Rails Postgres hstore. DB not being updated with changed values

Question

I'm trying to understand how to use hstore and it seems the database isn't updated if I try to modify a value in my hash.

In my rails console I do

u = User.new
u.hash_column = {'key' => 'first'}
u.save

I get a message in my console (0.4ms) BEGIN SQL (2.0ms) UPDATE "users" SET "hash_column" = $1, "updated_at" = $2 WHERE ... (18.0ms) COMMIT and when I check in the DB the column has the correct data

now when I try

u.hash_column['key'] = 'second'

the model seems correct in the console

puts u.hash_column

gives {"key"=>"second"}

however when I try to save this u.save in my console I just get (0.3ms) BEGIN (0.2ms) COMMIT with no update statement and when I check the DB the data hasn't changed.

if I change another attribute on the user model and save it hash_column still doesn't get updated. The only way I can change the hash_column in the database seems to be to assign to the complete hash like

u.hash_column = {'key' => 'second'}

is this how it is meant to work or am I doing something wrong?

Answer 1

This is due to the way that rails currently tracks changes. It will only track changes when you use the attributes setter (u.hash_column). If you update a value in the hash, you have to notify Rails that the value changed by calling u.hash_column_will_change!. This marks the value as dirty and the next time save is called, it will be persisted.

This also effects arrays and strings and dates. If you call u.string_value.gsub! or u.array_column << value those changes will not be persisted without calling the <column>_will_change! method for those columns