June 2019
Beginner to intermediate
770 pages
19h 24m
English
Content preview from Mastering Object-Oriented Python - Second Edition
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Schema evolution
When working with an SQL database, we have to address the problem of schema evolution. Our objects have a dynamic state and a (relatively) static class definition. We can easily persist the dynamic state of an object. Our class defines the schema for the persistent data. The ORM provides mappings from our class to an SQL implementation.
When we change a class definition, how can we fetch objects from the database? If the database must change, how do we upgrade the Python mappings and still access the data? A good design often involves some combination of several techniques.
The changes to the methods and properties of a Python class will not change the mapping to the SQL rows. These can be termed minor changes, as the tables ...
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