Rails form with custom path & getting missing required ID key -

i know i'm breaking rails convention somehow causing error, can't figure out what...

# controller def membership    @user = user.new(user_type:"member") end def membership_create    @user = user.find(params[:id])    ... end  # routes match '/membership/create.:id', to: "users#membership_create", via: :post, as: "create_member"  # view # have tried following based on various other answers, doesn't work <%= form_for @user, :url => create_member_path(@user), method: :post |f| %> <%= form_for @user, :url => create_member_path(@user) |f| %> 

consistently getting error message: no route matches {:action=>"membership_create", :controller=>"users", :id=>nil} missing required keys: [:id]

why not /membership/create/:id opposed /membership/create.:id?

but then, building new user membership method:

def membership   @user = user.new(user_type:"member") end 

and user has no id yet. so, when passing path form:

<%= form_for @user, :url => create_member_path(@user) |f| %> 

the id nil.

however, membership_create requires id? - ( configured in route ) remember nil @ point. unless have miraculously included id somewhere in loop, can't see, or 2 methods not directly related think.