how to use Ajax

code :

Area

<%= f.select :area_id, Area.all.collect {|p| [ p.name, p.id ] }, :class=>“small” %>

Milk Mans

<%= f.select :milkman_id, Milkman.all.collect {|p| [ p.name, p.id ] }, :class=>“small” %>

When i select any area then i should see only those milkmans of that area.

Till now i getting all milkmans in my select box.

How to do this with Ajax ?

Hope u will understand question now ?

is any one know this

Stop. This is basic JavaScript/AJAX stuff, and has little to nothing to
do with Rails.

Find a tutorial on JS/AJAX and learn how it works. Then come back
here if you have a specific problem integrating it with your Rails code.