I have a method that needs to loop through a hash and check if each key exists in a model's table, otherwise it will delete the key/value.
For example:
number_hash = { :one => "one", :two => "two" } and the Number table only has a :one column so :two will be deleted.
How do I check if a model has an attribute or not?
For a class
Use Class.column_names.include? attr_name where attr_name is the string name of your attribute.
In this case: Number.column_names.include? 'one'
For an instance
Use record.has_attribute?(:attr_name) or record.has_attribute?('attr_name') (Rails 3.2+) or record.attributes.has_key? attr_name.
In this case: number.has_attribute?(:one) or number.has_attribute?('one') or number.attributes.has_key? 'one'
Hash#select: number_hash.select { |key, value| Number.column_names.include? key }
number.has_attribute? which accepts a Symbol or a String
user, but had to instead look for user_id since some models delegated user.
Number.attribute_method? 'one'
record.try(:column_name) it will return then nil if column not existsIf you need to check for aliases as well, you can use Number.method_defined? attr_name or number.class.method_defined? attr_name.
I had to do this for a Mongoid object that had aliased fields.
ModelName.attribute_method? :attr_name was what worked in my instanceIn your instance object, you could use also defined? instance.attribute or instance.respond_to? :attribute.
These are more generic solution to check a model attribute or any method as well.
instance.respond_to?(:attribute) == false ; instance.attribute ; instance.respond_to?(:attribute) == trueif very simplified
for Model columns < attributes < methods
for record columns = attributes < methods
Model.columns <> Model.record.columns/attributes
column
Checking the existence of a column for a model Foo.column_names.include? 'column_name'
Does the column exist for the record? foo.has_attribute?('column_name')
attribute
Checking the existence of a attribute for a model Foo.attribute_method?(:attribute_name)
Does the attribute exist for the record? foo.has_attribute?(:attribute_name)
method
Checking the existence of a method for a class Foo.method_defined?(:method_name)
Does the method exist for the instance? foo.respond_to?(:method_name)
