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What is the usage of `FilteredRelation()` objects in Django ORM (Django 2.X)?

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2

1

I've seen Django 2.0 consists of FilteredRelation object in queryset. What is the usage of newly introduced FilteredRelation?

What I've looked into?

I observed Django 2.0 Documentation but I could not understand idea behind this FilteredRelation object.

I looked into following code. But I didn't get it.

>>> from django.db.models import FilteredRelation, Q
>>> Restaurant.objects.annotate(
... pizzas_vegetarian=FilteredRelation(
... 'pizzas', condition=Q(pizzas__vegetarian=True),
... ),
... ).filter(pizzas_vegetarian__name__icontains='mozzarella')

Main Question

Show now my question is that what is usage of FilteredRelation and when to use in your QuerySet?

django django-models django-orm

share|improve this question

asked Mar 28 at 6:13

Devang PadhiyarDevang Padhiyar

1,24488 silver badges2424 bronze badges

add a comment | 

2

1

I've seen Django 2.0 consists of FilteredRelation object in queryset. What is the usage of newly introduced FilteredRelation?

What I've looked into?

I observed Django 2.0 Documentation but I could not understand idea behind this FilteredRelation object.

I looked into following code. But I didn't get it.

>>> from django.db.models import FilteredRelation, Q
>>> Restaurant.objects.annotate(
... pizzas_vegetarian=FilteredRelation(
... 'pizzas', condition=Q(pizzas__vegetarian=True),
... ),
... ).filter(pizzas_vegetarian__name__icontains='mozzarella')

Main Question

Show now my question is that what is usage of FilteredRelation and when to use in your QuerySet?

django django-models django-orm

share|improve this question

asked Mar 28 at 6:13

Devang PadhiyarDevang Padhiyar

1,24488 silver badges2424 bronze badges

add a comment | 

I've seen Django 2.0 consists of FilteredRelation object in queryset. What is the usage of newly introduced FilteredRelation?

What I've looked into?

I observed Django 2.0 Documentation but I could not understand idea behind this FilteredRelation object.

I looked into following code. But I didn't get it.

>>> from django.db.models import FilteredRelation, Q
>>> Restaurant.objects.annotate(
... pizzas_vegetarian=FilteredRelation(
... 'pizzas', condition=Q(pizzas__vegetarian=True),
... ),
... ).filter(pizzas_vegetarian__name__icontains='mozzarella')

Main Question

Show now my question is that what is usage of FilteredRelation and when to use in your QuerySet?

django django-models django-orm

share|improve this question

asked Mar 28 at 6:13

Devang PadhiyarDevang Padhiyar

1,24488 silver badges2424 bronze badges

>>> from django.db.models import FilteredRelation, Q
>>> Restaurant.objects.annotate(
... pizzas_vegetarian=FilteredRelation(
... 'pizzas', condition=Q(pizzas__vegetarian=True),
... ),
... ).filter(pizzas_vegetarian__name__icontains='mozzarella')

share|improve this question

asked Mar 28 at 6:13

Devang PadhiyarDevang Padhiyar

1,24488 silver badges2424 bronze badges

share|improve this question

asked Mar 28 at 6:13

Devang PadhiyarDevang Padhiyar

1,24488 silver badges2424 bronze badges

asked Mar 28 at 6:13

Devang PadhiyarDevang Padhiyar

1,24488 silver badges2424 bronze badges

asked Mar 28 at 6:13

Devang PadhiyarDevang Padhiyar

1,24488 silver badges2424 bronze badges

1 Answer
1

active

oldest

votes

4

I think the documentation itself self-explanatory.

You could achieve the same result in,
Method-1

from django.db.models import FilteredRelation, Q

result_1 = Restaurant.objects.annotate(pizzas_vegetarian=FilteredRelation('pizzas', condition=Q(pizzas__vegetarian=True), ), ).filter(
 pizzas_vegetarian__name__icontains='mozzarella')

Method-2

result_2 = Restaurant.objects.filter(pizzas__vegetarian=True, pizzas__name__icontains='mozzarella')

You will get better performance with Method-1 since the filtering in the WHERE clause of the first queryset will only operate on vegetarian pizzas.

---

UPDATE

The Django #29555 ticket has more information regarding the usage and performance.


The FilteredRelation() not only improves performance but also creates
correct results when aggregating with multiple LEFT JOINs.

share|improve this answer

edited Mar 28 at 8:37

answered Mar 28 at 6:30

JPGJPG

22.4k33 gold badges1515 silver badges4747 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Does both of the query returns same results?
  
  – Devang Padhiyar
  Mar 28 at 6:32
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes. But, you can't use FilteredRelation always because it has some restrictions. (specified on FilteredRelation doesn’t support section of the doc)
  
  – JPG
  Mar 28 at 6:34
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Should I use F('field_name') within condition
  
  – Devang Padhiyar
  Mar 28 at 8:39
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Nop, because an F() object represents the value of a model field or annotated column.
  
  – JPG
  Mar 28 at 8:40
  
  

  
  
  
  

add a comment | 

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4

I think the documentation itself self-explanatory.

You could achieve the same result in,
Method-1

from django.db.models import FilteredRelation, Q

result_1 = Restaurant.objects.annotate(pizzas_vegetarian=FilteredRelation('pizzas', condition=Q(pizzas__vegetarian=True), ), ).filter(
 pizzas_vegetarian__name__icontains='mozzarella')

Method-2

result_2 = Restaurant.objects.filter(pizzas__vegetarian=True, pizzas__name__icontains='mozzarella')

You will get better performance with Method-1 since the filtering in the WHERE clause of the first queryset will only operate on vegetarian pizzas.

---

UPDATE

The Django #29555 ticket has more information regarding the usage and performance.


The FilteredRelation() not only improves performance but also creates
correct results when aggregating with multiple LEFT JOINs.

share|improve this answer

edited Mar 28 at 8:37

answered Mar 28 at 6:30

JPGJPG

22.4k33 gold badges1515 silver badges4747 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Does both of the query returns same results?
  
  – Devang Padhiyar
  Mar 28 at 6:32
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes. But, you can't use FilteredRelation always because it has some restrictions. (specified on FilteredRelation doesn’t support section of the doc)
  
  – JPG
  Mar 28 at 6:34
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Should I use F('field_name') within condition
  
  – Devang Padhiyar
  Mar 28 at 8:39
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Nop, because an F() object represents the value of a model field or annotated column.
  
  – JPG
  Mar 28 at 8:40
  
  

  
  
  
  

add a comment | 

4

I think the documentation itself self-explanatory.

You could achieve the same result in,
Method-1

from django.db.models import FilteredRelation, Q

result_1 = Restaurant.objects.annotate(pizzas_vegetarian=FilteredRelation('pizzas', condition=Q(pizzas__vegetarian=True), ), ).filter(
 pizzas_vegetarian__name__icontains='mozzarella')

Method-2

result_2 = Restaurant.objects.filter(pizzas__vegetarian=True, pizzas__name__icontains='mozzarella')

You will get better performance with Method-1 since the filtering in the WHERE clause of the first queryset will only operate on vegetarian pizzas.

---

UPDATE

The Django #29555 ticket has more information regarding the usage and performance.


The FilteredRelation() not only improves performance but also creates
correct results when aggregating with multiple LEFT JOINs.

share|improve this answer

edited Mar 28 at 8:37

answered Mar 28 at 6:30

JPGJPG

22.4k33 gold badges1515 silver badges4747 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Does both of the query returns same results?
  
  – Devang Padhiyar
  Mar 28 at 6:32
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes. But, you can't use FilteredRelation always because it has some restrictions. (specified on FilteredRelation doesn’t support section of the doc)
  
  – JPG
  Mar 28 at 6:34
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Should I use F('field_name') within condition
  
  – Devang Padhiyar
  Mar 28 at 8:39
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Nop, because an F() object represents the value of a model field or annotated column.
  
  – JPG
  Mar 28 at 8:40
  
  

  
  
  
  

add a comment | 

I think the documentation itself self-explanatory.

You could achieve the same result in,
Method-1

from django.db.models import FilteredRelation, Q

result_1 = Restaurant.objects.annotate(pizzas_vegetarian=FilteredRelation('pizzas', condition=Q(pizzas__vegetarian=True), ), ).filter(
 pizzas_vegetarian__name__icontains='mozzarella')

Method-2

result_2 = Restaurant.objects.filter(pizzas__vegetarian=True, pizzas__name__icontains='mozzarella')

You will get better performance with Method-1 since the filtering in the WHERE clause of the first queryset will only operate on vegetarian pizzas.

---

UPDATE

The Django #29555 ticket has more information regarding the usage and performance.


The FilteredRelation() not only improves performance but also creates
correct results when aggregating with multiple LEFT JOINs.

share|improve this answer

edited Mar 28 at 8:37

answered Mar 28 at 6:30

JPGJPG

22.4k33 gold badges1515 silver badges4747 bronze badges

from django.db.models import FilteredRelation, Q

result_1 = Restaurant.objects.annotate(pizzas_vegetarian=FilteredRelation('pizzas', condition=Q(pizzas__vegetarian=True), ), ).filter(
 pizzas_vegetarian__name__icontains='mozzarella')

result_2 = Restaurant.objects.filter(pizzas__vegetarian=True, pizzas__name__icontains='mozzarella')

share|improve this answer

edited Mar 28 at 8:37

answered Mar 28 at 6:30

JPGJPG

22.4k33 gold badges1515 silver badges4747 bronze badges

answered Mar 28 at 6:30

JPGJPG

22.4k33 gold badges1515 silver badges4747 bronze badges

answered Mar 28 at 6:30

JPGJPG

22.4k33 gold badges1515 silver badges4747 bronze badges