Duplicate SQL queries in Django Senko Rašić, Good Code 

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models.py:! ! class Author(Model): name = CharField(…) ! class Book(Model): author = ForeignKey(Author, …) title = CharField(…) ! views.py:! ! books = Book.objects.all() ! template.html:! ! {% for book in books %} {{ book.title }} {% endfor %} 

models.py:! ! class Author(Model): name = CharField(…) ! class Book(Model): author = ForeignKey(Author, …) title = CharField(…) ! views.py:! ! books = Book.objects.all() ! template.html:! ! {% for book in books %} {{ book.title }} by {{ book.author.name }} {% endfor %} 

models.py:! ! class Author(Model): name = CharField(…) ! class Book(Model): author = ForeignKey(Author, …) title = CharField(…) ! views.py:! ! books = Book.objects.all().select_related(‘author’) ! template.html:! ! {% for book in books %} {{ book.title }} by {{ book.author.name }} {% endfor %} 

Know thy SQL 

django.test.TestCase.assertNumQueries() 

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[SQL] repeated query (1000x): SELECT “author"."id", “author”.”name” FROM "author" WHERE "author"."id" = ? [SQL] 1007 queries (1000 duplicates), 945 ms SQL time, 24351 ms total request time django-queryinspect 

SELECT “author”."id", “author”.”name” FROM "author" WHERE "author"."id" = 1 SELECT “author”."id", “author”.”name” FROM "author" WHERE "author"."id" = 2 SELECT “author”."id", “author”.”name” FROM "author" WHERE "author"."id" = 3 ! … ! SELECT “author”."id", “author”.”name” FROM "author" WHERE "author"."id" = ? django-queryinspect 

X-QueryInspect-Num-SQL-Queries: 1007 X-QueryInspect-Duplicate-SQL-Queries: 1000 X-QueryInspect-Total-SQL-Time: 945 ms X-QueryInspect-Total-Request-Time: 24351 ms django-queryinspect 

File "/vagrant/api/views.py", line 178, in get return self.serialize(self.object_qs) File "/vagrant/customer/views.py", line 131, in serialize return serialize(objs, include=includes) File "/vagrant/customer/serializers.py", line 258, in serialize_contact lambda obj: [r.name for r in obj.roles.all()]), File "/vagrant/customer/serializers.py", line 258, in lambda obj: [r.name for r in obj.roles.all()]), ! [SQL] repeated query (6x): SELECT "customer_role"."id", "customer_role"."contact_id", "customer_role"."name" FROM "customer_role" WHERE "customer_role"."contact_id" = ? django-queryinspect 

Copy production DB to staging server 

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