1. Database Keys and Constraints

2. What? A database is for storing information.
It is comprised of tables, views and other entities.
Each entity has “columns”, and can store “rows” of data.

3. Constraints
For maintaining data integrity.
Yup.

4. Constraints
Primary Keys
Unique Keys
Foreign Keys

5. Primary Keys Sequences AUTO_INCREMENT in MySQL. IDENTITY in MSSQL.
Sequences (independent entities, not column attributes) in PostgreSQL, Oracle. id
INT(11)
title
VARCHAR(255)
content
TEXT
slug

6. Primary Keys Natural Keys email VARCHAR(255) interests TEXT location
likes_plums
TINYINT(1)

7. Primary Keys Natural Keys lang_code VARCHAR(100) fte_app_id INT(11)
text
TEXT
likes_apricots
TINYINT(1)

8. Unique Keys Forces, well... uniqueness across all rows in a table. id
INT(11)
VARCHAR(255)
location
likes_anchovies
TINYINT(1)

9. Foreign Keys “Relationships”. id INT(11) email VARCHAR(255) location
likes_anchovies
TINYINT(1) id
INT(11)
user_id
title
VARCHAR(255)
comment
TEXT

10. Foreign Keys
Enforces integrity at all times; no comments record can exist without a corresponding user record. id
INT(11)
VARCHAR(255)
location
likes_anchovies
TINYINT(1) id
INT(11)
user_id
title
VARCHAR(255)
comment
TEXT

11. Foreign Keys
When deleting and updating a “parent” table, we can choose how “child” rows will react.
CASCADE
RESTRICT
SET NULL
SET DEFAULT (Broken in MySQL)

12. Why Foreign Keys? Consistency.
No broken relationships, eg. child rows without parents.
Putting these checks in the database ensure that, no matter what tool is being used, or if that tool is buggy or not, consistency is maintained.

13. Why Foreign Keys? Discoverability That's not even a word, man.
Define the relationship in the DB, and tools other than VanillaCMS can use the relationships.
eg. other PHP apps, general MySQL clients, RedMine, RecordFerry, etc.
At present, you either need to include the entirety of the CMS to discover the relationships, or try to break out the code that handles them.

14. Downsides No “God Tables”
(“Generic” Tables that store many types of things with many types of column.)
ie. gen_content_item has:
ncci_id
ncci_class (type)
ncci_flag1
ncci_flag2
ncci_text1
ncci_text2
ncci_fkey1

15. Downsides
There's no way to enforce any sort of constraints on something that will have different rules depending on the value of “ncci_class”.
No conditional foreign keys.
ncci_varchar1 may be an address today, or someone's lunch-order tomorrow.

17. Soft-Deletion
Mark a row as “deleted” without removing it from its table.
… And therefore keeping relationships intact, and a discoverable record of activity.
Retrieve active records (by default) with “deleted = 0”. id
INT(11)
VARCHAR(255)
location
deleted
INT(11) DEFAULT 0

18. Soft-Deletion Example
PRIMARY id
location
deleted 1
Down the side of the couch. 2
Neither here nor there.

19. Soft-Deletion Example
PRIMARY id
location
deleted 1
Down the side of the couch. 2
Neither here nor there.

20. Soft-Deletion Example
PRIMARY id
location
deleted 1
Down the side of the couch. 2
Neither here nor there.

21. Soft-Deletion + Uniqueness
Bring our uniqueness constraint back in.
How do we keep addresses unique when we have soft-deleted records hanging around? id
INT(11)
VARCHAR(255)
location
deleted
INT(11) DEFAULT 0

22. Soft-Deletion Example
PRIMARY
UNIQUE id
location
deleted 1
Down the side of the couch. 2
Neither here nor there.

23. Soft-Deletion Example
PRIMARY
UNIQUE id
location
deleted 1
Down the side of the couch. 2
Neither here nor there. 3
Over here. 4
Over there.

24. Soft-Deletion + Uniqueness
Put the uniqueness constraint on and deleted. id
INT(11)
VARCHAR(255)
location
deleted
INT(11) DEFAULT 0

25. Soft-Deletion + Uniqueness
When soft-deleting a record, copy its ID to the deleted field.
Any “deleted = 0” queries will not pick it up.
Only one “active” record allowed with that address at one time. id
INT(11)
VARCHAR(255)
location
deleted
INT(11) DEFAULT 0

26. Soft-Deletion Example
PRIMARY
UNIQUE id
location
deleted 1
Down the side of the couch. 2
Neither here nor there.

27. Soft-Deletion Example
PRIMARY
UNIQUE id
location
deleted 1
Down the side of the couch. 2
Neither here nor there.

28. Soft-Deletion Example
PRIMARY
UNIQUE id
location
deleted 1
Down the side of the couch. 2
Neither here nor there.

29. Soft-Deletion Example
PRIMARY
UNIQUE id
location
deleted 1
Down the side of the couch. 2
Neither here nor there. 3
Over here.

30. Soft-Deletion Example
PRIMARY
UNIQUE id
location
deleted 1
Down the side of the couch. 2
Neither here nor there. 3
Over here. 4
Over there.

31. Gooooooo Planet! Users with auto-incrementing ID.
Unique addresses.
Comments that are always associated with a user.
Records of deleted users and comments. id
INT(11)
VARCHAR(255)
location
deleted
INT(11) DEFAULT 0 id
INT(11)
user_id
comment
TEXT
deleted
INT(11) DEFAULT 0

32. NO UNICORNS TODAY