to their master collection's ID.

## Behavior

- **Master collections**: When `language_group_id` is nil during creation, the change
  automatically sets it to the record's own ID after insertion using an after_action hook.

- **Translation collections**: When `language_group_id` is explicitly provided (pointing
  to a master collection), the changeset passes through unchanged.

## Implementation Details

The change uses `after_action` to perform the update because we need the record's ID
first (generated during insertion). The update:
- Uses the record's site_id as the tenant context
- Bypasses authorization (internal system operation)
- Updates only the language_group_id field

## Usage

    create :create do
      change MishkaCmsCore.Runtime.Resources.Changes.SetLanguageGroupId
    end

## In the same write

Pass `before_action?: true` and the group is written WITH the row instead of by a second write
after it:

    create :create do
      change {MishkaCmsCore.Runtime.Resources.Changes.SetLanguageGroupId, before_action?: true}
    end

    update :update do
      change {MishkaCmsCore.Runtime.Resources.Changes.SetLanguageGroupId, before_action?: true}
    end

The id is already on a create's changeset by the time a before-action runs, so nothing waits for
the insert. `MishkaCmsCore.Runtime.Page` needs this: its `:update` validates and signs code,
versions the page, broadcasts it and queues a compile, so the second write turned one save into
two versions, two broadcasts and two compile jobs.

On an update the same rule keeps a group from being emptied — a record whose group is set to nil
becomes the master of a group of its own rather than a record with no group at all.

On a restore it gives a group to a record archived before it had one. A
`prevent_archived_*_updates` trigger refuses every other write to an archived row, so the
restoring write is the first one that can:

    update :unarchive do
      change set_attribute(:archived_at, nil)
      change {MishkaCmsCore.Runtime.Resources.Changes.SetLanguageGroupId, before_action?: true}
    end

## Example Flow

### Creating a master collection (English):
```elixir
# User provides: language_group_id = nil
Ash.create(Collection, %{name: "Tech", language: "en", ...}, tenant: site_id)
# After insert: language_group_id automatically set to record.id
# Result: id = "abc123", language_group_id = "abc123"
```

### Creating a translation (Persian):
```elixir
# User provides: language_group_id = "abc123" (master's ID)
Ash.create(Collection, %{name: "فناوری", language: "fa", language_group_id: "abc123", ...})
# After insert: language_group_id remains "abc123"
# Result: id = "def456", language_group_id = "abc123"
```

## Database Implications

This creates a structure where:
- Master collections: `id == language_group_id`
- Translations: `language_group_id == master_collection.id`
- Query all variants: `WHERE language_group_id = X` (includes master and all translations)

# `change`

Applies the language_group_id assignment logic.

## Parameters
- `changeset` - The Ash changeset for the collection being created
- `opts` - `before_action?: true` writes the group with the row (see "In the same write")
- `_context` - Change context (unused)

## Returns
Modified changeset with a hook that sets the group if language_group_id is nil,
otherwise returns changeset unchanged

---

*Consult [api-reference.md](api-reference.md) for complete listing*