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Building a Testable Data Access Layer

Building a Testable Data Access Layer. Todd Anglin Chief Evangelist, Telerik. Level: Intermediate. Introductions. Todd Anglin Chief Evangelist, Telerik Microsoft MVP ASP Insider President NHDNUG & O’Reilly Author. TelerikWatch.com. @toddanglin. today’s plan. what is a “data layer”?.

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Building a Testable Data Access Layer

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  1. Building a Testable Data Access Layer Todd Anglin Chief Evangelist, Telerik Level: Intermediate

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

  3. today’s plan

  4. what is a “data layer”?

  5. 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. 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*

  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

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

  17. data layer patterns • Domain Driven Design (DDD) • 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

  20. two testing camps A B Test Database Mock Database • 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. “Test” Database • Pros • Catches more issues • Familiar • Cons • Slow • Not a “unit” test • Mocking • Pros • Unit test • Isolate concerns • Fast • Cons • “Hides” issues • Does not test database logic picking a camp

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

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

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

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

  26. Testing L2S with Mock Objects DEMO: MOCKING DATABASE

  27. A 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

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

  29. 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

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

  31. should you test your DAL?

  32. Q&A anglin@telerik.com @toddanglin telerikwatch.com

  33. Links • 4GuysFromRolla on Testing DAL (2005) • http://aspnet.4guysfromrolla.com/articles/040605-1.2.aspx • Unit Testing the DAL (Java, but great discussion of DAL data testing) • http://www.buunguyen.net/blog/unit-testing-the-data-access-layer.html • Roy Osherove on using Mocks for DAL testing • http://weblogs.asp.net/rosherove/archive/2003/09/30/29734.aspx • SQL Lite project page • http://www.sqlite.org/docs.html • System.Data.SQLite: http://sqlite.phxsoftware.com/ • http://www.mikeduncan.com/sqlite-on-dotnet-in-3-mins/ • http://hendryluk.wordpress.com/2008/10/07/data-access-test-with-sqlite/ • DbUnit.NET (last updated 2006 – still alpha) • http://dbunit-net.sourceforge.net/GettingStarted.html • SQL Server Compact 4 CTP1 (2010) • http://www.microsoft.com/downloads/details.aspx?FamilyID=0d2357ea-324f-46fd-88fc-7364c80e4fdb&displaylang=en • http://robtiffany.com/sql-server-compact/here-comes-sql-server-compact-4-0 • SQL Script to clear all tables in database • http://www.smallworkarounds.net/2009/02/script-to-delete-all-data-from-sql.html • Microsoft.SqlServer.Management.Smo primer • http://davidhayden.com/blog/dave/archive/2006/01/27/2774.aspx • http://social.msdn.microsoft.com/Forums/en-US/adodotnetdataproviders/thread/43e8bc3a-1132-453b-b950-09427e970f31 • Multi-tier L2S architecture ideas • http://blog.stevensanderson.com/2007/11/29/linq-to-sql-the-multi-tier-story/

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