CSV Export

Every resource ships with a streamed CSV export, disabled by default. It is not an action — it streams a file and opens in a new tab — so it is enabled through the policy rather than declared with action :export_csv. The route (GET /<resources>/export_csv) is auto-mounted on every resource; a split "Export" button appears on the index page once the policy permits it.

Enabling

Override one policy method:

class PostPolicy < ResourcePolicy
  def export_csv? = true   # or `index?` to mirror list access
end

export_csv? defaults to false, so export is strictly opt-in. While it returns false the button is hidden and the route returns 403.

The two exports

The control is a split button with two behaviours:

	Source	Filename
Export (primary)	The current view — selected scope + filters + search (the index's ?q), all matching rows (not just the visible page)	posts_<date>.csv
Export all (dropdown)	The entire authorized scope — ignores scope, filters, search, and default scope	posts_all_<date>.csv

"Export all" always exports everything the user is authorized to read, regardless of the current scope/filters.

Both stream via find_each, so memory stays flat regardless of row count. find_each iterates in primary-key order, so the file does not preserve the index's current sort (filters/search/scope still apply to the primary export).

Columns

The exported columns come from permitted_attributes_for_export on the policy (defaults to permitted_attributes_for_index), with the primary key always prepended as the first column.

class PostPolicy < ResourcePolicy
  def export_csv? = true
  def permitted_attributes_for_export = [:title, :author, :total, :created_at]
end

The method is named _export (not _export_csv) on purpose, so a future export format could reuse the same column set.

Customizing a field's output

The export definition DSL parallels display and column. The block receives the record and returns the cell value; label: overrides the header (default: the humanized attribute name).

class PostDefinition < ResourceDefinition
  export :author, label: "Author email", &->(post) { post.author.email }
  export :total,                          &->(post) { post.total.format }
end

The column set still comes from permitted_attributes_for_export; export only customizes how a listed column is rendered.

Value resolution

For a column without an export block, the value is read straight off the record (record.public_send(name)):

• Scalars (strings, numbers, booleans, dates) are written as-is.
• Associations render as their display label — the same display_name_of the index uses (e.g. User #5, or the record's to_label/name/title if defined) — never #<User:0x…>. Add an export block to export a specific field instead (e.g. the email).
• A name that is neither an export block nor a real method on the record renders the placeholder <<invalid column>> rather than aborting the (already-streaming) download. To export a computed or virtual column, give it an export block — a label:-only export does not supply a value, so it too renders the placeholder.

Notes & limits

• Exports run synchronously and hold the request (and a DB connection) while streaming. A background job that emails a download link is intentionally out of scope for now.
• The export button opens in a new tab (target="_blank"), which also keeps Turbo from intercepting the streamed download.
• CSV/formula injection is neutralized: any cell whose value begins with =, +, -, @, or a leading tab/CR is prefixed with a single quote so spreadsheet apps import it as literal text instead of executing it as a formula.
• csv is a runtime dependency of Plutonium (it is no longer a Ruby default gem on 3.4+).