How to get one columns as an array from database

rubyonrails-talk
1

I have a table named "Projects" which has a column "name". I want to get a string array to represent all the name values. In the controller, I can use this code "@projects = Project.find(:all)" to get all the projects but how to convert it to the string array?

thanks.

2

Maybe a map will do the trick

@project_names = Project.all.map { |p| p.name }

3

Maybe this is a bit off topic… I never knew you could use syntax like Project.all. When was this added to the language/framework?

4

I think it's been around since Rails 2.1

Project.first Project.last Project.all

all work.

5

A more efficient way is to do this is:

@project_names = Project.all(:select => 'name').map(&:name)

6

Ryan wrote:

I think it's been around since Rails 2.1

Project.first Project.last Project.all

all work.

I think the first last and all refers to rows. I want to select columns.

7

Ryan wrote:

A more efficient way is to do this is:

@project_names = Project.all(:select => 'name').map(&:name)

Yes the map is what I am looking for.

thanks.

8

Zhao Yi wrote:

Ryan wrote:   

I think it's been around since Rails 2.1

Project.first Project.last Project.all

all work.      I think the first last and all refers to rows. I want to select columns.   

If I'm not wrong, relational algebra doesn't identify a sequence between the elements of a row, i.e., I don't think it gives you the ability to select a column specifically. That said, you could probe for the schema and get the elements using that - something like how the dynamic scaffold used to work in earlier Rails.

Cheers, Mohit. 12/26/2008 | 1:27 PM.

9

Zhao,

I think the most straightforward way is using columns.map (Project.columns.map { |c| puts c.name }), just like the inspect method of ActiveRecord:

inspect()

Returns a string like ‘Post id:integer, title:string, body:text‘

# File vendor/rails/activerecord/lib/active_record/base.rb, line 1348 1348: def inspect 1349: if self == Base 1350: super 1351: elsif abstract_class? 1352: "#{super}(abstract)" 1353: elsif table_exists? 1354: attr_list = columns.map { |c| "#{c.name}: #{c.type}" } * ', ' 1355: "#{super}(#{attr_list})" 1356: else 1357: "#{super}(Table doesn't exist)" 1358: end 1359: end

Cheers, Sazima

10

A more efficient way is to do this is: @project_names = Project.all(:select => 'name').map(&:name)

While you've made a database optimisation there, you've also used the shorthand notation for the map function. I read somewhere that map (&:name) is quite a bit less efficient than map{ |p| p.name }

unfortunately I can't find the article that convinced me in the first place... I can only find this blog with the issue mentioned in the comments:

http://blog.hasmanythrough.com/2006/3/7/symbol-to-proc-shorthand

11

Jonathan Fantham wrote:

12

Cool. Learn something new all the time.

Thanks.