Resolving N+1 Query Issue with select_related

Your approach with select_related("category", "user") is correct, but there might be a few issues causing the N+1 query problem.

The Issue

When you use {% if material.user == current_user %} in your template, Django should not be making additional queries if select_related("user") is properly configured. The select_related() method should prefetch the related User objects in a single query.

Possible Solutions

1. Verify select_related is working correctly

Make sure your query is actually executing with the select_related. Sometimes line breaks or indentation can cause issues:

PYTHONCopied
def get_materials(request):
    materials = Material.objects.select_related("category", "user").filter(
        Q(user=request.user) | Q(user__id=1)
    )
    context = {
        "materials": materials,
        "current_user": request.user,
    }
    return render(request, "table.html", context)

2. Compare IDs instead of objects

Instead of comparing the entire user objects, compare their IDs in the template:

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{% for material in materials %}
    {% if material.user.id == current_user.id %}
        <!-- ... some display logic ... --> 
    {% endif %}
{% endfor %}

3. Add a property to the Material model

Another approach is to add a property to your Material model that checks if a material belongs to a specific user:

PYTHONCopied
# models.py
class Material(models.Model):
    # your existing fields
    
    def belongs_to(self, user):
        return self.user_id == user.id

Then in your template:

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{% for material in materials %}
    {% if material.belongs_to current_user %}
        <!-- ... some display logic ... --> 
    {% endif %}
{% endfor %}

4. Annotate the queryset

You can also annotate your queryset to add a flag indicating if the material belongs to the current user:

PYTHONCopied
from django.db.models import Case, When, BooleanField, Value

def get_materials(request):
    materials = Material.objects.select_related("category", "user").filter(
        Q(user=request.user) | Q(user__id=1)
    ).annotate(
        is_owner=Case(
            When(user=request.user, then=Value(True)),
            default=Value(False),
            output_field=BooleanField(),
        )
    )
    context = {
        "materials": materials,
    }
    return render(request, "table.html", context)

Then in your template:

HTMLCopied
{% for material in materials %}
    {% if material.is_owner %}
        <!-- ... some display logic ... --> 
    {% endif %}
{% endfor %}

Debugging Tips

1. Check the actual SQL queries being executed using Django Debug Toolbar
2. Ensure your Material model has the ForeignKey to User properly defined
3. Verify that select_related is actually being applied (not overridden elsewhere)

The select_related() method should be working as expected based on the documentation, so one of these approaches should resolve your N+1 query issue.