How to execute a request with join in Room and collect everything in POJO?

Question

Java

How to execute a request with join in Room and collect everything in POJO? Tables: Message(chat_id, message_id, user_id, date), Attachment(id, chat_id, message_id, url, type)
Message has a composite key: chat_id, message_id.
It is necessary to collect POJO MessageJSON from the database (
chat_id: Int
message_id: Int
user_id: Int
attachments: ArrayList
)

Answer 1

Make a selection and as a result you can create your own object with the necessary keys:
Help 1
Help 2