1. Building a Testable Data Access Layer
Visual Studio Live Orlando 2010MGB 2003
Building a Testable Data Access Layer
Todd Anglin
Chief Evangelist, Telerik
Level: Intermediate
© 2003 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

2. Introductions Chief Evangelist, Telerik Todd Anglin Microsoft MVP
ASP Insider
President NHDNUG & O’Reilly Author
TelerikWatch.com
@toddanglin

3. Testing Data Operations
Define “Data Layer”
Data Layer Options
Build Data Layer
Testing Data Operations
today’s plan

4. what is a “data layer”?

5. Domain Logic (“the code that makes you money”)
Data Layer
Responsible for talking to “persistence layer”
Presentation
Web
Desktop
Service
Domain Logic (“the code that makes you money”)
Data / Model
Persistence
Database
Cloud
XML
Etc.

6. why build a data layer?
what’s the benefit?

7. importance of data layer
Decouple application from persistence
= easier maintenance
= improved testability
= greater reusability

8. Domain Logic (“the code that makes you money”)
Presentation
Web
Desktop
Service
Domain Logic (“the code that makes you money”)
Data
Persistence
Database
Cloud
XML
Etc.

9. a good data layer…

10. Handles all data access Hides implementation Flexible
Easy to refactor

11. a bad data layer is…

12. Does not centralize data access
Makes application very dependent on persistent store
Easy*
Easy = Easy to build if you’re not careful

13. how do we build “data layers”?

14. By Hand
Pros
POCO
YAGNI
No-RTFM
Cons
Time
No FM
ORM
Pros
Time
Flexible
Cons
Learning
Limits
Trust*

15. popular .NET ORMs Microsoft LinqToSQL Entity Framework Open Source
nHibernate
Commercial
Telerik OpenAccess
LLBGenPro
EntitySpaces

16. Build data layer with LinqToSql & EF & OpenAccess
Demo

17. data layer patterns Domain Driven Design (DDD) ActiveRecord
Key concepts: Repositories act on model
ActiveRecord
Key concepts: Model objects act on themselves
Data Mapper
Key concepts: Objects mapped to tables

18. Add data access pattern to project
Demo

19. testing the data layer Everything is familiar up to this point.
Now the dreaded step may of us avoid: Creating tests for the data layer

20. A B two testing camps Test Database Mock Database Concepts: Concepts:
Test against “real” database
Use set-up/tear-down code to create test data
Good When…
You put lots of logic in your database
Concepts:
Test against “fake” database
Isolates your code from database behavior
Good When…
You want fast unit tests and you put most logic in code

21. picking a camp “Test” Database Mocking Pros Pros Cons Cons Unit test
Isolate concerns
Fast
Cons
“Hides” issues
Does not test database logic
“Test” Database
Pros
Catches more issues
Familiar
Cons
Slow
Not a “unit” test
Hides issues example = concurrency, auto-gen DB values, etc.

22. testing considerations
What is a unit test?
What are other types of testing?

23. UNIT TEST INTEGRATION TEST FUNCTIONAL TEST
“Isolated. Repeatable. Fast.”
INTEGRATION TEST
“Test interaction between units.”
FUNCTIONAL TEST
“Test behavior from user perspective.”

24. Database Communication (ORM, ADO.NET, etc.)
mock testing
Goal: Test your business logic
UI Behaviors
Services
Business Code
Repository
Database Communication (ORM, ADO.NET, etc.)
Database

25. mocking Stunt doubles for real objects Look the same on the outside
Mocking Tools:
JustMock (by Telerik)
Isolator (by TypeMock)
MOQ (OSS)
RhinoMocks (OSS)

26. AAA mocking pattern
//Arrange Set-up your test variables and mocks //Act Execute your code like normal //Assert Verify what happened

27. DEMO: MOCKING DATABASE
Testing L2S with Mock Objects
DEMO: MOCKING DATABASE

28. A Steps for every test: test database
Goal: Test your business logic + database behavior
Steps for every test:
Create database schema + test data
(Optional) Test database setup correctly
Execute unit test code
Verify database behaved correctly

29. hard parts Creating test schema/data Speed DbUnit In memory database
SQL Lite, SQL CE, etc.

30. rules for test database tests
Prior to running tests, schema should be redeployed to test DB (+ test data)
Tests should not change existing data
Edits, Deletes should be on records created by test
Original data should be read-only
Tests should not depend on changes from previous tests

31. DEMO: TESTinG with real DB
Creating integration tests to talk to real database
DEMO: TESTinG with real DB

32. should you test your DAL?

33. Q&A
@toddanglin
telerikwatch.com

34. Links
4GuysFromRolla on Testing DAL (2005)
Unit Testing the DAL (Java, but great discussion of DAL data testing)
Roy Osherove on using Mocks for DAL testing
SQL Lite project page
System.Data.SQLite:
DbUnit.NET (last updated 2006 – still alpha)
SQL Server Compact 4 CTP1 (2010)
SQL Script to clear all tables in database
Microsoft.SqlServer.Management.Smo primer
Multi-tier L2S architecture ideas