# AshMoney Usage Rules AshMoney provides `AshMoney.Types.Money` (aliased as `:money` if configured), backed by `ex_money`. ## Type Usage ```elixir attribute :balance, :money attribute :balance, AshMoney.Types.Money ``` ### Constraints - `storage_type` — `:money_with_currency` (default, requires `ex_money_sql` for Postgres) or `:map` - `min` / `max` — decimal bounds on the amount - `ex_money_opts` — keyword list passed to `Money.new/3` ```elixir attribute :charge, :money do constraints min: Decimal.new("0"), max: Decimal.new("1000") end ``` ## Constructing Values ```elixir Money.new(:USD, "100.00") Money.new!("EUR", Decimal.new("50")) ``` In expressions (composite type): ```elixir composite_type(%{currency: "USD", amount: Decimal.new("0")}, :money) ``` ## Expressions and Operator Overloads Supported in Ash expressions (runtime and Postgres when the extension is installed): - `+` — add two `Money` values - `-` — subtract two `Money` values; unary negation - `*` — multiply `Money` by a `decimal` - `<`, `<=`, `>`, `>=` — compare two `Money` values, or `Money` against a `decimal` Currency mismatches raise errors. All arithmetic requires matching currencies. ## AshPostgres With `AshMoney.AshPostgresExtension` installed, money operations push down to SQL. Access composite fields in expressions via: ```elixir filter expr(balance[:currency_code] == "USD") ``` Aggregates work naturally: ```elixir sum :total, :line_items, :amount ```