php PDO change connection during script via function - php

Question

I have an app that has to use more than one database for reasons of client protection and archiving with a core one for administration - eg user detail storage. I appreciate the need to migrate from the mysql extension (soon to be deprecated) and I first tried mysqli but could not get away from the persistent connection, even using the change_user function, probably because the same user/pass combo is used so cross-database joins are possible.
I am implementing many stored procedures during the migration to reduce bottlenecks. MYSQL now assigns SPs to each specific database, so it is important to be connected to the right one when making a CALL. That means putting full database.table references in queries is not practical
So I have turned to PDO.
I created a test script:
$db_host="localhost";
$db_username='root';
$db_pass='';
$add='admin';
$db_name='host_base_name'.$add;
try{
$db= new PDO('mysql:host='.$db_host.';dbname='.$db_name,$db_username,$db_pass);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);
$result= $db->query("SELECT firstname from centralusers WHERE usr_id='1'");
while($row=$result->fetch(PDO::FETCH_ASSOC)){echo $row['firstname']."<br>";}
}
catch(PDOException $e){echo $e->getMessage();}
$add='test';
$db_name='host_base_name_'.$add;
try{
$db= new PDO('mysql:host='.$db_host.';dbname='.$db_name,$db_username,$db_pass);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);
$result= $db->query("SELECT stage_desc from action_stage WHERE stage_id='1'");
while($row=$result->fetch(PDO::FETCH_ASSOC)){echo $row['stage_desc']."<br>";}
}
catch(PDOException $e){echo $e->getMessage();}
And that successfully does the switch - I tried across three databases but have not shown the third for economy.
However, in the development code my script has a 'require' file which contains a function to handle the connection. it is sent the last part of the table name via the call (a process that has worked fine in the mysql extension. Here is that code;
function db_connect($add) {
$db=NULL;
$db_host="localhost";
$db_username='root';
$db_pass='';
$db_name='host_base_name_'.$add;
try{
$db= new PDO('mysql:host='.$db_host.';dbname='.$db_name,$db_username,$db_pass);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);
}
catch(PDOException $e){echo $e->getMessage();}
return $db;
}
After the second call (to change the database) my next query produces an error that the table cannot be found - and gives the 'host_base_name_ 'part of the table reference as the original. I thought the NULL call would have destroyed the instance.
If I put the $db=NULL; in the calling script, just before the function I get a "Call to a member function query() on a non-object " Scream error.
Why does one work and not the other because they seem identical and how could I work round this?

Answer 1

Have separate PDOs for each database
$db_host="localhost";
$db_username='root';
$db_pass='';
$add='admin';
$db_name1='host_base_name'.$add1;One database
$db_name2='host_base_name'.$add2;Other database
try{
//PDO for one database
$db1= new PDO('mysql:host='.$db_host.';dbname='.$db_name1,$db_username,$db_pass);
$db1->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);
//PDO for other database
$db2= new PDO('mysql:host='.$db_host.';dbname='.$db_name1,$db_username,$db_pass);
$db2->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);

Answer 2

For those coming across this in future, I found I could indeed replace the function call with a class and create a new connection to a different database. Along the way I discovered the tremendous speed improvement by replacing 'localhost' with '127.0.0.1' -halving the execution of a test script from 0.0060 seconds to 0.0029 which can be significant in complex scripts.
So here is my class - because it is included anyway at the top of the script, I put the main connection parameters at the head of the include so they could be used in the class. The $db_name is modified in the script so it refers to the correct database.
$db_host='127.0.0.1';
$db_user='root';
$db_pass='';
$db_name='host_base_name';
class databaseConnect{
public function connect($db_host, $db_user,$db_pass,$db_name){
try{
$db= new PDO('mysql:host='.$db_host.';dbname='.$db_name,$db_user,$db_pass, array(PDO::ATTR_PERSISTENT=>false));
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);
}
catch(PDOException $e){echo "Error: ".$e->getMessage()."<br />"; die(); }
return $db;
}
}
I get the new database connection instance (in this case to 'host_base_nametest' using the code below I replace $con with another variable when I have to switch databases, essentially giving me totally flexible and transportable database naming within the connection:
$add='test'; // in production this comes from another variable
$db_inst=$db_name.$add; //builds the database name
$con=new databaseConnect; //calls the class
$db=$con->connect($db_host, $db_user,$db_pass,$db_inst); //gets the new instance