我如何在 codeigniter sql 中实现以下条件？

Question

I have a table with the name message_system.

and structure of the table is as follow:

    message_system => message_id(primary key)->sender_id->receiver_id->
               message->time(current time stamp)

lets consider a $user_id = 1 and I want to select the row from the table something like

select * from message_system where sender_id = $user_id or receiver_id = $user_id  

and from the yielded result I want select only single result which has recently stored according to time stamp.

actually I want to select recent message from the message thread between two user..

edit 1:

I want to get recent message from the table with respect to each unique pair of (user1_id and user2_id). Either it is(user1_id, user2_id) or (user2_id, user1_id) usually user id of logged in user would be on of the id and another is id of user who have been messaged to current logged in user.

edit 2:

example:

lets consider user1 is logged in and he has messaged to user2. and later messaged to user3 and user4. and those all messages are stored in the table and now i want to query such that it retrieves only recent message with user2,user3,user4 in user1 wall. not all their history

edit 3 :

query should return recent message of logged in user with user1 and recent message of logged in user user2 and user3 so on.

thank you for your time.

Answer 1

select * from message_system where sender_id = $user_id or receiver_id = $user_id

would translate in CodeIgniter in:

$this->db->where('sender_id', $user_id);
$this->db->or_where('receiver_id', $user_id);
$query = $this->db->get('message_system');
$row = $query->row();

If you want the most recent input, you could order by time , and if you know you only need one row, limit to 1:

$this->db->where('sender_id', $user_id);
$this->db->or_where('receiver_id', $user_id);
$this->db->order_by('time', 'desc');//order by time
$this->db->limit('1');//limit the query to only one row
$query = $this->db->get('message_system');
$row = $query->row();// get only first

UPDATE: The solution above works if you want to find one entry corresponding to one given user. If you want to find last entry for a given pair of users, thing would look like this if unknown who would be the sender and who would be te receiver:

$this->db->where_in('sender_id', array($user_id1, $user_id2));
$this->db->where_in('receiver_id', array($user_id1, $user_id2));
$this->db->order_by('time', 'desc');//order by time
$this->db->limit('1');//limit the query to only one row
$query = $this->db->get('message_system');
$row = $query->row();// get only first

And like this if you know exactly who is who:

$this->db->where('sender_id', $user_id1);
$this->db->where('receiver_id', $user_id2);
$this->db->order_by('time', 'desc');//order by time
$this->db->limit('1');//limit the query to only one row
$query = $this->db->get('message_system');
$row = $query->row();// get only first

Answer 2

With little bit modification of the table I have come up with an idea.

earlier my table structure was:

message_system => message_id(primary key)->sender_id->receiver_id->
               message->time(current time stamp)

after modification:

message_system => message_id(primary key)->sender_id->receiver_id->
               message->time(current time stamp)->unique_pair_key

unique_pair_key is to identify the message between two user uniquely and value would be something like this ($sender_id^2 + $receiver_id^2) which is unique for given pair.

all messages between two particular user would be identify by this unique_pair_key.

so taking logged_in user as the reference, with respect to him only recent message with different user (if there any) should be shown (similar to stack overflow recent inbox message )and on clicking that particular message it should direct to their message thread.

model/model.php

     public function get_notification($user_id)
          {

       $this->db->where("receiver_id",$user_id);
       $this->db->where("sender_id",$user_id); 

    //because recent message would either be sent or received by logged in user

    $this->db->select_max('message_id');

   // latest message would have greatest value of id

    $this->db->group_by('unique_pair_key');
    $query = $this->db->get('message_system ');

   //returns latest message_id with unique pair in which on of  them is $userid.
}

above query only generates message id with that we can further query to get message

If you have any better solution please share with us.