Rails中新的关联对象的渲染形式

Question

I am having trouble with creating association;

My models are Table and Columns (one table to many columns).

In my ColumnsController:

def new
    @table = Table.find(params[:id])
    @column = @table.columns.build
end  

In my app/views/tables/show.html.erb:

<%= @table.name %></dd>
<%= render "columns/form" %>

In my app/views/columns/_form.html.erb:

<%= form_for  @column, :url => {:action => :create, :id => @table.id }do |f| %>
<%= f.label :name  %>
<%= f.text_field :name %>
<%= f.button :submit%><% end %>

When I run it:

undefined method `model_name' for NilClass:Class
Extracted source (around line #1):
<%= form_for  @column, :url => {:action => :create, :id => @table.id } do |f| %>

Why ? :-(

Answer 1

Try doing it with partials and local variables:

<%= render partial: "columns/form", locals: {table: @table, column: @column} %>

and

<%= form_for  column, :url => {:action => :create, :id => table.id }do |f| %>

If you want it even simpler, you can do this:

<%= render partial: "columns/form", locals: {table: @table} %>

and

<%= form_for table.columns.new do |f| %>