Is There a Way to Fetch a Type Attribute in An Ecto Query

Question

I have an Ecto Schema with payments containing an amount field. That field's type is the Money.Ecto.Composite.Type from the ex_money package(v. 5.12.3). The query is:

query =
      from(
        payment in Payment,
        where: payment.amount.currency_code() == ^currency
      )

This raises:

** (Ecto.Query.CompileError) cannot fetch field `currency_code` from `payment.amount`. Can only fetch fields from:

  * sources, such as `p` in `from p in Post`
  * named bindings, such as `as(:post)` in `from Post, as: :post`
  * parent named bindings, such as `parent_as(:post)` in a subquery

Is there a way to access the attribute and not have Ecto search for a field ?

Answer 1

This should work:

currency = "USD" # atom doesn't work

query =
  from(
    p in Payment,
    where: fragment("(?).amount.currency_code = ?", p, ^currency)
  )

Note that currency must be a string but of course you can always use to_string if you have an atom.

The reason this works is because it uses the Postgres syntax for accessing composite types.