Mongo - build table from two collections - php

Question

I am trying to replicate what would be a left join in MySql in Mongo. I have a collection named Clients and another collection name Orders.
In the clients collection is have:
client_PK, FirstName, LastName, Company
In the orders collection I have:
order_PK, client_fk, OrderDate, OrderAmount,
So i know that can use embedded documents but for the sake of this question i am looking to use the reference model.
My question is, using these two collections how would I construct a table or object similar to a left join in mysql? I know this is a document db not a relational db but im using sql language just to give you an idea of what im trying to accomplish. In MySql it would look like this:
SELECT * FROM orders LEFT JOIN clients ON clients.client_PK = orders.client_fk
with this i could now construct a table that looked like:
FirstName | LastName | Company | OrderDate | OrderAmount
then i could repeat the rows using a while loop to display all orders and display the clients name with the order. Again i know mongo isn't a relational db but i am assuming there is a way simulate a table using two collections.
Thank you.

Answer 1

You almost certainly want to be storing these data all in the same MongoCollection (even in just a denormalization collection).
If you absolutely can't do that, though, and if your set is small, you can do something similar to this (since you asked about PHP):
<?php
// gather orders
$orders = iterator_to_array($mongodb->orders->find());
$joinedOrders = array();
// gather clients
foreach ($db->clients->find() as $client) {
// iterate orders (like a left join)
foreach ($orders as $order) {
// make a "joinedOrders" record for each join match
if ($order['client_fk'] == $client['client_PK']) {
$joinedOrders[] = array_merge($order, $client);
}
}
}
// result is now in $joinedOrders
This is, however, almost always a bad idea. (-: You really should be denormalizing your data, or using a relational database to store/query relational data.

Answer 2

i am assuming there is a way simulate a table using two collections
MongoDB does not have any tool for doing this. You are basically going to have "roll your own" joins. At the basic level, this means that you will have to write nested for loops and build a result set in your code.
Doing this type of "extra logic" is pretty common in MongoDB because of the lack of joins. If you're seeing this pattern a lot, you may want to consider using SQL for part of your data.