1. Neal Stublen nstublen@jccc.edu

2. Tonight’s Agenda  Interfaces  Generics  Code Organization  Databases  ADO.NET  Datasets  Q&A

4. What’s an interface?  It’s like a class with… No member data All methods are public All methods are abstract  An interface implies nothing about the implementation behind it  A class can only inherit from one class  A class can implement multiple interfaces Interfaces often represent only a portion of a class’ functionality

5. Why interfaces?  Interfaces are better suited to situations in which your applications require many unrelated object types to provide certain functionality  Interfaces are more flexible than base classes because you can define a single implementation that can implement multiple interfaces.  Interfaces are better in situations in which you do not want or need to inherit implementation from a base class.  Structures cannot inherit from classes, but they can implement interfaces.

6. Common.NET Interfaces  IComparable Used to compare two objects Sorting algorithms  IDisposable Frees unmanaged resources when an object goes out of scope  If your classes implement these interfaces, they can be used wherever these interfaces are specified

7. Example Interfaces public interface IStreamable { bool Read(FileStream inInput); bool Write(FileStream inOutput); } public interface IHTMLDisplayable { void Render(OutputStream inStream); }

8. Implementing Interfaces public interface IStreamable { bool Read(FileStream inInput); bool Write(FileStream inOutput); } public class MyObject : IStreamable { public bool Read(FileStream inInput) { } public bool Write(FileStream inOutput) { } }

9. Implementing ICloneable // Duplicate any cloneable object public List Duplicator(ICloneable src, int count) { List list = new List (); for (int index = 0; index < count; ++index) { list.Add(src.Clone()); } return list; }

10. Looking at IComparable  Any object that implements IComparable can be sorted with the generic Array.Sort() method

12. What’s a generic class?  A class definition that doesn’t explicitly declare all of the types it uses internally  Allows creation of new types by specifying those internal types later

13. Using Generic Types  Generic types are declared using <> after the type name Instead of the general purpose interface: IComparable Use the type-specific interface: IComparable class Temperature : IComparable

14. Generics Example class Average { public void Include(T inValue); public T Average { get {... } } Average integerAverage; Average doubleAverage;

15. Updating IComparable  Instead of comparing generic objects, we can compare Temperature objects

16. Common Generics  Collection classes List SortedList  Enumeration (foreach) IEnumerable IEnumerator

17. Generic Constraints public class MyGeneric where T: class { // T is a class (can be assigned null) } public class MyGeneric where T: class, IComparable { // T implements IComparable interface } public class MyGeneric where T: struct { // T is a struct } public class MyGeneric where T: new() { // T has a default constructor }

19. Code Organization  Multiple classes in a single file Closely related classes (e.g. EventArgs)  Nested classes Objects that only exist within the context of another type of object

20. Partial Classes  Split a single class over multiple files Forms split Designer code into separate file Possible to split interface implementations into separate files  Partial classes must have the same visibility  Partial methods split the declaration and implementation across files

21. Namespaces  Organize classes into logical groupings  Avoid type name collisions  using .

22. Nested Namespaces using ns1 { using ns2 { } } using ns1.ns2 { }

24. XML Documentation  Standardized documentation format for C# code  Type three slashes “///” before a method implementation or class member  tag is used by IntelliSense  Processed by third party tools Doxygen Sandcastle

26. Class Libraries  Share class across multiple projects  Projects “reference” other projects  Move SportsTeam into a class library

28. Databases  Client-server architecture One server, many clients Server runs Microsoft SQL Server Clients use ADO.NET 4  Relational databases SQL (Structured Query Language)

29. Tables  Tables store data  One or more records (rows)  A primary key uniquely identifies each row  Indexes provide an efficient way to access data based on values in specific columns

30. “Relations” Among Tables  Key columns are used to relate tables  Foreign keys in one table correspond to primary keys in another table One-to-many One-to-one Many-to-many

31. Table Columns  Columns are defined by a name and data type bit char, varchar, text datetime, smalldatetime decimal, numeric float, real bigint, int, smallint, tinyint money, smallmoney

32. Column Values  null (maybe, maybe not – depends on column definition)  Default value  Identity column (auto-increment)  Constraints

33. SELECT  Select data from a database SELECT column_name,column_name FROM table_name; SELECT * FROM table_name; SELECT title, publisher FROM books;

34. INNER JOIN  Select all rows from two table where specified columns have matching values SELECT column_name(s) FROM table1 INNER JOIN table2 ON table1.column_name=table2.column_name; SELECT column_name(s) FROM table1 JOIN table2 ON table1.column_name=table2.column_name;  INNER JOIN is the same as JOIN

35. ADD, UPDATE, DELETE  Add a row to a table INSERT INTO table_name VALUES (value1,value2,value3,...); INSERT INTO table_name (column1,column2,column3,...) VALUES (value1,value2,value3,...);  Update a row in a table UPDATE table_name SET column1=value1,column2=value2,... WHERE some_column=some_value;  Delete a row from a table DELETE FROM table_name WHERE some_column=some_value;

36. Online Reference  Tutorials and references http://w3schools.com/sql

38. ADO.NET  Data providers implement a common API to various database servers SQL Server OLE DB ODBC Oracle  Third party MySQL SQLite

39. Components  Database server .NET data provider Connection ○ Connects to a specific database Command ○ SELECT, UPDATE, etc. DataReader, DataAdapter ○ Help retrieve data from a query

40. Datasets  Store data in a disconnected cache  Data source may be a database, XML data, local application data  Mimics the structure and behavior of a relational database

41. Datasets Mimic Relational DB  Dataset contains a collection of tables Not necessarily the same table from the database May be a subset of columns and rows May be joined to another table  Tables contain a collection of columns  Tables contain a collection of rows  Tables contain a collection of constraints  Dataset contains a collection of relations  Everything is accessed through object properties

42. Alternatives to Datasets  You can use Command and Connection objects directly Select, Insert, Update, Delete

43. Database Concurrency  Multiple clients accessing data  ADO.NET datasets are “disconnected”  Pessimistic concurrency Lock database records to prevent conflicts  Optimistic concurrency Check for data changes before writing Throw an exception if data has changed  “Last in wins” Data is written by last operation Data may be lost

44. Avoid Concurrency Issues  Update and refresh datasets frequently  Avoid updating large tables in datasets  Only reduces risk! You still must handle the exceptions

47. Populating a Database  SQLExpress should be installed with Visual Studio  The book provides a.sql file for populating the MMABooks database in SQLExpress  Double-click the.bat file on the S: drive  We’ll need to repeat this process at the start of each class session

48. Confirm Database Access  Using Visual Studio to locate the new database as a Data Source View > Server Explorer Add Connection... Server name:.\SQLEXPRESS Database name: MMABooks Test Connection

49. Using the Data Sources Window

50. Dataset Summary  Instead of a database, we can pull data from: WCF Data Services Custom objects SharePoint  Entity Framework Object-relational mapping framework (ORM) Maps database table data to C# objects ○ Object instance represents a table row  View > Server Explorer

51. Dataset Summary  Connection strings can be stored in app.config  Allows reuse of the connection string  A dataset can be modified in Visual Studio to add tables, columns, etc.  Visual Studio generates.xsd schema files for the dataset

53. DataGridView Control  Bound control  Table view of the dataset  Multiple objects are added to the form

54. Other Bound Controls  Change default data control for table in Data Sources  Change default data control for columns in Data Sources

55. Behind the Scenes…  Load event is updated for the form  Save click event is updated for the binding navigator

56. Bound TextBox Controls  Formatting and Advanced Binding  Select TextBox  Open Properties Window  Expand DataBindings property  Select Advanced option, click “…”  Select new format type  Specify representation of null value

57. Bound ComboBox Controls  Populate a ComboBox with values from a column of a database table  SelectedItem is used to specify the value in a column of another database table

58. Code Practice  Select customer state using dropdown list ComboBox instead of TextBox  Create StatesDataSet in Data Source window  Add DataSet control for StatesDataSet and set DataSetName property  Add BindingSource control for DataSet and set DataSource/DataMember properties  Set State field to use ComboBox  Set ComboBox to use data bound controls  Clear ComboBox data bindings for Text property