1 / 20

Introductions…

Generic Data Access in Microsoft .NET: a Compelling Example of Inheritance, Interfaces, and the Factory Method Design Pattern OOPSLA 2004 : Design Patterns and Objects First Workshop Joe Hummel, PhD Dept of Math/CS Lake Forest College hummel@lakeforest.edu. Introductions…. Joe Hummel, PhD

etana
Download Presentation

Introductions…

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Generic Data Access in Microsoft .NET: aCompelling Example of Inheritance, Interfaces,and the Factory Method Design PatternOOPSLA 2004 : Design Patterns and Objects First WorkshopJoe Hummel, PhDDept of Math/CSLake Forest Collegehummel@lakeforest.edu

  2. Introductions… • Joe Hummel, PhD • Chicago, USA • email: hummel@lakeforest.edu • web: www.lakeforest.edu/~hummel • I wear 2 hats: • Academic: • Associate Prof. of CS at Lake Forest College (www.lakeforest.edu) • PhD from UC-Irvine (Optimizing Compilers, 1998) • Industry: • professional trainer (1-5 day workshops, webcasts, conferences) • specializing in Microsoft Windows development

  3. Part 1 • The problem…

  4. Database access in .NET is vendor-specific • A different set of classes for each technology: • ODBC • OLEDB • SQL Server • Oracle • DB2 • … • Saving grace: • Each set of classes is based on a common design: • Connection object to open connection with DB • Command object for executing SQL • DataReader object for reading records • etc. DB

  5. Naïve result • Developers create a distinct class for each DB type: SQLServerDB MSAccessDB OracleDB MySQLDB

  6. Goal • Apply good OOD to obtain reusable, maintainable result: GenericDataAccess MSAccessDB SQLServerDB OracleDB MySQLDB

  7. Killer example? • Real • Important • Inheritance • Interfaces • Factory Method design pattern

  8. Part 2 • From naïve to gOOd solution…

  9. Outline • 4-step process: • identify generic vs. vendor-specific data access code • apply Factory Method design pattern • use interfaces to define common design across Microsoft’s classes • use inheritance to: • ensure our generic & concrete data access classes integrate properly • enable single, polymorphic access to different types of databases GenericDataAccess db; db = new ConcreteDataAccessClass(…); db.Insert(…); db.Update(…);

  10. Step 1 SQL Server • Identify generic vs. vendor-specific… System.Data.SqlClient.SqlConnection conn; System.Data.SqlClient.SqlCommand cmd; System.Data.SqlClient.SqlDataReader reader; conn = new System.Data.SqlClient.SqlConnection(“connection info…”); cmd = new System.Data.SqlClient.SqlCommand(“Select * …”, conn); conn.Open(); // open connection to DB reader = cmd.ExecuteReader(); // execute SQL and return object for accessing DB… while ( reader.Read() ) // for each record… { . . . } conn.Close();

  11. Step 2 • Apply Factory Method design pattern… ??? conn; ??? cmd; ??? reader; conn = CreateConnection(“connection info…”); cmd = CreateCommand(“Select * …”, conn); conn.Open(); // open connection to DB reader = cmd.ExecuteReader(); // execute SQL and return object for accessing DB… while ( reader.Read() ) // for each record… { . . . } conn.Close(); private ??? CreateConnection(string connectInfo) { return new System.Data.SqlClient.SqlConnection(connectInfo); } . . .

  12. Step 3 • Use interfaces to define common design across DB classes… System.Data.IDbConnection conn; System.Data.IDbCommand cmd; System.Data.IDataReader reader; conn = CreateConnection(“connection info…”); cmd = CreateCommand(“Select * …”, conn); conn.Open(); // open connection to DB reader = cmd.ExecuteReader(); // execute SQL and return object for accessing DB… while ( reader.Read() ) // for each record… { . . . } conn.Close(); private IDbConnection CreateConnection(string connectInfo) { return new System.Data.SqlClient.SqlConnection(connectInfo); } . . .

  13. Step 4 • Use inheritance & abstract base class to enforce design… public abstract class GenericDataAccess { public void Insert(…) { … } public void Update(…) { … } protected abstract IDbConnection CreateConnection(string info); protected abstract IDbCommand CreateCommand(string SQL, IDbConnection conn); } public class SQLServerDB : GenericDataAccess { protected IDbConnection CreateConnection(string info) { return new System.Data.SqlClient.SqlConnection(info); } . . .

  14. GenericDataAccess MSAccessDB SQLServerDB OracleDB End result? • Reusable, maintainable data access hierarchy! • Single, polymorphic database access! GenericDataAccess db1, db2, db3; db1 = new SQLServerDB(…); db2 = new MSAccessDB(…); db3 = new OracleDB(…); db1.Insert(…); db2.Update(…); db3.Delete(…);

  15. Part 3 • Extensions…

  16. Possible extensions • Specialized exception handling: • different databases respond differently to error conditions • define generic exception handler in base class • derived classes can override & specialize if desired • Template Method design pattern • Data access code in .NET really consists of 2 levels: • low-level code that performs database access: • execute Action query (insert, update, delete) • server-side Select query • client-side Select query • high-level code for domain-specific stuff: validation, build SQL, etc. • redesign data access hierarchy to take this into account…

  17. Other possible extensions • (These are from the workshop discussion…) • Abstract Factory pattern: • derived classes are really producing objects from a family of classes • should recognize this via Abstract Factory pattern • Configuration pattern: • make system more dynamic by reading class names from a file • apply Configuration pattern

  18. TxtReader HtmlReader XmlReader .txt .html .xml Application in CS1 / CS2? • Perhaps a similar problem involving files instead of DBs… • we give students a set of classes for reading / writing text files • they apply 4 steps outlined earlier

  19. ASTNode Stmt Expr While Assign If Binary Literal Other ideas for CS1 / CS2 • I’ve used the following successfully in CS1 / CS2 sequence: • compilers use AST as an internal representation • AST (abstract syntax tree) involves: • non-trivial inheritance hierarchy • Visitor design pattern • I had students build a recursive-descent parser • I provided lexer • they designed AST & built parser

  20. That's it! • Questions? • Discussion? • Thank you!

More Related