HasOneThroughAssociation

For example, if each book belongs to a library, and each library has one address, then one knows where the book should be returned to:

struct Address: TableRecord { }

struct Library: TableRecord {
    static let address = hasOne(Address.self)
}

struct Book: TableRecord {
    static let library = belongsTo(Library.self)
    static let returnAddress = hasOne(Address.self,
                                      through: library,
                                      using: Library.address,
                                      key: "returnAddress")
}

As in the example above, HasOneThroughAssociation is always built from two other associations. Those associations can be any association that declares a to-one connection (AssociationToOne).