leading zeros in rails

It'd be better to store it as an integer and just display it as you described on runtime. Every language has its own way to pad zeros - for Ruby you can use String#rjust. This method pads a string (right-justified) so that it becomes a given length, using a given padding character.

str.rjust(integer, padstr=' ') → new_str

If integer is greater than the length of str, returns a new String of length integer with str right justified and padded with padstr; otherwise, returns str.

some_int = 5
some_int.to_s.rjust(2, '0')  # => '05'
some_int.to_s.rjust(5, '0')  # => '00005'

another_int = 150
another_int.to_s.rjust(2, '0') # => '150'
another_int.to_s.rjust(3, '0') # => '150'
another_int.to_s.rjust(5, '0') # => '00150'

You can transform the integer into a string of that kind with:

result_string = '%02i' % your_integer

This is independent from how it gets saved in the db.

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This is also quite handy:

"%.2d" % integer

The resultant string will be of 2 characters and if the number is of less than 2 characters, then 0s will be present in the string