How to filter a nested relationship with Vapor Fluent

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1

I have a relationship that is structured like:

Book {
   id: UUID
   author: Author
}

Author {
   id: UUID
   genre: Genre
}

Genre {
   id: UUID
   name: String
}

I want to be able to query for books that have authors that have a specialize in a specific genre.

I want to do something like:

let query = Book.query(on: db)
    .with(\.$author) { author in
        author.with(\Author.$genre)
    }
    .filter(\Book.$author.$genre.$name, .equal, "Mystery")

But I am getting issues with accessing the genre field from the author.

If I change it to:

.filter(\Book.author.$genre.$name, .equal, "Mystery")

I get an error where it says author wasn't eager loaded.

2

If you want to do this with Fluent you need to use a join instead to bridge the tables. The other option is to do the filtering in Swift but that isn't as efficient

3

Can you provide an example of how to do this using joins, I can seem to figure it out.

Author {
id: UUID
genre: Genre
name: String
books: [Book]
}

Book {
id: UUID
author: Author
published: Date
}

How would one query for all authors with name = 'XXX' AND all books published after 'YYYY' ?

I can figure out how you filter both authors and books.

4

What have you tried?

The docs for joins are here Vapor: Fluent → Query