DataSets Demystified

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

Overview

• What are DataSets• DataAdapters• DataTables• DataSet Schema• Updating DataSets• Typed DataSets• Better Business Objects

What are DataSets?

• Disconnected set of Database Data?• In-Memory Database (IMDB)?• Relational data with XML serialization?• All three?

DataSet Structure

Legend

DataSet

DataRow DataColumn

Constraint DataRelation

DataTable

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.NETClass

Composition

The DataAdapter

• Link Between the DataSet & the Database– Used to fill DataSets and update the database

• Contains Four Command Objects– SelectCommand– InsertCommand– UpdateCommand– DeleteCommand

DataAdapter and the DataSetSystem.Data

DataSet

System.Data.SqlClient

SqlConnection

SqlErrors

SqlDataAdapter

SqlDataReaderSqlCommand

SqlParameter

SqlParameters

SqlError

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!

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;}

DataRows

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

called

DataViews

• Window into a single DataTable• Supports:

– Sorting– Filtering

DataView view = new DataView(dataSet.Tables[0]);

view.Sort = "CompanyID";view.RowFilter = "State = 'MA'";

DataSet Schema

• Composed of– DataColumns– Constraints– Relationships– Events (Triggers)

DataColumns

• Schema about a column– DataType– Maximum Size– IsNullable– Expressions

• Calculated Columns

DataTable tbl = dataSet.Tables["Customers"];

// Expression Columntbl.Columns.Add("FullName", typeof(string), "LastName + ', ' + FirstName");

Constraints

• Rules about DataColumns– UniqueConstraint (like Primary Keys)– ForeignKeyConstraint

DataTable tbl = dataSet.Tables["Customers"];

// Adds a unique constrainttbl.Columns["CustomerID"].Unique = true;

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;

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);

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

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

Concurrency Methods

• Three Standard Methods– Timestamp– Comparison– Checksum

CommandBuilder Concurrency

• CommandBuilders– Allows updates and deletes where every field in the database is the

same as when they were retrieved– Robust– Inefficient

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)) )

Custom Concurrency

• For SQL Server– To make it more efficient: use Timestamps

• DELETE FROM CUSTOMER WHERE (CustomerID = @p3) AND (Stamp = @p4)

• DataAdapter.DeleteCommand.CommandText!

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

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

Typed DataSets

• Strong Typing• XSD Based Schema• Simple to setup schema

– Relationships– Constraints– Keys

• Not good for amorphous data

Typed DataSet Structure

DataSet

DataRow DataColumn

Constraint DataRelation

DataTable

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TypedDataSet

Customers

CustomerRow CustomerIDColumn

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Composition

Generalization

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Type DataSet Demo

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

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.

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.

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

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

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

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

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

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

DataSets in Web Services (2)

• Possible Solutions?– DataSets can hold XML, so you can:

• return myDataSet.GetXml()– How about XmlDataDocument?

• return new XmlDataDocument(myDataSet)

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”

Questions?