1. Databases and Data Access
Mark Sapossnek CS 594
Computer Science Department
Metropolitan College
Boston University

2. Objectives Review database theory and history
Review relational database concepts
Learn about the evolution of data access technologies
Learn about the ADO.NET namespaces and core classes
Learn how to use ADO.NET classes in an application

3. Agenda
Databases
Relational Databases
ADO.NET Overview
ADO.NET Classes

4. Databases Databases
Virtually all interesting applications require a structured, persistent data store
E-Commerce: placing an order, fulfilling an order
HR: Personnel data
Sales
CRM: Customer data
Games
Database needs vary with the type of application
Transaction Processing/OLTP
Business Intelligence/Data Warehouse/OLAP

5. Databases Database Requirements
Can store, view and modify data
Can move, copy and transform data
Can backup and restore data
Enforces data integrity rules
Is scaleable and available
High number of users
Lots of data
High throughput with low response time
Is secure
Facilitates application development

6. Databases Evolution of Database Technology
File-based
Hierarchical
Network
Relational (RDBMS)
Object-oriented
XML

7. Agenda Databases Theory and History Relational Databases
ADO.NET Overview
ADO.NET Classes

8. Relational Databases Tables
Table (relation, entity)
A collection of data about a specific type of thing
Organized in rows and columns
Column (attribute, field)
Describes part of an entity (e.g. FirstName)
Has a data type (e.g. integer, character, binary)
Can be null
Row (tuple, record)
A single instance of data in a table
Each row is unique
AuthID
FirstName
LastName 1
Joe
Smith 2
Diane
Jones

9. Relational Databases Relating Data
Tables can be related through primary/foreign key relationships (e.g., a book has an author)
Primary key
Guarantees the uniqueness of a row
Can be composed of one or more columns
Ensures entity integrity
Foreign key
Establishes logical relationship between tables
One or more columns of a table that match the primary or alternate key of another table
Referential integrity
Relational databases do NOT get there name because they can relate data. They get their name from set theory: a relation is the set-theoretic term for a table.
Primary/foreign key relationships are THE way data is related in a relational database.

10. Relational Databases Relating Data
Schema diagram depicts tables, columns, primary keys, foreign keys
Books
BookID
AuthID
Title
Type
Authors
AuthID
FirstName
LastName 1 ∞
Schema Diagram

11. Relational Databases Relating Data
Books Table
Primary Key
BookID
AuthID
Title
Type 1 2
My Life as a DBA
Autobiography
Database Handbook
Reference
PK/FK Relationship
Foreign Key
AuthID
FirstName
LastName 1
Joe
Smith 2
Diane
Jones
Authors Table

12. Relational Databases Types of Relationships
One-to-One (1:1)
One row in table X matches one row in table Y
A book has at most one Library of Congress entry
One-to-Many (1:M)
One row in table X matches 0+ rows in table Y
A publisher publishes one or more books
Many-to-Many (M:N)
1+ rows in table X matches 1+ rows in table Y
An author writes one or more books; a book is written by one or more authors 1 1
Books
LoC Entries 1 M
Publishers
Books M N
Authors
Books

13. Relational Databases M:N Relationships
More complex
Can result in very large tables (repeated data)
Difficult to ensure data integrity
The remedy: Create a third table
The third table contains the primary key of the two original tables in a composite key
Data is repeated in the third table, but not in the two original tables
Authors 1 M
BookAuth M 1
Books

14. Relational Databases M:N Relationships1 ∞
Data is duplicated here 1 1 ∞ ∞

15. Relational Databases Normalization/Denormalization
The process of breaking large tables into multiple smaller tables
Goal: minimize redundant data, maximize correctness
Improves performance for updates
Desirable in transaction-based applications
Denormalization
The process of combining smaller tables into fewer larger tables
Goal: improve performance
Introduces redundant data
Improves performance for reads
Desirable in data warehouse applications

16. Relational Databases Joins
A join is a way of combining data in multiple tables, usually by resolving primary key/foreign key relationships
Product table
Vendor table
Product
Cost
Vendor
Vendor
State
Contact
Widget
$10
Acme
Acme MA
Linda A.
Thingy $5
Acme
Blecco WA
Adam P.
Widget $8
Blecco
Foobar
$25
Blecco

17. Relational Databases Joins
Result of a natural join
Product
Cost
Vendor
State
Contact
Widget
$10
Acme MA
Linda A.
Thingy $5
Acme MA
Linda A.
Widget $8
Blecco WA
Adam P.
Foobar
$25
Blecco WA
Adam P.

18. Relational Databases Structured Query Language (SQL)
Standard language for accessing a relational database, standardized by American National Standards Institute (ANSI); SQL-92
Open, but not really
Common functions are mostly the same across products
Most vendors have proprietary extensions
Subsets of SQL
Data Definition Language (DDL)
Data Manipulation Language (DML)
Data Control Language (DCL)

19. Relational Databases DDL Examples
Used to create and modify database objects
CREATE DATABASE Bookstore
CREATE TABLE tBooks (
BookID INT IDENTITY(1,1) PRIMARY KEY,
Title VARCHAR(30) NOT NULL,
PubDate DATE NOT NULL,
[Description] VARCHAR(50),
Category INT NOT NULL )

20. Relational Databases DML Examples
Select data to view
SELECT * FROM tAuthors
SELECT AuthID, FirstName, LastName
FROM tAuthors
SELECT AuthID, FirstName, LastName, Phone
FROM tAuthors
WHERE City = ‘Boston’
SELECT FirstName, LastName, Phone
FROM tAuthors
WHERE AuthID = 249

21. Relational Databases DML Examples
Using SELECT to join tables
SELECT AuthID, FirstName, LastName, Phone,
BookID, Title, PubDate, Description
FROM tAuthors, tBooks
WHERE tAuthors.AuthID = tBooks.AuthID
SELECT AuthID, FirstName, LastName, Phone,
BookID, Title, PubDate, Description
FROM tAuthors INNER JOIN tBooks
ON tAuthors.AuthID = tBooks.AuthID

22. Relational Databases DML Examples
Insert, update and delete data
INSERT INTO tBooks
(Title, PubDate, [Description], Category)
VALUES
(‘Database Design’, GETDATE(),
‘How to design a database’, 3)
UPDATE tAuthors
SET Phone = ‘ ’
WHERE AuthID = 5
DELETE FROM tAuthors
WHERE AuthID = 5

23. Relational Databases DCL Examples
Set security options on database objects
GRANT INSERT, UPDATE, DELETE
ON tAuthors
TO Mary, John
REVOKE CREATE TABLE FROM Joe
DENY ALL
ON tAuthors, tBooks
TO Sally

24. Relational Databases Views
A view is a virtual table
Abstracts the underlying table structures
Abstracts a (possibly complex) query
Provides security abstraction from table
In SQL Server 2000, a view can be
Indexed
Updated and inserted into

25. Relational Databases View Definition Example
CREATE VIEW vwCustomerOrders AS
SELECT o.OrderId, c.CompanyName
FROM Customers c
INNER JOIN Orders o
ON c.CustomerID = O.CustomerID
ORDER BY o.OrderId

26. Relational Databases View Usage Example
SELECT *
FROM vwCustomerOrders
WHERE CompanyName = 'My Favorite Customer'
OrderId
CompanyName
101
My Favorite Customer
137 …

27. Relational Databases Stored Procedures
A group of SQL statements that runs within the database
Not part of SQL standard
Provides greater performance
Can control access to data
Can accept parameters
Can return data
Output parameters
Return values
Result set

28. Relational Databases Stored Procedure Example
CREATE PROCEDURE nchar(5) AS
SELECT ProductName, Total=SUM(Quantity)
FROM Products P, [Order Details] OD, Orders O, Customers C
WHERE C.CustomerID
AND C.CustomerID = O.CustomerID
AND O.OrderID = OD.OrderID
AND OD.ProductID = P.ProductID
GROUP BY ProductName

29. Relational Databases Stored Procedure Examples
exec CustOrderHist 'alfki'
ProductName
Total
Aniseed Syrup 6
Chartreuse verte 21
...

30. Relational Databases Stored Procedure Examples
Use RETURN statement to return status
0 is default in SQL Server
Can only be numeric
Use OUTPUT parameters to return results
RETURN 1
CREATE PROCEDURE INT OUTPUT
...
= ColumnName FROM Table

31. Relational Databases Triggers
Like stored procedures, triggers are code that runs within a database
Not directly called by a user
Executed when a specified data modification takes place (INSERT, UPDATE or DELETE)
Enforces business rules
FOR AFTER: trigger executes after triggering action completes
FOR INSTEAD OF: trigger executes in place of triggering action

32. Relational Databases Transactions
Transaction: a sequence of SQL statements that constitute a logical unit of work
Must adhere to ACID properties
Atomic: All statements execute successfully or all fail
Consistent: Must leave the data in a consistent state when completed
Isolated: Cannot see the modifications made by concurrent transactions
Durable: Must be permanent when complete, even in the event of system failure

33. Relational Databases Concurrency
Isolation levels
Read Uncommitted
Read Committed
Repeatable Read
Serializable
Tradeoffs (concurrency vs. data integrity)
Locking
Ensures transactional integrity/database consistency
Prevents users from seeing “phantom” data
Can result in deadlocks

34. Agenda
Databases
Relational Databases
ADO.NET Overview
ADO.NET Classes

35. ADO.NET Overview Looking Back
ODBC (Open Database Connectivity)
Interoperability to a wide range of database management systems (DBMS)
Widely accepted API
Uses SQL as data access language
DAO (Data Access Objects)
Programming interface for JET/ISAM databases
Uses automation (ActiveX, OLE automation)
RDO (Remote Data Objects)
Tighter coupling to ODBC
Geared more to client/server databases (vs. DAO)

36. ADO.NET Overview Looking Back
OLE DB
Broad access to data, relational and other
Built on COM
Not restricted to SQL for retrieving data
Can use ODBC drivers
Low-level (C++) interface
ADO (ActiveX Data Objects)
Simple component-based, object-oriented interface
Provides a programming model to OLE DB accessible outside of C++

37. ADO.NET Overview Looking Back
Your Application
ADO
OLE DB
ODBC Provider
Simple Provider
Native Provider
ODBC
OLE DB Provider
OLE DB Provider
ODBC Driver
Text File
Mainframe
Database
Database

38. ADO.NET Overview Looking Back
ADO was designed as a connected, tightly coupled model
Appropriate for client/server architectures
Primarily relational (not hierarchical like XML)
Object design is not well factored
Too many ways to do the same thing
Objects try to do too much
Not originally designed for a distributed, n-tier environment

39. ADO.NET Overview What Is ADO.NET?
ADO .NET is a collection of classes, interfaces, structures, and enumerated types that manage data access from relational data stores within the .NET Framework
These collections are organized into namespaces:
System.Data, System.Data.OleDb, System.Data.SqlClient, etc.
ADO .NET is an evolution from ADO.
Does not share the same object model, but shares many of the same paradigms and functionality!

40. ADO.NET Overview ADO.NET Goals
Well-factored design
Highly scaleable through a robust disconnected model
Rich XML support (hierarchical as well as relational)
Data access over HTTP
Maintain familiar ADO programming model
Keep ADO available via .NET COM interoperability

41. ADO.NET Overview Managed Providers
Merges ADO and OLEDB into one layer
Each provider contains a set of classes that implement common interfaces
Initial managed provider implementations:
ADO Managed Provider: provides access to any OLE DB data source
SQL Server Managed Provider: provides optimal performance when using SQL Server
Exchange Managed Provider: retrieve and update data in Microsoft Exchange

42. ADO.NET Overview Managed Providers
Your Application
ADO.NET Managed Provider
SQL Managed Provider
ADO Managed Provider
OLE DB Provider
SQL Server Database
Database

43. ADO.NET Overview Data Access Styles
Connected: Forward-only, read-only
Application issues query then reads back results and processes them
“Firehose” cursor
DataReader object
Disconnected
Application issues query then retrieves and stores results for processing
Minimizes time connected to database
DataSet object
The third main style is connected, scrollable cursor. ADO.NET does not currently support this style, though it may be supported in a future version. This can be implemented by using ADO.

44. ADO.NET Overview Data Binding
Key component of Web Forms framework
Flexible and easy to use
Bind a control’s property to information in any type of data store
Provides control over how data moves back and forth
Simple controls for displaying a single value
Complex controls for displaying a data structure
We will cover this when we discuss ASP.NET and Web Forms.
<asp:Label runat=server Text='<%# CustList(0).FirstName %>'/>

45. Agenda Database Theory and History
Relational Database Concepts and Terminology
ADO.NET Overview
ADO.NET Classes

46. ADO.NET Classes IDbConnection Interface
Creates a unique session with a data source
Implemented by SqlDbConnection and OleDbConnection
Functionality
Open, close connections
Begin transactions
IDbTransaction provide Commit and Rollback methods
Used in conjunction with IDbCommand and IDataAdapter objects
Additional properties, methods and collections depend on the provider
Very similar to ADO counterpart.
Database access protocols tend to be chatty.

47. ADO.NET Classes IDbCommand Interface
Represents a statement to be sent to a data source
Usually, but not necessarily SQL
Implemented by OleDbCommand and SqlCommand
Functionality
Define statement to execute
Execute statement
Pass and retrieve parameters
Create a prepared (compiled) version of command
ExecuteReader returns rows, ExecuteNonQuery doesn’t, ExecuteScalar returns single value
Additional properties, methods and collections depend on the provider
Very similar to ADO counterpart.
Use ExecuteNonQuery whenever possible.

48. ADO.NET Classes IDataReader Interface
Forward-only, read-only (“fire hose”) access to a stream of data
Implemented by SqlDataReader and OleDbDataReader
Created via ExecuteReader method of IDbCommand
Operations on associated IDbConnection object disallowed until reader is closed

49. ADO.NET Classes System.Data.OleDb Namespace
Managed provider for use with OLEDB providers
SQLOLEDB (SQL Server) – use System.Data.SQL
MSDAORA (Oracle)
JOLT (Jet)
OLEDB for ODBC providers
OleDbConnection, OleDbCommand and OleDbDataReader classes
Classes for error handling
Classes for connection pooling

50. ADO.NET Classes DataReader Example
string sConnString = “Provider=SQLOLEDB.1;” +
“User ID=sa;Initial Catalog=Northwind;” +
“Data Source=MYSERVER”;
OleDbConnection conn = new OleDbConnection(sConnString);
conn.Open();
string sQueryString = “SELECT CompanyName FROM Customers”;
OleDbCommand myCommand = new OleDbCommand(sQueryString, conn);
OleDbDataReader myReader = myCommand.ExecuteReader();
while (myReader.Read()) {
Console.WriteLine(myReader.GetString(0)); }
myReader.Close();
conn.Close();

51. ADO.NET Classes DataReader, Insert Demos

52. ADO.NET Classes System.Data Namespace
Contains the core classes of the ADO.NET architecture
Disconnected DataSet is central
Supports all types of applications
Internet based
ASP.NET
XML
Windows forms based

53. ADO.NET Classes System.Data Namespace
Contains classes used by or derived from managed providers
IDbConnection, IDbCommand, IDbDataReader

54. ADO.NET Classes DataSet
A collection of tables
Has no knowledge of the source of the data
Keeps track of all relationships among tables
Rich programming model (has objects for tables, columns, relationships, and so on)
Remembers original and current state of data
Can dynamically modify data and metadata
Native serialization format is XML
Located in System.Data

55. ADO.NET Classes DataSet
DataTable
DataColumn
This is a simplified view of the containment relationships in a DataSet. There are actually many other collections and types of objects involved.
DataRow
DataRelation

56. ADO.NET Classes System.Data.SqlClient Namespace
Managed provider native to SQL Server
Built on TDS (Tabular Data Stream) for high performance in SQL Server
SqlConnection, SqlCommand and SqlDataReader classes
Classes for
Error handling
Connection pooling (implicitly enabled by default )
System.Data.SqlTypes provides classes for native SQL Server data types

57. ADO.NET Classes IDataAdapter Interface
Populates or sends updates to a DataSet
Implemented by OleDbDataAdapter and SqlDataAdapter
Not connection based
Represents an asynchronous approach
A superset of a command object
Contains four default command objects for Select, Insert, Update, and Delete

58. ADO.NET Classes DataSet Example
string sConnString = “Persist Security Info=False;” +
“User ID=sa;Initial Catalog=Northwind;” +
“Data Source=MYSERVER”;
SqlConnection conn = new SqlConnection(sConnString);
conn.Open();
string sQueryString = “SELECT CompanyName FROM Customers”;
SqlDataAdapter myDSAdapter = new SqlDataAdapter();
DataSet myDataSet = new DataSet();
myDSAdapter.SelectCommand = new SqlCommand(sQueryString, conn);
myDSAdapter.Fill(myDataSet);
conn.Close();

59. ADO.NET Classes DataSet Demo

60. ADO.NET Classes Stored Procedure Demo

61. ADO.NET Classes DataTable
In-memory object representing one table
Columns
Rows
Schema defined by Columns collection
Data integrity provided through Constraint objects
Public events
Modifying/deleting rows
Modifying columns

62. ADO.NET Classes DataColumn
Fundamental building block of a DataTable schema (contained in Columns collection)
Defines what type of data may be entered (via DataType property)
Other important properties include AllowNull, Unique, and ReadOnly
Can contain Constraints (a collection on DataTable)
Can contain Relations (collection on DataSet)

63. ADO.NET Classes DataRow
Represents data in a DataTable (contained in Rows collection)
Conforms to schema defined by DataColumns
Properties for determining row state (e.g., new, changed, deleted, etc.)
All additions/modifications “committed” with AcceptChanges method of DataTable

64. ADO.NET Classes DataRelation
Relates two DataTables via DataColumns
DataType value of both DataColumns must be identical
Updates can be cascaded to child DataTables
Modifications that invalidate the relation are disallowed

65. ADO.NET Classes Creating a DataSet in Code
Create DataSet
Define tables
DataSet dataset = new DataSet();
dataset.DataSetName = “BookAuthors”;
DataTable authors = new DataTable(“Author”);
DataTable books = new DataTable(“Book”);

66. ADO.NET Classes Creating a DataSet in Code
Define columns
Define keys
DataColumn id = authors.Columns.Add("ID", typeof(Int32));
id.AutoIncrement = true;
authors.PrimaryKey = new DataColumn[] {id};
DataColumn name
= new authors.Columns.Add("Name",typeof(String));
DataColumn isbn = books.Columns.Add("ISBN", typeof(String));
books.PrimaryKey = new DataColumn[] {isbn};
DataColumn title = books.Columns.Add("Title", typeof(String));
DataColumn authid = books.Columns.Add(“AuthID”,typeof(Int32));
DataColumn[] foreignkey = new DataColumn[] {authid};

67. ADO.NET Classes Creating a DataSet in Code
Add the tables to the DataSet
dataset.Tables.Add (authors);
dataset.Tables.Add (books);

68. ADO.NET Classes Creating a DataSet in Code
Add data and save the DataSet
DataRow shkspr = authors.NewRow();
shkspr["Name"] = "William Shakespeare";
authors.Rows.Add(shkspr);
DataRelation bookauth = new DataRelation("BookAuthors",
authors.PrimaryKey, foreignkey);
dataset.Relations.Add (bookauth);
DataRow row = books.NewRow();
row["AuthID"] = shkspr["ID"];
row["ISBN"] = "1000-XYZ";
row["Title"] = "MacBeth";
books.Rows.Add(row);
dataset.AcceptChanges();

69. ADO.NET Classes DataSet Creation Demo

70. ADO.NET Classes Typed DataSets
Derived from base DataSet class
Uses XML schema to generate new class
Tables, columns, etc. compiled into new class
ds.Customers.FirstName
Untyped DataSet
No built-in schema
Tables, columns, etc. exposed only as collections
ds.Tables[“Customers”].Rows[0][“FirstName”]

71. ADO.NET Classes Errors and Exceptions
Error class
Contains information on an error or warning returned by data source
Created and managed by Errors class
Errors class
Contains all errors generated by an adapter
Created by Exception class
Exception class
Created whenever an unhandled error occurs
Always contains at least one Error instance

72. ADO.NET Classes Errors and Exceptions Example
try {
DataTable myTable = new DataTable();
myTable.Columns.Add(“myCol”);
//whoops! }
catch (DataException myException) {
Console.WriteLine ("Message: " + myException.Message + "\n" +
"Source: " + myException.Source + "\n" +
“Stack Trace: " + myException.StackTrace + "\n");

73. ADO.NET Classes DataException Demo

74. Conclusion Database Theory and History
Relational Database Concepts and Terminology
ADO.NET Overview
ADO.NET Classes

75. Resources Introducing ADO+ ADO.NET
ADO.NET
ADO+ Guides the Evolution of the Data Species
ADO.NET for the ADO Programmer
ADO Rocks and Rolls in .NET Applications
Meditating on OLE DB and .NET

76. Resources Reading Data Reader Secrets Database-like Data Containers
Database-like Data Containers
ADO
Universal Data Access
SQL Server

77. Appendix ADO vs. ADO.NET
ADO is a slower automation layer over OLE DB for use in Visual Basic, etc.
ADO.NET provides direct, fast access to data from any language
ADO.NET essentially has merged OLE DB and ADO into a single layer

78. Appendix ADO vs. ADO.NET Feature ADO ADO.NET
Memory-resident Data Representation
Uses RecordSet, which can contain one table
Uses DataSet, which can contain one or more tables represented by DataTables
Relationship Between Multiple Tables
Require the JOIN query
Supports the DataRelation object
Data Visitation
Scans RecordSet rows sequentially
Uses a navigation paradigm for non-sequential access
Disconnected Access
Provided by RecordSet but typically supports connected access
Communicates with standardized calls to the DataAdapter
KEY MESSAGE:
SLIDE BUILDS: None
SLIDE SCRIPT:
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ADDITIONAL INFORMATION FOR PRESENTER:

79. Appendix ADO vs. ADO.NET Feature ADO ADO.NET Programmability
Uses Connection object to transmit commands
Uses strongly typed programming characteristics of XML
Sharing Disconnected Data Between Tiers or Components
Uses COM marshalling to transmit disconnected Recordset
Transmits a DataSet with an XML file
Transmitting Data Through Firewalls
Problematic because firewalls are typically configured to prevent system-level requests
Supported, DataSet object use XML, which can pass through firewalls
Scalability
Database locks and active database connections for long durations
Disconnected access to database data without retaining database locks
KEY MESSAGE:
SLIDE BUILDS: None
SLIDE SCRIPT:
SLIDE TRANSISTION:
ADDITIONAL INFORMATION FOR PRESENTER: