I know in elixir data types are immutable. I have a column name failed_login_tries. which is integer and i want to increment it every time user put incorrect password. this is the code defp check_chromatic_password(plaintext, %User{} = user) do if Bcrypt.checkpw(plaintext, user.local_password_h…

You can change the user struct by using user = %{ user | failed_login_tries: user.failed_login_tries + 1} and to persist this in the database use Repo.update by passing it an updated ecto changeset. Immutability refers to the fact that the previous struct remains the same. e.g. defmodule User do …

Just be aware that there is an inherent race condition with that approach: if the user fails auth in quick succession twice both may have the user record with the current count prior to either auth attempt, and so both will increment the old value by one and update the db with that, causing the N at…

There’s an even simpler option to write that query: from(u in User, update: [inc: [failed_login_tries: 1]], where: u.id == user.id) )

I always forget about inc (and friends) .. thanks for the reminder!

This way of expressing a query, does that mean I can only get this update passing it to an update_all()? At first I was trying to pass it to a one() since I know I will get only one result, but it doesn’t seem to work.

[image] tjdam: This way of expressing a query, does that mean I can only get this update passing it to an update_all()? That’s correct.

[image] LostKobrakai: from(u in User, update: [inc: [failed_login_tries: 1]], where: u.id == user.id) ) Is there a “correct” way to update the timestamps() (:updated_at) when doing this? I mean I know I can add set: [updated_at: ....] to the query and pass the current time but that doesn’t se…

It is though. Updating timestamps is a “schema” feature, which is not supported by the lower level *_all api’s on the repo.

[image] LostKobrakai: Updating timestamps is a “schema” feature Does it use the “elixir time” or the “database time” for this? If it uses “database time” then I’d need the same to pass to the set: [updated_at: <here>]. I am not yet the whole codebase savvy enough to quickly find and verify it…

Timestamps use the autogenerate functionality of ecto schema fields, which is runtime functionality. So those are not set on the db.

What do you think of the approach shown here: [NoDisplayName] Elixir Ecto - How to Upsert/Increment elixir, phoenix-framework, ecto answered by NoDisplayName on 07:24AM - 10 Feb 17 UTC Right - locking is costly but in this pa…

How to increment database table column

Questions & Help Questions

benwilson512 April 19, 2020, 4:36am 7

That’s correct.