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 @toddanglin TelerikWatch.com

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

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

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

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

Handles all data access Hides implementation Flexible Easy to refactor

Does not centralize data access Makes application very dependent on persistent store Easy*

how do we build “data layers”?

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

DEMO Build data layer with LinqToSql & EF & OpenAccess

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

DEMO Add data access pattern to project

two testing camps 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 A Test Database B Mock Database

picking a camp Mocking Pros 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

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

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

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

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

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

DEMO: MOCKING DATABASE Testing L2S with Mock Objects

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

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

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

DEMO: TESTING WITH REAL DB Creating integration tests to talk to real database

[email_address] @toddanglin telerikwatch.com Q & A

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/

Building a Testable Data Access Layer

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