zeus
48 lines
1.7 KiB
Swift
48 lines
1.7 KiB
Swift
/// The `HasOneThroughAssociation` sets up a one-to-one connection with
|
|
/// another record. This association indicates that the declaring record can be
|
|
/// matched with one instance of another record by proceeding through a third
|
|
/// record.
|
|
///
|
|
/// 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:
|
|
///
|
|
/// ```swift
|
|
/// 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``).
|
|
public struct HasOneThroughAssociation<Origin, Destination> {
|
|
public var _sqlAssociation: _SQLAssociation
|
|
|
|
init<Pivot, Target>(
|
|
through pivot: Pivot,
|
|
using target: Target)
|
|
where Pivot: AssociationToOne,
|
|
Target: AssociationToOne,
|
|
Pivot.OriginRowDecoder == Origin,
|
|
Pivot.RowDecoder == Target.OriginRowDecoder,
|
|
Target.RowDecoder == Destination
|
|
{
|
|
_sqlAssociation = target._sqlAssociation.through(pivot._sqlAssociation)
|
|
}
|
|
}
|
|
|
|
extension HasOneThroughAssociation: AssociationToOne {
|
|
public typealias OriginRowDecoder = Origin
|
|
public typealias RowDecoder = Destination
|
|
}
|