01_FirstVersion.swift

private func joinQuery<T: Entity & SoftDeletable, U: Entity>(for entity: T.Type, joined: U.Type) throws -> Query<T> {
	return try entity
		.makeQuery()
		.withSoftDeleted()
		.join(Pivot<U, T>.self)
		.join(Join(kind: .inner, base: Pivot<U, T>.self, joined: U.self, baseKey: Pivot<U, T>.leftIdKey, joinedKey: U.idKey))
}

02_Refactored.swift

extension QueryRepresentable where Self: ExecutorRepresentable {
	public func join<Joined: Entity, Over: Entity>(
		kind: Join.Kind = .inner,
		_ joined: Joined.Type,
		over: Over.Type,
		baseKey: String = E.idKey,
		leftPivotKey: String = E.foreignIdKey,
		rightPivotKey: String = Joined.foreignIdKey,
		joinedKey: String = Joined.idKey
	) throws -> Query<Self.E> {
		let leftJoin = Join(
			kind: kind,
			base: E.self,
			joined: Pivot<Joined, E>.self,
			baseKey: baseKey,
			joinedKey: leftPivotKey
		)
		let rightJoin = Join(
			kind: kind,
			base: Pivot<Joined, E>.self,
			joined: Joined.self,
			baseKey: rightPivotKey,
			joinedKey: joinedKey
		)

		return try self.join(leftJoin).join(rightJoin)
	}
}

03_Call.swift

let textArticles = try TextArticle
	.makeQuery()
	.join(Environment.self, over: Pivot<TextArticle, Environment>.self)