Eval on LHS of Assignment

rubyonrails-talk
1

I want to set the values of several record fields from within an iterator where the field name is passed as a parameter. For example (conceptually):

# Line numbers are for reference only and are not a part of the code. 1. record=Model.find(id) 2. params.each do |key,value| 3. eval('record.'+key)=value 4. end

Apparently, having the eval on the LHS of an assignment doesn't work. Can anyone please tell me what would work?

Thanks for any input.

         ... doug

2

Doug Jolley wrote:

I want to set the values of several record fields from within an iterator where the field name is passed as a parameter. For example (conceptually):

# Line numbers are for reference only and are not a part of the code. 1. record=Model.find(id) 2. params.each do |key,value| 3. eval('record.'+key)=value 4. end

Apparently, having the eval on the LHS of an assignment doesn't work. Can anyone please tell me what would work?

record[key] = value

Note that this relies on the hash-like behavior of ActiveRecord. If you wanted to do this with a non-AR object, you could use record.send("#{key}=", value). eval is rarely necessary in Ruby.

However, in this case, you could just do record.update_attributes(params).

Thanks for any input.

         ... doug

--

Best,

3

First of all if you are doing this from a controller, you probably don't want to use ALL of the parameters, but only those for the model, probably coming from a form,

For an active record model you can do:

# Assuming that the model really is called Model, and you are following Rails conventions for the form: model_params = params[:model] ||

model_params.each do |key, value|    record[key] = value end

or just

record.attributes=(model_params, false)

The false overrides the protection of attributes, and probably isn't a good idea in general. You normally don't want to blindly mass assign any attributes the user throws at you. Consider the fact that the incoming url might be coming from a form submission from your app, or might be forged.

4

Wow, two really thorough answers. Thanks so much. Sorry for the delay in responding. I wanted to see if I couldn't get this thing working before responding; but, alas, I ran into other problems. However, I would have to say that this issue has definitely been put to bed. Thanks for the input.

Oh, BTW:

# Assuming that the model really is called Model,

It isn't. I chose that name for illustrative purposes.

Thanks to all for the input.

       ... doug