what is the common practice on doing oo in db? - php

Question

Here is situation.... ...
I have a DBManager, which is implement a DBInterface, in the DBInterface, I got 4 method:
-create(DBCmd);
-read(DBCmd);
-update(DBCmd);
-delete(DBCmd);
The DBCmd object is responsible for generate the SQL statement, and the DBCmd requires an object in sql statement:
class DBCmd{
public _constructor($aObj){
}
public executeCreate(){
}
public executeRead(){
}
public executeUpdate(){
}
public executeDelete(){
}
}
The flow will be like this:
aObject ---> put it into DBCmd ----> put the DBCmd in DBManager ---> execute
But the problems happen when I get some objects related to other tables, for example...a customer have a purchase record, and which purchase record have many items....
So, what do I do in my read method? should I read all the records related to the customer?? Do I need to loop all the items inside the purchase record too?
If yes, when I doing read customer, I need to query 3 tables, but some that may not need to see.....it waste the resource...
And I come up with another solution, I make a new set of DBCmd, that allow me to get the related DB items, for example:
class getReleatedPurchaseRecordDBCmd{
public _constructor($aCustomerObject){
}
//.... ....
}
But in this "solution", I got some problems, is I loss the relationship in the object customer...yes, I can read back all the records, get the customer object basically don't know any things about the purchase record....
Some may ask me to do something like this:
class customer{
//skip other methods...
public getPurchaseRecords(){
//query the db
}
}
It works, but I don't want the object structure have some strong relationship between the db....That's why I come up with the DBCmd stuff...
So, everything seems to be very coupling, how can solve it? Thank you.

Answer 1

for stuff like this i tend to get the count of sub objects with the initial query usually involving sql COUNT and JOIN, then have a seperate getSubObjects command that can be called if needed later. So for example:
$datamodel->getCustomer($id);//or some such method
returns
class Customer{
$id = 4;
$recordCount = 5;
$records = null;
}
I can then use the count for any display stuff as needed, and if i need the records populated call:
$customer->records = $datamodel->getCustomerRecords($customer->id);