1. DataSets Demystified

2. Who I am Shawn Wildermuth (swildermuth@adoguy.com) Senior Consultant with Magenic Technologies (http://www.magenic.com) C# MVP INETA Speaker Book Author –“Pragmatic ADO.NET”; –Co-author of “Programming SQL Server 2005” Editor of http://ONDotnet.com This Presentation can be found at: –http://adoguy.com/presentations

3. Overview What are DataSets DataAdapters DataTables DataSet Schema Updating DataSets Typed DataSets Better Business Objects

4. What are DataSets? Disconnected set of Database Data? In-Memory Database (IMDB)? Relational data with XML serialization? All three?

5. DataSet Structure

6. The DataAdapter Link Between the DataSet & the Database –Used to fill DataSets and update the database Contains Four Command Objects –SelectCommand –InsertCommand –UpdateCommand –DeleteCommand

7. DataAdapter and the DataSet System.Data DataSet System.Data.SqlClient SqlConnection SqlErrors SqlDataAdapter SqlDataReaderSqlCommand SqlParameter SqlParameters SqlError

8. using System; using System.Data; using System.Data.SqlClient; class HelloADONET { static void Main() { } SqlConnection conn = new SqlConnection("..."); SqlDataAdapter da = new SqlDataAdapter(); da.SelectCommand = conn.CreateCommand(); da.SelectCommand.CommandText = "SELECT * FROM AUTHORS"; DataSet dataSet = new DataSet(); da.Fill(dataSet); Hello DataSet !

9. DataTables Composed of –DataRows: Data –DataColumns: Schema DataTable tbl = dataSet.Tables["Customers"]; object name = tbl.Rows["CustomerID"]; string id = tbl.Rows["CompanyName"] as string; if (tbl.Columns["CustomerID"].DataType == typeof(int) ) { int name = tbl.Rows["CustomerID"] as int; }

10. DataRows Two possible versions of all data –RowState.Original –RowState.Modified –Changes stay in Modified until AcceptChanges or RejectChanges called

11. DataViews Window into a single DataTable Supports: –Sorting –Filtering DataView view = new DataView(dataSet.Tables[0]); view.Sort = "CompanyID"; view.RowFilter = "State = 'MA'";

12. DataSet Schema Composed of –DataColumns –Constraints –Relationships –Events (Triggers)

13. DataColumns Schema about a column –DataType –Maximum Size –IsNullable –Expressions Calculated Columns DataTable tbl = dataSet.Tables["Customers"]; // Expression Column tbl.Columns.Add("FullName", typeof(string), "LastName + ', ' + FirstName");

14. Constraints Rules about DataColumns –UniqueConstraint (like Primary Keys) –ForeignKeyConstraint DataTable tbl = dataSet.Tables["Customers"]; // Adds a unique constraint tbl.Columns["CustomerID"].Unique = true;

15. Relationships Navigable Link Between Tables –Adds a ForeignKeyConstraint DataColumn first = tblCustomers.Columns["CustomerID"]; DataColumn second = tblOrders.Columns["CustomerID"]; dataSet.Relations.Add(first, second); DataRows[] childRows = tblCustomers.Rows[0].GetChildRows(); int id = childRows[0]["OrderID"] as int;

16. Updating the Database DataAdapter to Update a DataTable –Update(DataSet) will update the database CommandBuilders –Creates Insert, Update & Delete Commands –Inefficient, but quick to prototyping SqlCommandBuilder bldr = new SqlCommandBuilder(dataAdapter); dataAdapter.Update(dataSet);

17. The Hard Part Disconnected Concurrency –Optimistic Concurrency Supported by CommandBuilders –Optimistic Concurrency could be more efficient –Pessimistic Concurrency can be achieved with Check-out, Check- in

18. Disconnected Concurrency The Hard-Part: –Optimistic Concurrency Supported by CommandBuilders (but inefficient) –Pessimistic Concurrency Can be achieved with custom Check-out/Check-in code –Destructive Concurrency Can only be handled by writing own update queries

19. Concurrency Methods Three Standard Methods –Timestamp –Comparison –Checksum

20. CommandBuilder Concurrency CommandBuilders –Allows updates and deletes where every field in the database is the same as when they were retrieved –Robust –Inefficient

21. CommandBuilder Sample DELETE FROM CUSTOMER WHERE ( (CustomerID = @p3) AND ((FirstName IS NULL AND @p4 IS NULL) OR (FirstName = @p5)) AND ((LastName IS NULL AND @p6 IS NULL) OR (LastName = @p7)) AND ((MiddleName IS NULL AND @p8 IS NULL) OR (MiddleName = @p9)) AND ((Address IS NULL AND @p10 IS NULL) OR (Address = @p11)) AND ((Apartment IS NULL AND @p12 IS NULL) OR (Apartment = @p13)) AND ((City IS NULL AND @p14 IS NULL) OR (City = @p15)) AND ((State IS NULL AND @p16 IS NULL) OR (State = @p17)) AND ((Zip IS NULL AND @p18 IS NULL) OR (Zip = @p19)) AND ((HomePhone IS NULL AND @p20 IS NULL) OR (HomePhone = @p21)) AND ((BusinessPhone IS NULL AND @p22 IS NULL) OR (BusinessPhone = @p23)) AND ((DOB IS NULL AND @p24 IS NULL) OR (DOB = @p25)) AND ((Discount IS NULL AND @p26 IS NULL) OR (Discount = @p27)) AND ((CheckedOut IS NULL AND @p28 IS NULL) OR (CheckedOut = @p29)) )

22. Custom Concurrency For SQL Server –To make it more efficient: use Timestamps DELETE FROM CUSTOMER WHERE (CustomerID = @p3) AND (Stamp = @p4) DataAdapter.DeleteCommand.CommandText!

23. Concurrency Violations DataAdapters throw DBConcurrencyException –This is thrown whenever the affected rows of an update is zero. –False positives are possible. DataAdapter.ContinueUpdateOnError –Each violated row will have errors associated with it. –DataRow.HasErrors will tell you which rows are problematic

24. Handling Concurrency Violations Three options: –Tell the user the data is stale, and offer to ‘freshen’ it and lose their changes –Ask the user if (s)he wants to overwrite needs to be done without a CommandBuilder –Field-level collision detection Allow field to be updated if it hasn’t changed

25. Typed DataSets Strong Typing XSD Based Schema Simple to setup schema –Relationships –Constraints –Keys Not good for amorphous data

26. Typed DataSet Structure

27. Type DataSet Demo

28. Improving Typed DataSets Typed DataSets support Annotations –Annotations improve usability of generated code –Types can be renamed Instead of CustomerTable, CustomerRow, how about Customer –Null Behavior can be changes Throws exception by default Returning empty or null references might be better

29. Annotations Annotations in the Typed DataSet XSD: –typedName: Specifies the name of an object. –typedPlural: Specifies the name of the collection of objects. typedParent: Specifies the name of the parent relationship. typedChildren: Specifies the name of the child relationship.

30. Annotations (2) Annotations in the Typed DataSet XSD: –nullValue: Specifies how to handle a DBNull value. Replacement Value: The value to return instead of a null –codegen:nullValue="" _throw: Throws an exception when the value is null –codegen:nullValue=_throw null: Returns a null reference. –If a value type is encountered an exception is thrown. empty: Returns a reference created with an empty constructor. –For strings, it returns String.Empty. For value types, an exception is thrown.

31. Practical Applications of DataSets Stop Writing Business Objects! –Derive from Typed DataSets –Let ADO.NET do the Database work –Write Just Your Business Logic –Deal with data as Relationally –or Hierarchically by using XmlDataDocument

32. Better Business Objects Using Typed DataSets –Strong Typing –XSD Based Schema –Simple to Setup relationships, constraints, etc. –Not very much use if you have amorphous data

33. Better Business Objects(2) Writing Business Objects normally involve three things: –Relational-to-Hierarchical Mapping –Data Access –Business Rules Traditional Business Objects –Set of classes –Strongly Typed

34. Better Business Objects (3) Writing Business Objects with Typed DataSets –Relational-to-Hierarchical Mapping for free –Data Access is handled by ADO.NET –Write your business rules and you’re done! Typed DataSet –ARE a set of classes –ARE Strongly Typed

35. Better Business Objects (4) Business Rules in Typed DataSets –Event Driven Catch OnRowChanging/OnRowChanged Events Handle Business Logic to ensure that rules are enforced –Derivation Derive from Typed DataSet Problems with Microsoft’s Generated code to allow this See http://adoguy.com/book/AGDataSetGenerator.aspx for a solution http://adoguy.com/book/AGDataSetGenerator.aspx

36. DataSets in Web Services Can you use DataSets in Web Services? –At first glance, the answer is no DataSets serialize to DiffGrams, DataSets DiffGrams are not platform agnostic Do not communicate the full schema –Would you want to use DataSets anyway? Great container for Structured XML Database integration Easy to intermingle database/XML data –When *not* to use DataSets When creating XML Documents from non-database sources

37. DataSets in Web Services (2) Possible Solutions? –DataSets can hold XML, so you can: return myDataSet.GetXml() –How about XmlDataDocument? return new XmlDataDocument(myDataSet)

38. Web Services and Schema DataSet schema is XSD! –When using DataSets, DocLiteral is your friend DataSets can define and be the holder for the documents that Web Services throw around –DataSet schema can define our WSDL Types Yassar Shohoud’s book shows you how “Real World XML Web Services”

39. Questions?