undefined method on ActiveRecord::Relation object

问题

the following code

fieldvalue = Admin::FieldValue.where(:item_id => @admin_item.id, :field_id => key)
fieldvalue.update_attributes(:value => value)

raise the following error

NoMethodError (undefined method `update_attributes' for #<ActiveRecord::Relation:0x00000102dfc868>):

why is it a Relation object and not a FieldValue object, what's the right way to manage this

回答1:

fieldvalue should return only one value?

fieldvalue = Admin::FieldValue.where(:item_id => @admin_item.id, :field_id => key).first
fieldvalue.update_attributes(:value => value)

Or if you expect multiple items:

fieldvalue = Admin::FieldValue.where(:item_id => @admin_item.id, :field_id => key)
fieldvalue.update_all(:value => value)

来源：https://stackoverflow.com/questions/11107775/undefined-method-on-activerecordrelation-object