get model attribute dynamically in rails 3

Question

How can I get the attribute from the model object dynamically? I have the attribute of the User object as string:

u = User.find(1)

Can I do something like u.get("user_id")

I'm not totally understanding this question. What exactly are you trying to do? — Srdjan Pejic
– Srdjan Pejic, Commented May 13, 2011 at 18:58
Feel free to accept an answer from some given below if you're happy? Not close to what you need? — Aditya Sanghi
– Aditya Sanghi, Commented May 16, 2011 at 10:05
If you're talking about only ActiveRecord objects (as in the code example), you should probably be more explicit about it in the title and question. (I didn't realize this until I tried the answer.) The chosen answer treating the model as a hash only works for ActiveRecord objects and only for attributes that are columns. — cesoid
– cesoid, Commented Nov 15, 2014 at 17:51
I presume from context here that you mean to actually pull the attribute from the data store, otherwise it would be obvious to use u.user_id or one of several other simpler forms. — Tom Wilson
– Tom Wilson, Commented Nov 3, 2017 at 14:33

Aditya Sanghi · Accepted Answer · 2014-04-19 18:04:21Z

26

You could try using the ActiveRecord model instance like a hash.

u = User.find(1)
name = u[:name]
field = "first_name"
first_name = u[field]

edited Apr 19, 2014 at 18:04

answered May 13, 2011 at 19:09

Aditya Sanghi

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3 Comments

MDaubs Over a year ago

+1 This is the conventional approach when the attribute name isn't known in advance.

cesoid Over a year ago

Note that this only works for attributes that are columns. It does not work for attributes made accessible through attr_accessor.

Tom Wilson Over a year ago

Yes, assuming "dynamically" means getting a fresh value of the attribute straight from the data store, then you must start by getting a fresh copy of the object from the data store, e.g. <active_record_class>.find(id) and then use the attribute value from the fresh copy as described here by @aditya-sanghi. The read_attribute method does not hit the database.

twmills · Accepted Answer · 2011-05-13 19:39:56Z

13

Yet another approach:

attr = :first_name
@user.read_attribute attr

answered May 13, 2011 at 19:39

twmills

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Comments

Scott · Accepted Answer · 2011-05-13 19:05:42Z

6

Try this

user = User.find(1)

then something like this should do what you require

user.send('field_name')

answered May 13, 2011 at 19:05

Scott

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2 Comments

justisb Over a year ago

When working with enum attributes, this is the only way I've found that returns the field as a string rather than its raw integer value.

Jason Over a year ago

user.public_send('field_name') also works and is more secure

Harish Shetty · Accepted Answer · 2011-05-13 19:05:35Z

1

Try this

u = User.find(1)
attr = "first_name"
u.send(attr)

answered May 13, 2011 at 19:05

Harish Shetty

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Comments

Tam · Accepted Answer · 2011-05-13 19:04:40Z

0

Not sure if I totally understand your questions. Try something like:

User.find(1).name

if you mean you only want to fetch from DB specific attribute you can do:

User.find(1,:select => :name)

answered May 13, 2011 at 19:04

Tam

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