This document provides an overview of using Object Relational Mapping (ORM) with Python SQLAlchemy and MariaSQL. It discusses using ORM for database access, mapping database tables to Python classes, querying relationships between tables, and more advanced topics like adding virtual columns without changing the database schema. The document also includes examples of querying data from multiple related tables and creating database views using alembic migrations.

1. ORM
Based on SQLAlchemy & MariaSQL
- cmj @ HST

2. Outline
• ORM - Object Relational Mapping
• Python - SQLAlchemy
• MariaSQL-10.3.12 on Mac OS X

3. Conclusion
• Using raw SQL if you BE GOOD AT SQL
• If you have NOT GOOD team members, using ORM

4. Philosophy
• OOP - Object-Oriented Programming
• Abstract
• Portable

5. Testing Environment
• Using pyenv + pipenv
• alembic
• sqlalchemy
• pymysql
https://blog.steven5538.tw/2018/05/13/use-pyenv-pipenv-in-your-project/

6. alembic
Initialization

7. Table Mapping
• Table
• Create
• Reflecting

8. Create Table

9. Create By SQLAlchemy

10. Create
• Inherit by Base - declarative_base
• Column ( type, **kwargs )
• primary_key
• server_default
• default
• nullable
• Index
• … etc

11. Reflecting
• Table('demo', Base.metadata, autoload=True)

12. SQL to ORM

13. SQL Command
• Query (SELECT)
• WHERE
• JOIN-ON
• GROUP BY - HAVING
• ORDER BY
• LIMIT / OFFSET

14. Query

15. Relation
• NOTE - Two databases has relation if
1. Foreign Key ?
2. Same column name ?

16. Foreign Key
• ForeignKey
• Same type / table name and column name
• relationship
• Table name
• one-to-one / one-to-many / many-to-one
• Many-to-may

17. SQL Joins

18. Relationship

19. OOP / ORM
relationship

20. Query with JOIN
• JOIN table
• join
• isouter=False
• full=False
• outerjoing - create a left outer join

22. Dump ORM
• Using statement and compile
• show the raw SQL
• dump as string

23. Advanced

24. ORM Benefit
• DO NOT WANT change the DB schema
• HAVE TO change the column name
• @hybrid_property

25. Column Name

26. Change in ORM-Level
• ALTER table is expensive
• Change the source code
• Keep DB schema

27. More Flexibility
• Wrapper the response
• Reduce DB schema
• Hack in ORM

28. Advanced Hybrid
• Simple manufacture
• Most Py builtin methods

29. Be PRO

30. Example

31. DB Schema
• Three table
• hacker and sheep are simple table
• pwned is many-to-many relation

32. Question 1
• How to QUERY
• All sheep pwned by hacker Steven
• All sheep NOT pwned by hacker Steven

33. Pwned

34. NOT Pwned

35. Question 2
• How to QUERY max …
• Max pwned server

36. Max pwned

37. Question 3
• Hacked in ORM
• Add virtual column in ORM, not change DB schema
• Change column name but not change DB schema

38. Virtual Column

39. Question 4
• Migrate data
• Using new column if valid, or using old column

41. Request from Steven

42. How to Create VIEW
• By alembic
• Ref : alembic cookbook
https://alembic.sqlalchemy.org/en/latest/cookbook.html#replaceable-objects

43. Code : alembic

44. VIEW

45. Query VIEW
• Using reflecting table
• Using __table__ and __mapper_args__ to map
reflecting table

47. No Q&A