保存django ORM模型没有变化有多贵？

Question

sometimes we have to do a Model instance.save() regardless if some field changed, just for security and fast development.

1. how expensive is this with django ORM?
2. signals are always sent?
3. any SQL query is executed?

I tested with django debug toolbar to do 10 .save() in different points where anything in the model has changed, and the log does not register sql queries.

other way to test it or some article?

thank you in advance.

Answer 1

Im not entirely sure how you application handles this.

But i ran a small test:

a = Blog.objects.get(pk=1)

for b in range(1, 100):
    a.save()

This gave me a result of:

87.04 ms (201 queries)

Be ware as well that a save will do two queries:

SELECT ••• FROM `fun_blog` WHERE `fun_blog`.`id` = 1 LIMIT 1

UPDATE `fun_blog` SET `title` = 'This is my testtitle', `body` = 'This is a testbody' WHERE `fun_blog`.`id` = 1