How to sort an array of objects by an attribute of the objects?

Question

I'm performing this query in a controler and the 'Group' model has_many Users

@group= Group.find(params[:id]) 

@group is being used to render this partial (the partial dumps the users of a group into a table)

<%= render :partial=>"user_list", :locals=>{:users=>@group.users} %> 

The local variable 'users' passed to the partial is an array of User objects;

- !ruby/object:User    attributes:      updated_at: 2011-01-04 21:12:04     firstname:  Bob     lastname: Smith     id: "15"     group_id: "2"     created_at: 2010-11-26 12:54:45 

How can the user array be sorted by 'lastname'? I've tried several different ways without any luck. Trying to sort by a object attribute inside an array in confusing me. Also, I don't undertand how I could do this with an :order in the query (how to :order not the Group but the Users of each group)?

Maybe I'm not referring to name of the object correctly ('User')? It seems like this should work be it produces a 'no method' error (or a dynamic constant assignment error if 'sort_by' is used without the !):

 users.sort_by! {|User| User.lastname} 

Thanks for any help.

Answer 1

I found a method that works from here. I don't understand what the "&" symbol is doing - maybe it's shorthad for "object" since in my case ":lastname" is an attribute of the object that make up the array.

users = users.sort_by &:lastname 

note: I don't undertand why but a destructive version won't work. It produces a "undefined method `sort_by!' for #" errror:

users.sort_by! &:lastname