How to create a new record or update if a particular record based on an attribute other than record id exists, Ruby on Rails?

问题

I have 2 model classes, employee & company. Only an employee id is generated by an external library. I am trying to update an employee details if his details already exist, else I need to create a new employee details. following is the code for create method:

def create

 if !@emp= Details.find_or_create_by_emp_id(params[:details][:emp_id])
    @emp = Details.new(params[:details])

  // some logic goes here 


  else
    @emp.update_attributes(params[:details])
    render action: "show"
  end      
end

But this always creates a new record with existing emp_id, rather than updating the table row pertaining to a specific emp_id. How to make it work ?

回答1:

You could try this:

def create
  @emp = Details.find_by_emp_id(params[:details][:emp_id])

  if @emp
    @emp.update_attributes(params[:details])
    render action: "show"
  else
    @emp = Details.new(params[:details])
    //other stuff
  end
end

So if the employee already exists it's set to @emp, otherwise @emp is set to nil

回答2:

You're using find_or_create wrong. It takes both the identifier and the hash:

 if Detail.find_or_create_by_emp_id(params[:detail][:emp_id], params[:detail])
   #success
 else
   #fail
 end

Note: both your Model name and param seems to be plural, that's against convention, are you sure that's what you intended?

来源：https://stackoverflow.com/questions/12012728/how-to-create-a-new-record-or-update-if-a-particular-record-based-on-an-attribut