Taming the Database
Harry Cummings, Softwire
Taming the Database
- Maintainability
- Testability
- Performance
Motivation
- Implementation
- Deployment
- Architecture
Overview
Implementation
Testing
- Runs in-process
- Can run in-memory
- Available via NuGet
Lightweight Databases
- Runs in-process/memory
- Compatibility modes
- Available via Maven
SQLite
H2
- Requires a file
- Close-ish to SQL Server
- Now in end-of-life
SQL Server Compact
- Requires installation
- More heavyweight
- Very close to SQL Server
SQL Server Express
- Fast!
- Easy to isolate
- Can't really test...
- Persistence
- Transactionality
- Complex querying
Testing approaches
- Fast but not unit-test-fast
- Easy to isolate
- Reasonably realistic
- May be subtle differences
- ORMs can help with this
Faking the library
In-process DB
- Slow
- Very realistic
- Large setup overhead
- Isolation requires care
Separate instance
- Slow
- Completely realistic
- Isolation is challenging
Shared instance
Testing Approaches
Faking the library
In-process DB
Isolated real DB
Shared database
Deployment
Change management
Recreate and seed
- Easy to autogenerate
- Data-destroying
Incremental migration
- Hard to autogenerate
- Data preserving?
- Up/down vs. forward only
Deployment
Breaking changes
Database first
- Deploy back-compatible DB change
- Deploy application
- Remove old DB functionality
Application first
- Deploy back-compatible app change
- Deploy database
- Remove old app functionality
Architecture
Architecture
- Attempts to achieve separation of concerns
- Actually makes SRP difficult
- Can make the database the foundation
- Encourages using the DB as an integration point
Presentation
Logic
Data
Traditional 3-layer architecture
Architecture
- Puts business logic at the core of the application
- Treats the database as a collaborator
- Discourages leaky persistence abstraction
- Makes APIs the integration point
Ports and Adapters ('Hexagonal')
Adaptors
Ports
Core
Architecture
- True separation of persistence concerns
- Events are immutable, other data transient
- Aids performance and scalability
- Reduces need for schema migration
- Very flexible and loosely coupled
Event Sourcing / Stream Processing
Application
Raw
Aggr.
Summary
ORMs
Tests
Change
Structure
Moderation
Use cases
Performance
Variety
Isolation
Realism
Compatibility
Existing data
Data flow
App core
Taming the Database
?
Taming the Database
By hgcummings
Taming the Database
SDD Conf 2015
