Question

I am creating a communication module with email and onsite messaging. 4 questions:

1) When storing the messages, it can belong to folders (Spam, trash, inbox, outbox, etc). Are these separate tables or 1 table with just a column for “folder” which is FK to a “folder lookup table”?

2) Like on hotmail, a user can create x number of custom folders so how to represent that in the data model? I can say inbox = id 1, outbox = id 2, etc but for the custom folders like “vacation email”, “work email”, etc i am not sure how to show that in the Data model if a message resides in that folder.

3) One email goes to multiple people. Does this mean i need to have 1 row per user sent to?

4) Lastly, messages have attachments. i assume that means a separate attachments table which FK links to which ever table (s) are used for storing messages?

Answer 1

1&2: Folders need to be an entity, relationship MessageFolder one to many to Message

3: MessageUser entity with UserID, MessageID, Type (Sender,Recipient)

4: Seperate table for attachments (MessageAttachments).

CREATE TABLE `message`
  (
     `id`       INTEGER NOT NULL AUTO_INCREMENT,
     `author`   INTEGER NOT NULL,
     `contents` TEXT NOT NULL,
     `subject`  TEXT NOT NULL,
     PRIMARY KEY (`id`)
  );

CREATE TABLE `messagefolder`
  (
     `id`         INTEGER NOT NULL AUTO_INCREMENT,
     `id_message` INTEGER NOT NULL,
     `id_folder`  INTEGER NOT NULL,
     PRIMARY KEY (`id`)
  );

CREATE TABLE `folder`
  (
     `id`   INTEGER NOT NULL AUTO_INCREMENT,
     `name` VARCHAR(200) NOT NULL,
     PRIMARY KEY (`id`)
  );

CREATE TABLE `messageattachment`
  (
     `id`         INTEGER NOT NULL AUTO_INCREMENT,
     `fk_message` INTEGER NOT NULL,
     PRIMARY KEY (`id`)
  );

CREATE TABLE `user`
  (
     `id` INTEGER NOT NULL AUTO_INCREMENT,
     PRIMARY KEY (`id`)
  );

CREATE TABLE `messageuser`
  (
     `id`         INTEGER NOT NULL AUTO_INCREMENT,
     `fk_message` INTEGER NOT NULL,
     `type`       INTEGER NOT NULL,
     PRIMARY KEY (`id`)
  );;

ALTER TABLE `message` ADD FOREIGN KEY (author) REFERENCES `user` (`id`);
ALTER TABLE `messagefolder` ADD FOREIGN KEY (id_message) REFERENCES `message` (`id`);
ALTER TABLE `messagefolder` ADD FOREIGN KEY (id_folder) REFERENCES `folder` (`id`);
ALTER TABLE `messageattachment` ADD FOREIGN KEY (fk_message) REFERENCES `message` (`id`);
ALTER TABLE `messageuser` ADD FOREIGN KEY (fk_message) REFERENCES `message` (`id`);