Getting types of the attributes in an ActiveRecord object

Question

I would like to know if it is possible to get the types (as known by AR - eg in the migration script and database) programmatically (I know the data exists in there somewhere).

For example, I can deal with all the attribute names:

ar.attribute_names.each { |name| puts name } 

.attributes just returns a mapping of the names to their current values (eg no type info if the field isn't set).

Some places I have seen it with the type information:

in script/console, type the name of an AR entity:

>> Driver => Driver(id: integer, name: string, created_at: datetime, updated_at: datetime) 

So clearly it knows the types. Also, there is .column_for_attribute, which takes an attr name and returns a column object - which has the type buried in the underlying database column object, but it doesn't appear to be a clean way to get it.

I would also be interested in if there is a way that is friendly for the new "ActiveModel" that is coming (rails3) and is decoupled from database specifics (but perhaps type info will not be part of it, I can't seem to find out if it is).

Thanks.

Answer 1

In Rails 3, for your model "Driver", you want Driver.columns_hash.

Driver.columns_hash["name"].type  #returns :string 

If you want to iterate through them, you'd do something like this:

Driver.columns_hash.each {|k,v| puts "#{k} => #{v.type}"} 

which will output the following:

id => integer name => string created_at => datetime updated_at => datetime 

Answer 2

In Rails 5, you can do this independently of the Database. That's important if you use the new Attributes API to define (additional) attributes.

Getting all attributes from a model class:

pry> User.attribute_names => ["id",  "firstname",  "lastname",  "created_at",  "updated_at",  "email",... 

Getting the type:

pry> User.type_for_attribute('email') => #<ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter::MysqlString:0x007ffbab107698  @limit=255,  @precision=nil,  @scale=nil> 

That's sometimes more information than needed. There's a convenience function that maps all these types down to a core set (:integer, :string etc.)

> User.type_for_attribute('email').type => :string  

You can also get all that data in one call with attribute_types which returns a 'name': type hash.