about active record read and write attributes

I have read the rails documents about the active record read and write
attributes.They says reading attributes have typecast automaticly
running behind.
But i wonder if this typecast works even the active record object has
not yet been saved to the database when reading attributes.
As for writing attributes,is there the typecast works behind even the
active record object has not yet been saved to the database?
If the controller receives the form data from user to construct an
active record object,all the params are string,should i manually cast
these strings to the corresponding type in the schema before making an
active record object and saving it? The automatic typecast works behind?

All the incoming params submitted from form have the string type value?
If i have a play_time attribute whose type is date,how do i save the
attribute as date type to the database when submitting form?I use
string.to_date to typecast before saving the attribute,but i fails.

please help me?

Guo Yangguang wrote: