One of the many jobs of a Table object is to validate the data
before it's written to the database. This is done in its
check() method.
You can override that method in your custom Table classes to add custom validation. At the very least you should validate the data type and that the data is within an accepted range of values. The latter is domain-specific, i.e. you need to know how your database table and component work to write that code. That's why Joomla doesn't offer much in the way of automatic data validation.