MongoDB - PHP手册参考方法适用性

Question

MongoDB newbie here. I'm having the first approach on references, and my main doubt is if i'am using the appropriate strategy(manual references) for my situation.

Working on 2 collections(user, message) in the same db, lets make an example of a document stored in user collection:

array (
  '_id' => new MongoId("5231817277758e660c7202c4"),
  'uname' => 'pluto',
  'pwd' => new MongoInt32(1234567),
  'email' => '[e-mail]',
  'phone_home' => new MongoInt64(23409238),
  'phone_work' => new MongoInt64(54389724),
  'phone_mobile' => new MongoInt64(9823422),
  'visible' => new MongoInt32(1),
)

and an example of a document stored in message collection (sent FROM an other user TO the user above 'pluto'):

array (
  '_id' => new MongoId("524358102660b2c70b8b4567"),
  'from_uid' => '5231817277758e660c7202d7',
  'to_uid' => '5231817277758e660c7202c4',
  'object' => 'mongo manual Ref',
  'content' => 'is that the correct approach?',
  'datetime' => '2013-09-25 23:39:28',
)

The user logged in ('pluto') can see all the messages he received from other users but, i don't wat to print the 'from_uid' value, i want to replace it with the username of the sender.

My main doubt is if manual references is the right approach for this scenario, because with this technique(if i havn't miss understood everything), print a list of message would involve:

1. the 'query' for print the list of messages
2. an other 'query' for retrieve the username from the other collection, for each messages. Also if a user have received 1000 messages, this approach will have to run 1001 query??

My secondary doubt is if there is a way for directly merge or replace the result of two cursors

Answer 1

Given your use case it would probably be ok to duplicate a little bit of data and store some of the necessary fields about the sending user as an embedded document - in this case, the username.

array (
  '_id' => new MongoId("524358102660b2c70b8b4567"),
  'from_user' => array(
     'uid'   => '5231817277758e660c7202d7',
     'uname' => 'mars'
   ),
  'to_uid'   => '5231817277758e660c7202c4',
  'object'   => 'mongo manual Ref',
  'content'  => 'is that the correct approach?',
  'datetime' => '2013-09-25 23:39:28',
)

This approach means that when you query for messages to a user ( in which you already know the to_uid), you get all of the messages with the correct id to the from_user, but also already have their username to display.

Now, instead of querying 1000+ times, you only need to query when there is more information needed about a user - such as fetching their profile, etc...