Mysql – Messaging Database – How to handle multiple recipients

database-designMySQL

So I am trying to develop a relational database (I'm using MySQL, planning on a Java front end) where I have 3 tables (People, where I store names and relevant personal information… and Messages (where for every message sent, the relevant information is stored. Each message is given an ID# from which you can draw the date and time sent, the content of the message, the sender of the message, and the recipient of the message).

My problem is setting up the database such that each message can have just one sender but multiple recipients. For instance, I can easily handle message ID 73 being sent from User 6 to User 3. But how would I handle if message ID 74 was sent from user 4 to users 2,3, and 8? Is there a way to allow multiple recipients? Would I need to rethink how the database is structured? Anyone got some advice/tips?

Best Answer

You need to have a many-to-many table for your message recipients. Think about it this way, each message can be sent to one or more recipients. Also, each recipient can presumably receive zero, one or more messages. This means you have a many-to-many and you need an intersection table to record this information in your database.

Consider this ERD:

ERD

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Groups, Users, and Inbox

Here's how I think I would approach the issue:

TABLE message
    id number,
    message varchar2(8000),
    sent_by_user number,
    etc...

TABLE inbox
    id number,
    user_id number,
    message_id number,
    etc...

Then, when sending to a group, I would go ahead and add an entry to each user's inbox with a pointer at the message. This way you aren't duplicating the message content, but you simplify the system by allowing users to perform their own actions on group messages without affecting the group message for the group as a whole.

Not sure it is a complete answer to your issue, but I would go this route since it means that message management is always a user-level issue; only during send operations do groups need to enter the equation.

Mysql – What relationship type to use for this messaging system

Assuming you're not trying to keep track of threads of messages, I.E. you send a message to N people, and they can't reply:

1) user needs no references to other tables
2) a message should have an ID (obviously) and a reference to the user who sent it originally
3) you need a table that connects a single message and its recipients (users) that looks like this: message_recipients{user_id, message_id} where the primary key is the combination of the two fields. This ensures that one message can have many recipients, and that users can be the recipients of many different messages.

One user can send a message to one or many users

This is accomplished via the message_recipients table

Messages can be sent only to registered users (i.e. to an existing 'idUser' record)

You'll need to handle this in your application logic as well, but if you add (as you should) a foreign key and (depending on your DBMS) a NOT NULL restriction on each of the columns in message_recipients table, it will be possible to create a record in message_recipients without the recipient existing.

There should be tracking of sent messages (who sent the message and to whom)

This data model supports that. Example:

Find the name of all recipients of messages sent by user Mike Johnson

(edited to give better aliases to the two different uses of the user table)

SELECT recipient.firstname, recipient.lastname
FROM user recipient
JOIN message_recipient mr ON recipient.id = mr.user_id
JOIN message m ON m.id = mr.message_id
JOIN user sender ON m.user_id = sender.id
WHERE sender.firstname = 'Mike' and sender.lastname = 'Johnson'

Best Answer

Related Solutions

Groups, Users, and Inbox

Mysql – What relationship type to use for this messaging system

Find the name of all recipients of messages sent by user Mike Johnson

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