ash_postgres/documentation/how_to/using-fragments.md

Using Fragments

Fragments allow you to use arbitrary postgres expressions in your queries. Fragments can often be an escape hatch to allow you to do things that don't have something officially supported with Ash.

Examples

Use simple expressions

fragment("? / ?", points, count)

Call functions

fragment("repeat('hello', 4)")

Use entire queries

fragment("points > (SELECT SUM(points) FROM games WHERE user_id = ? AND id != ?)", user_id, id)

Using entire queries like the above is a last resort, but can often help us avoid having to add extra structure unnecessarily.

sql function in a calculate

calculations do
  calculate :lower_name, :string, expr(
    fragment("LOWER(?)", name)
  )
end

sql function in a migration

create table(:managers, primary_key: false) do
  add :id, :uuid, null: false, default: fragment("UUID_GENERATE_V4()"), primary_key: true
end