PYTHON

django prefetch_related vs select_related

class ModelA(models.Model):
    pass

class ModelB(models.Model):
    a = ForeignKey(ModelA)

ModelB.objects.select_related('a').all() # Forward ForeignKey relationship
ModelA.objects.prefetch_related('modelb_set').all() # Reverse ForeignKey relationship

django select_related and prefetch_related

* django select_related and prefetch_related
* Prefetch_related and select_related functions in django
---------------------------------
select_related() “follows” foreign-key relationships,
selecting additional related-object data when it executes its query.

prefetch_related() does a separate lookup for each relationship, 
and does the “joining” in Python.
-------------------
Example

class A(models.Model):
pass

class B(models.Model):
a = ForeignKey(ModelA)
# Forward ForeignKey relationship
A.objects.select_related('a').all()
# Reverse ForeignKey relationship
A.objects.prefetch_related('modelb_set').all()

prefetch_related list django

# Use the magic syntax with "*" to expand the list
Knight.objects.all().prefetch_related(*selected_attributes)

django select_related and prefetch_related

django select_related and prefetch_related

select_related >> foreignkey
prefetch_related >> many to many
basically they are performance boosters ,used to avoid multiple unnecessary queries
Both methods achieve the same purpose, to forego unnecessary db queries. 
But they use different approaches for efficiency..