Php/Mysql: Database class and dependency injection -

i'm trying adopt dependency injection pattern mid-scale project have been working on. of classes interact database on level , instead of instantiating pdo object inside each class, instantiate single pdo object on controller level , inject object classes require database connection. way, classes using same connection , whole process making unit testing pretty easy.

however, things little bit complex when try use transaction these classes. our database heavily de-normalized , each action requires multiple inserts/updates different classes. give basic example, let's have classes below:

    class student{         public function addcourse($pdo,$course){             //$pdo->execute();         }     }      class course{         public function incrementstudentcount($pdo){             //$pdo->execute();         }     } 

as see, both addcourse , incrementstudentcount methods must work in single transaction mode.however,student , course classes not aware of whether transaction started or not in $pdo object. don't know if rollback required in case problem occurs.

i thought of creating pdo wrapper class , using class database interactions. way, can keep transaction state inside class. basically, looks this:

    class pdowrapper {         private $transactionstarted=false;         private $pdo;         public function __construct($pdo){             $this->pdo=$pdo;         }         public function starttransaction(){             $this->transactionstarted=true;              $this->pdo->begintransaction()         }         public function query($query){             try{                 //$this->db->execute($query);             }             catch(pdoexception e){                 if($this->transactionstarted){                     $this->db->rollback();                 }             }         }     } 

well, i'm not sure approach way go. so, suggest?

you're right in classes should not know going on in other class / db. none of matters, student , user classes concerned inserting database.

it shouldn't matter if there's transaction or not: should still doing exact same thing they'd doing regardless, inserting rows. i'd recommend have controller takes care of both tasks, so:

$pdo->starttransaction(); //however instantiate course object, here $course = new course; //same student $student = new student; $student->addcourse($pdo, $course); $course->incrementstudentcount($pdo); $pdo->commit(); 

when commit database, queries go through. can rollback in case of error so:

try {     $pdo->starttransaction();     //code } catch(pdoexception $e) {     $pdo->rollback(); }