Database refactoring

For the beginning…•Avoid overspecialization

Application developer Database developer

Developer Developer

CommunicationCooperationExchange of experience

Barrier

Definition

•Refactoring of databases is the database schema change, improving its design, but not affecting its behavioral and information semantics.

•It contains both structural and functional aspects

What can we refactor in DB?

DB keeps:• Data (are kept according to the scheme)• Stored code

The stored code doesn’t differ from any other code (it should be tested)

The scheme of data (tables, indexes, etc.)

The availability of data complicates the refactoring of the scheme!

Why should we refactor?

• Correct the inherited database

• Ensure the evolutionary development

• Prevent the redundant design (over-design)

Smells of bad code in database

All the smells of codes can be applied to the stored code including:

• Procedures-monsters• Spaghetti code• Code duplication• Oversaturation of the conditional operators• etc.

Smells characteristic for DB:• Table/column of wide destination• Redundant data (repeated in several tables)• Table with a huge number of columns/rows• Smart columns (xml)• Lack of limitations (lack of validation)• Fear of changes in data scheme or procedure

Fear of changes

•The most «stinking» smell•Prevents the development•Reduces the effectiveness•Suggests an even bigger mess•Over time it becomes only worse

How to proceed?

•Create your sandbox of development•Transfer changes in the sandbox of

integration•Introduce in production

Sandboxes

Frequent deployment Controlled deployment

Highly controlled deployment

The best case (the easiest)

Worst case (the most complex)

Trivial things

•Is it possible to rename a column in the database without changing the hundreds of applications?

•If we can not make such a triviality as we can do something really serious?

Unit tests in the database

•Is it too difficult?•Isn’t there a good testing tool

(framework)?

Running unit tests

•Anonymous PL/SQL code•No need to change the database•Call raise_application_error a specific

communication in case of an error•A rollback at the end of the test•Launch any SQL tools

Example of a test

Logs changes (changelog)

•You must track changes•Writing delta-scripts (migration):

▫At the beginning of the transition period▫At the end of the transition period

•The same scripts for▫Update sandboxes▫Deployment on the production

Simple script

Versioning

Teamwork

•Developers▫Close cooperation with DB administrators▫Skills of operation with databases

•Administrators of DB and designers of DB▫Should be involved in developing the

application▫Skills of application development

Testing tools

•Delta-scripts▫Dbdeploy, liquibase, deltasql▫It's easy to write yourself

•PL/SQL code, Oracle SQL Devepoler, Intellij IDEA

Categories of database refactorings

Category Description Example

Refactoring of operation structures

Changes in the definition of one or more tables

Move a column from one table to another, or break the multipurpose column on theseveral separate columns, each of which performs the individual assignment

Refactorings of data quality

Changes that can improve the quality of information stored in the database

Creating a column that does not allow NULL values, to ensure that there are always meaningful values

Categories of database refactoringsCategory Description Example

Refactorings of referential integrity

The changes, which ensure that the referenced string exists in another table, and allow properly removing this string which are not needed

Adding a trigger to realize the rule of a cascading delete, covering the two entities, to replace the code which before was implemented outside the database

Refactorings of architecture

Changes contributing to the improvement of interaction between external programs with database

Replacement of the existing procedures in the Java language which code is in a shared library code, with the stored procedure, which are in the database. After the code is implemented in the form of stored procedures, you can use this code in an application other than Java

Categories of database refactorings

Category Description Example

Refactoring of methods

Changes in the method (stored procedure, stored function or trigger), which contribute to the improvement of its quality. To the methods of the database we can apply many of the refactorings of code

Rename the stored procedure in order to simplify the understanding of its purpose

Conversion other than refactorings

Changes in the database schema, which lead to change in its semantics

Adding a new column to an existing table