update and save database in a create method using same form rails -

i trying use same form create new database entry, display current db information, , update db information, stuck trying patch in create method within controller. have tried using first_or_initialize , find_or_initialize_by_name, cant seem them work situation. thinking of trying if something.nil? / else type of design. new @ , appreciated!

this controller (working create new db):

    def create      params[:student].each |student_id, attendance_type|       attendance = attendance.new       attendance.attendance_type = attendance_type.to_i       attendance.student_id = student_id       attendance.event_id = params[:event_id]       attendance.save     end      redirect_to :back    end 

html:

    <tbody>      <% @students.each |student| %>       <form class="form-group" action="/events/<%= @event.id %>/attendances" method="post">       <tr>       <div class="checkbox">         <td style="white-space:normal;"><%= link_to student.name, student_path(student.id) %></td>          <% attendance = student.attendances.find_by_event_id(@event.id) %>         <% if attendance.blank? || attendance.attendance_type == 1 %>           <td style="white-space:normal;"><label class="radio-inline"><input type="radio" name="student[<%= student.id %>]" checked="checked" id="inlineradio1" value="1"></label></td>           <td style="white-space:normal;"><label class="radio-inline"><input type="radio" name="student[<%= student.id %>]" id="inlineradio2" value="2"></label></td>           <td style="white-space:normal;"><label class="radio-inline"><input type="radio" name="student[<%= student.id %>]" id="inlineradio3" value="3"></label></td>         <% elsif attendance.attendance_type == 2 %>           <td style="white-space:normal;"><label class="radio-inline"><input type="radio" name="student[<%= student.id %>]" id="inlineradio1" value="1"></label></td>           <td style="white-space:normal;"><label class="radio-inline"><input type="radio" name="student[<%= student.id %>]" checked="checked" id="inlineradio2" value="2"></label></td>           <td style="white-space:normal;"><label class="radio-inline"><input type="radio" name="student[<%= student.id %>]" id="inlineradio3" value="3"></label></td>         <% else attendance.attendance_type == 3 %>           <td style="white-space:normal;"><label class="radio-inline"><input type="radio" name="student[<%= student.id %>]" id="inlineradio1" value="1"></label></td>           <td style="white-space:normal;"><label class="radio-inline"><input type="radio" name="student[<%= student.id %>]" id="inlineradio2" value="2"></label></td>           <td style="white-space:normal;"><label class="radio-inline"><input type="radio" name="student[<%= student.id %>]" checked="checked" id="inlineradio3" value="3"></label></td>         <% end %>       </div>     <% end %>     </tr>         <tr><%= button_to 'submit', :class => 'btn btn-primary' %></tr>  </form>     </tbody> 

thank in advance!

hopefully missing piece. not believe efficiency. explain after.

using attribute existing model following either find or create attendance object student id 10.

attendance.where(:student_id => 10).first_or_create |attendance|   attendance.event_id = 3 #arbitrary   attendance.attendance_type = 2 #arbitrary end 

or

attendance = attendance.where(:student_id => 10).first_or_initialize # bunch of ways set attributes # ... , attendance.save 

now, why may inefficient. if going through each student parameter , looping through attribute incur multiple calls. example, 100 students end doing 100 separate queries if loop first_or_initialize on every student attribute set. suggest mapping of parameters require 1 array, doing query , looping through array. put them 1 create call array, , bam cut serious activerecord overhead.

#just giving context student param keys student_ids = params[:student].keys  #query student ids attendances = attendance.where(student_id: student_ids)  #get list of ids filtering out of existing ids new_student_ids = student_ids - attendances.map{|a| a.student_id} #create array carry hashes attendances = array.new #cycle through of non-created ids , build create list new_student_ids.each |id|   attendances << {#assign values hash grabbing them params[:student] using iterating id} end   #create bunch @ once attendance.create attendances