Hi,
Python/Django newb here. I have a question regarding the best
approach to rendering 1-to-many relationships in a template.
I have 2 tables, Customers and Cars, where a Customer can have many
Cars, hence the 1-to-many relationship. I need to display all the
Customers with all their Cars, like this:
Customer1
Car: car1
Car: car2
Customer2
Car: car1
Car: car2
Car: car3
...
I've taken 2 approaches to solving this problem, described below.
The first approach involves creating a complete Customers queryset,
and then using a FOR loop inside the template to create a Cars
queryset, once for each customer. The problem is obvious: if I have
10,000 customers, the Cars table is going to be queried 10,000 times
(correct?). The DBA is going to be mad, and I'm going to look
foolish. Here's the code:
{% for customer in customers %}
<li>{{ customer.full_name }}</li>
<ul>
{% for car in customer.car_set.all %}
<li>Car: {{ car }}</li>
{% endfor %}
</ul>
{% endfor %}
My second approach involves both complete Customers and Cars
querysets. Then, inside the template, iterate through the Cars
queryset based on the current Customer.id, and then output the car.
Here's the code:
{% for customer in customers %}
<li>{{ customer.full_name }}</li>
<ul>
{% for car in cars %}
{% ifequal car.customer_id customer.id %}
<li>Car: {{ car }}</li>
{% endifequal %}
{% endfor %}
</ul>
{% endfor %}
I *think* the problem with the 2nd approach is that I'm forcing Python
to iterate through the Cars queryset 10,000 times to find the car(s)
belonging to each driver.
Is there a 3rd, better/best approach to this problem? Thanks!
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