query.not_unique

A query that returns one record, or none, picks it by a test that several records could match.

Area 6, Reads and writes; not declinable; the next step is usually the agent's.

Why Jadpo refuses it

A result type of Book or Book? says at most one record comes back. Only a where: that tests a unique field with == can promise that. Here title isn't unique, so two books with the same title would both match, and the query would have no right answer.

What it looks like

main.jadpo:

type Title = Text {    max_length: 80}entity Book {    id: Uuid    title: Title    subtitle: Title?    available: Bool}query book_titled(title: Book.title) -> Book? {    from: Book    where: Book.title == title}

   |14 |     where: Book.title == title   |     ^^^^^ not a unique field

(agent) at the end of the next: line means your coding agent can make the fix itself.

How to fix it

If no two books should share a title, make title unique:

    title: Title {        unique: true    }

The database refuses a second book with a title already taken, so every write that sets title now needs a conflict: arm for it. book_titled gives the one book with that title, or none.

If several books may share a title, return a list, with order: and limit::

query books_titled(title: Book.title) -> List<Book> {    from: Book    where: Book.title == title    order: [Book.id asc]    limit: 20}

The query gives up to 20 books with that title, and callers handle a list rather than one book.

Related

• How many records come back
• Unique rules
• data.conflict_unmapped