CODEWITHSUNDEEP
djangopostgresqldjango-rest-framework
John doe
John doe

Reputation: 3870

How to properly increment a counter in my postgreSQL database?

Let's say i want to implement a "Like/Unlike" system in my app. I need to count each like for sorting purposes later. Can i simply insert the current value + 1 ? I think it's too simple.

What if two user click on the same time ? How to prevent my counter to be disturbed ?

I read i need to implement transactions by a simple decorator @transaction.atomic but i am wonder if this can handle my concern.

Transactions are designed to execute a "bloc" of operations triggered by one user, whereas in my case i need be able to handle multiple request at the same time and safely update the counter.

Any advise ?

Upvotes: 1

Views: 510

Answers (1)

Saji Xavier
Saji Xavier

Reputation: 2360

You can use F() expression, eg.

content.likes_count = F('likes_count') + 1
content.save()

So the operation will be excuted in database not in python.

From the django documentation.

Another useful benefit of F() is that having the database - rather than Python - update a field’s value avoids a race condition.

If two Python threads execute the code in the first example above, one thread could retrieve, increment, and save a field’s value after the other has retrieved it from the database. The value that the second thread saves will be based on the original value; the work of the first thread will simply be lost.

If the database is responsible for updating the field, the process is more robust: it will only ever update the field based on the value of the field in the database when the save() or update() is executed, rather than based on its value when the instance was retrieved.

Upvotes: 2

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