How to save multiple objectIds Swift

Hello Backendless,
I have two tables (Users and Requests tables ).
The user can make a request with specific query and the app will check for users who match the query search. I have a column in Requests table called recipientId to save objectId of found users.

Since arrays are not supported, what is the best simple approach to save multiple objectIds of found users in order to send them the request?
I also have another question, can I use subscribe/publish messages to receive and send the requests ?

Hi Jane,

You may add them as related objects to some entity and then save a parent entity.