CODEWITHSUNDEEP
django
Edgar Navasardyan
Edgar Navasardyan

Reputation: 4501

Using queryset manager with prefetch_related

I have been succesfully using this brilliant technique to keep my code DRY encapsulating ORM relations in querysets so that code in views is simple and not containing foreign key dependency. But this time I face the following issue best descriped by code:

View:

vendors_qs = vendors_qs.select_related().prefetch_related('agreement_vendors')

Model class AgreementVendorsQuerySet(models.query.QuerySet):

def some_filter1(self, option):
    result = self.filter(.....)
    return result

def some_filter2(self, option):
    result = self.filter(.....)
    return result

And a template:

{% for vendor in vendors_qs %}
    <tr>
        ...
        <td>
           {% for vend_agr in vendor.agreement_vendors.all %}
               {{vend_agr.serial_number}}
           {% endfor %}
        <td>
    </tr>
 {% endfor %}

The question is, how and where do I apply the some_filter1 to vendor agreements given that it is fetched as prefetch_related relation. Do I have to apply the filter in the template somehow or in the view itself ? If I didn't put the question clearly enough, I will ask your questions to clarify further...

UPDATE: Anna's asnwer looks very much like the truth, but one detail remains unclear. What if I want to apply several filters based on if-condition. For exapmle, if the filters were to apply to vendors, then the code would simply look like:

if (condition_1)
     vendors_qs = vendors_qs.filter1()
if (condition_2)
     vendors_qs = vendors_qs.filter2()

Upvotes: 0

Views: 1179

Answers (1)

Anna
Anna

Reputation: 553

If I clearly understand your question you need something like this

    vendors_qs = vendors_qs.prefetch_related(models.Prefetch('agreement_vendors', queryset=some_filter, to_attr='agreement_vendors_list'))

And then in template you can call it like {% for vend_agr in vendor.agreement_vendors_list %}

Upvotes: 2

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