Rails 4 Postgresql array data-type: updating values

Question

I am just starting to use the array data-type in Postgres with Rails 4 but I am having trouble getting values on an existing array to update. I have a column called 'quantity' that is an array of integers( [0,0] ). I want to update the value at 'quantity[0]' and I have tried the following in the console:

a = Asset.find(2) 
=> #<Asset id: 2, quantity: [0,0]>

a.quantity[0] = 5
=> 5 

a.quantity_will_change! 
=> [5, 0] 

a.save
=> true

a.reload
=> #<Asset id: 2, quantity: [0,0]>

As you can see, the asset object's quantity value is change but when I try to save the object using 'a.save' the change is not reflected when I reload the object.

Any help would be greatly appreciated.

Thanks

quantity_will_change! or replacing the whole array should work. Is there something going on that we can't see? — mu is too short
– mu is too short, Commented Nov 14, 2013 at 23:23
@muistooshort : you were 100% correct. I had a callback on my model that was altering the values. I appreciate the help. — degreesoffun
– degreesoffun, Commented Nov 19, 2013 at 16:49

Peter Alfvin · Accepted Answer · 2013-11-14 22:52:58Z

2

My reading of http://apidock.com/rails/ActiveRecord/Dirty is that you have to call ..._will_change! before you change the attribute. You should be able to confirm this by examining changes under various scenarios.

Update: I just tested the behavior with a string attribute, and it still saves the updated string even if the change was made before ..._will_change is called, so my interpretation may be off.

edited Nov 14, 2013 at 22:52

answered Nov 14, 2013 at 22:46

Peter Alfvin

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2 Comments

degreesoffun Over a year ago

Hey Peter, I have tried using quantity_will_change! both before and after setting the value. The changes method does in fact show that the value was changed. Any other ideas? Thanks for your help.

Peter Alfvin Over a year ago

Only thing I can think of is what @muistooshort indicated, that something else is going on (e.g. within your model that is "resetting" things).

dredozubov · Accepted Answer · 2014-05-29 22:19:41Z

1

<attribute>_will_change! will only update value if array has been replaced. In-place modifications like []= won't be saved at all.

answered May 29, 2014 at 22:19

dredozubov

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