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February 2nd, 2006 ADO .NET 2
Contents
Introduction
What is ADO.NET?
Data Access
Motivation - Why Moving to ADO.NET?
ADO.NET Objects Content components Managed-provider components
ADO.NET & Transactions
ADO.NET and XML
.NET Framework Data Providers
ADO.NET 2.0 Added Features
Summary - Pros & Cons
February 2nd, 2006 ADO .NET 3
What is ADO.NET?
ADO.NET (ActiveX Data Objects) is the primary relational data access model for Microsoft .NET-based applications.
The data access objects role is to serve as an interface between the client application and the data provider – the DBMS. This modularity results in two big advantages:
Allowing the writing of applications that use standard types and features, resulting in DBMS independent code.
Unified API for the database driver implementers.
February 2nd, 2006 ADO .NET 4
Things Weren’t Always So Simple…
Let’s have a Brief Look at the evolution that lead to ADO.NET At first, programmatic access to databases was performed by
native libraries, such as DBLib for SQL Server, and the Oracle Call Interface (OCI) for Oracle.
This allowed for fast database access because no extra layer was involved.
However, it also meant that modularity was absent. i.e. loosing the two advantages discussed on the previous slide.
February 2nd, 2006 ADO .NET 5
Data Access Evolution (1)
ODBC:
As a solution, Microsoft and other companies developed the Open Database Connectivity, or ODBC.
This provided a common data access layer, which could be used to access almost any relational database management system.
In practice, there were some differences in the SQL dialect supported hence, violating the main principle of modularity.
Nonetheless, perhaps the most important feature of ODBC is the fact that it was an open standard, widely adopted even by the Open Source community.
February 2nd, 2006 ADO .NET 6
Data Access Evolution (2)
DAO: As the importance of Visual Basic grew, there was a need for a
data access technology that could be used more naturally from VB.
DAO (Direct Access Objects) provided a simple object model for talking to Microsoft's Access desktop database. As DAO was optimized for Access, it was very fast.
RDO: Due to its optimization for Access, DAO was very slow when
used with ODBC data sources. To get round this, Microsoft introduced Remote Data Objects (RDO).
RDO was designed specifically for access to ODBC data sources. RDO is essentially a thin wrapper over the ODBC API.
February 2nd, 2006 ADO .NET 7
Data Access Evolution (3)
OLE DB: As part of the OLE (Object linking and Embedding) distributed
object system, the OLE DB is used for accessing different types of data stores in a uniform manner.
ADO: ActiveX Data Objects is the technology that gave its name to
ADO.NET (although in reality the differences are far greater than the similarities).
ADO is merely an OLE DB consumer – a thin layer allowing users of high -level languages to access OLE DB through a simple object model.
In a way, ADO is to OLE DB more or less what RDO was to ODBC
February 2nd, 2006 ADO .NET 8
Why Moving to ADO.NET?
Why not simply continue to use ADO in the .NET framework? It's perfectly possible to carry on using ADO in .NET
applications through COM interoperability. However, there are some very good reasons why ADO wasn't
really suited to the new programming environment:
Using Managed Classes Cleaner Architecture Cross-Language Support XML Support Optimized Object Model
February 2nd, 2006 ADO .NET 9
Why Moving – Managed classes & Cleaner Architecture
Using Managed Classes The alternative - using .NET then COM interoperability - adds
overhead to the application. Takes advantage of the benefits of the CLR such as JIT
compilation and the managed execution environment.
Cleaner Architecture As we noted above, ADO is no more than a thin layer over
OLE DB. ADO.NET can be much faster than ADO, as the providers
communicate directly with the data source.
February 2nd, 2006 ADO .NET 10
Why Moving – Cross-Language Support & XML Support
Cross Language Support ADO was aimed primarily at VB programmers. This lead to
using optional method parameters, which are not supported by C-based languages such as C#.
This means that if you use ADO from C#, you will need to specify all parameters in method calls. This makes ADO programming under .NET considerably more time-consuming
XML Support XML is absolutely integral to ADO.NET, and not just an add-
on. As we shall see later on in the demo, XML is the format used
to serialize and transport DataSets.
February 2nd, 2006 ADO .NET 11
Why Moving – Optimized Object Model
Optimized Object Model The .NET Framework is aimed squarely at developing
distributed applications, and particularly Internet-enabled applications.
In this context, for example, we don't want to hold a connection open for a long time, as this could create a bottleneck and destroy scalability.
ADO didn't encourage disconnected recordsets, whereas ADO.NET has different classes for connected and disconnected access, and doesn't permit updateable connected recordsets.
February 2nd, 2006 ADO .NET 12
ADO .NET - Objects
.Net Data Provider.Net Data Provider DataSetDataSet
ConnectionConnection
TransactionTransaction
CommandCommand
ParametersParameters
DataReaderDataReader
Data AdapterData Adapter
SelectSelect
InsertInsert
DeleteDelete
UpdateUpdate
DataRelationsDataRelations
Data TableData Table
DataColumnDataColumn
DataRowDataRow
ConstraintsConstraints
DBDB <XML><XML>
February 2nd, 2006 ADO .NET 13
ADO .NET – Objects(2)
In ADO .NET there are two class groups.
Content components
Managed-provider components
February 2nd, 2006 ADO .NET 14
ADO .NET – Objects(3)
Content components The content components hold actual data and include
DataSet DataTable DataView
DataColumn DataRow
DataRelation
Managed-provider components These components actually talk to the database to assist in data
retrievals and updates. Such objects include the Connection, Command, Data Reader and Data Adapter.
The managed-provider components are split into several groups designed for each provider as we will see later.
February 2nd, 2006 ADO .NET 15
Connection
Connection
Provides a connection to the database . There are typical Open() and Close(), plus BeginTransaction() returning an object to control a database transaction.
To open a connection to a data source you need to provide a connection string.
Example: "Network Library=DBMSSOCN; Data Source=132.245.124.37,1433;Initial
Catalog=myDatabaseName;User ID=myUsername;Password=myPassword"
February 2nd, 2006 ADO .NET 16
Connection(2)
Managing Database Connections
DB connection represent a critical expensive and limited resource.
Connection Pooling
Open connections late and close them early
February 2nd, 2006 ADO .NET 17
Connection Pooling
Connection Pooling Database connection pooling enables an application to reuse an
existing connection from a pool, instead of repeatedly establishing a new connection with the database.
ADO .NET data providers provide transparent connection pooling, the exact mechanics of which vary for each provider.
For example, using SQL Server .Net data provider you can configure connection pooling by adding a name-value pairs to the connection string: “[…];Max Pool Size=75; Min Pool Size=5”
Connections are pooled through an exact match algorithm on the connection string!!! The pooling mechanism is even sensitive to spaces between name-value pairs.
February 2nd, 2006 ADO .NET 18
Command
Command This is the pipeline to the backend data.
The command object provides direct execution of the SQL command to the database.
You can use the command to either ExecuteNonQuery(), which will action an SQL statement (such as a DELETE command) upon the data.
ExecuteReader() links straight in to the Data Reader object.
February 2nd, 2006 ADO .NET 19
Commands and Parameters
Commands and Parameters
When a SQL statement is executed, the database has to generate an execution plan for it.
Use Prepare() method to generate and store an execution plan in advance. The plan will be saved in the database cache so subsequent statements will be executed much faster.
This method should be used only if the SQL statement will be executed multiple times.
Use Parameter object, instead of hardcoding parameter values in a SQL statement.
February 2nd, 2006 ADO .NET 20
Parameters - Example
string sConnString = "Server=(local);Database=Northwind;Integrated Security=True;";
string sSQL = "UPDATE Customers SET City=@sCity WHERE CustomerID=@sCustomerID";
SqlConnection oCn = new SqlConnection(sConnString))
SqlCommand oCmd = new SqlCommand(sSQL, oCn))
oCmd.CommandType = CommandType.Text;
oCmd.Parameters.Add("@sCustomerID", SqlDbType.NChar, 5);
oCmd.Parameters.Add("@sCity", SqlDbType.NVarChar, 15);
oCn.Open();
oCmd.Prepare(); // Prepare the execution plan
oCmd.Parameters["@sCustomerID"].Value = "ALFKI";
oCmd.Parameters["@sCity"].Value = “Jerusalem";
oCmd.ExecuteNonQuery();
oCmd.Parameters["@sCustomerID"].Value = "CHOPS";
oCmd.Parameters["@sCity"].Value = “Tel-Aviv";
oCmd.ExecuteNonQuery();
oCn.Close();
February 2nd, 2006 ADO .NET 21
Data Reader
Data Reader
This object essentially takes a stream of data from the Command object and allows you to read it.
It's like a forward-only Recordset from the ADO and is very efficient because it stores only one record in the memory at a time.
However this uses a server-side cursor, so you should avoid it too much as it naturally requires an open connection.
February 2nd, 2006 ADO .NET 22
Data Adapter
Data Adapter
It essentially serves as a middle man, going through your connection to retrieve data, then passing that into a DataSet.
You can then pass the DataSet back to the Data Adapter, which will go and update the database.
The SQL statements for each command are specified in the
InsertCommand, UpdateCommand, SelectCommand and DeleteCommand properties.
February 2nd, 2006 ADO .NET 23
DataSet
DataSetDataSet
DataTableDataTable
RelationsRelations
XML SchemaXML Schema
DataTableDataTable
DataColumnDataColumn
DataRowDataRow
ConstraintsConstraints
February 2nd, 2006 ADO .NET 24
DataSet(2)
DataSet
The “king” of the ADO .NET
This object is actually a memory resident representation of data that provides a consistent relational programming model regardless of the data source.
The data stored in the DataSet object is disconnected from the database!
February 2nd, 2006 ADO .NET 25
DataSet(3)
The DataSet object model is made up of three collections, Tables, Relations and ExtendedProperties. These collections make up the relational data structure of the DataSet
Tables Collection
Relations Collection
ExtendedProperties Collection
February 2nd, 2006 ADO .NET 26
DataSet(4) Tables Collection
DataSet.Tables Each DataTable represents a table of data from the data source. DataTable is made up of a Columns collection and a Rows collection.
Relations Collection DataSet.Relations The DataRelation objects define a parent-child relationship between
two tables based on foreign key values.
ExtendedProperties Collection DataSet.ExtendedProperties The ExtendedProperties is a user-defined properties collection. Can be used to store custom data related to the DataSet, such as the
time when the DataSet was constructed.
February 2nd, 2006 ADO .NET 27
DataSet(5)
DataSet
DataTable
DataView
PrimaryKey
DataRow
DataColumn
DataRelationCollectionDataRelationCollection
ExtendedPropetiesExtendedPropeties
DataTableCollectionDataTableCollection
ChildRelationsChildRelations
ParentRelationsParentRelations
ConstraintsConstraints
ExtendedPropertiesExtendedProperties
DataColumnCollectionDataColumnCollection
DataRowCollectionDataRowCollection
ExtendedPropertiesExtendedProperties
February 2nd, 2006 ADO .NET 28
DataSet(6)
Connecting a DataSet to a data source
In order to connect a DataSet to a data source, we need to use the DataAdapter as an intermediary between the DataSet and the .NET data provider.
Let’s see some code…
February 2nd, 2006 ADO .NET 29
DataSet – Example
Filling the DataSet:
// Connection StringString conStr = @"Provider=Microsoft.Jet.OLEDB.4.0;DataSource=C:\
NWind.mdb";//SQL CommandString sqlStr = "SELECT EmployeeID, FirstName, LastName FROM
Employees";// Create a new DataAdapter objectOleDbDataAdapter da = new OleDbDataAdapter(sqlStr, conStr);// Create a new DataSetDataSet ds = new DataSet();// Fill the DataSetda.Fill(ds, "Employees");
February 2nd, 2006 ADO .NET 30
Transactions
Why do we need transactions? Consider a Web-based retail application that processes purchase
orders. Each order requires three distinct operations that involve three database updates:
The inventory level must be reduced by the quantity ordered. The customer’s credit level must debited by the purchase amount. A new order must be added to the orders database.
It is essential that these three distinct operations be performed as a unit and in atomic fashion.
February 2nd, 2006 ADO .NET 31
Transactions(3)
Performing Manual Transactions with ADO .NET ADO .NET supports a transaction object that you can use to begin a
new transaction and then explicitly control whether it should be committed or rolled back.
The transaction object is associated with a single database connection and obtained by the BeginTransaction() method of the connection object.
You must explicitly associate each command objects with the transaction by setting the Transaction property.
Note that since a transaction object associated with a single connection you can perform transactions only with a single database.
February 2nd, 2006 ADO .NET 32
Transactions – Example
Transaction Example SqlConnection db = new SqlConnection(conStr); SqlTransaction transaction;
db.Open(); transaction = db.BeginTransaction(); try { new SqlCommand("INSERT INTO TransactionDemo(Text) VALUES ('Row1')", db,
transaction).ExecuteNonQuery(); new SqlCommand("INSERT INTO TransactionDemo(Text) VALUES ('Row2');",db,
transaction).ExecuteNonQuery(); new SqlCommand("INSERT INTO CrashMeNow VALUES ('Die', 'Die', 'Die');", db,
transaction).ExecuteNonQuery(); transaction.Commit(); } catch (SqlException sqlError) { transaction.Rollback(); } db.Close();
February 2nd, 2006 ADO .NET 33
ADO .NET and XML
XML and Traditional Data Access
We have talked about data access as it relates to traditional data access and relational data.
A wide variety of data can be represented in a non relational way.
ADO .NET makes it extremely easy to create and read XML documents.
The data in ADO.NET is transported in XML format.
You can parse XML in .NET programmatically using the System.Xml.XmlDataDocument object.
February 2nd, 2006 ADO .NET 34
ADO .NET and XML (2)
Saving DataSet as XML
Fill the DataSet with data. Use DataSet.WriteXml(fileName) to write an XML file.
Loading XML files
Loading the XML file is not more complex than writing it. Use DataSet.ReadXml(fileName) to load the data. Wrap ReadXml call with try and catch because we can’t guarantee
that the file contains valid XML.
February 2nd, 2006 ADO .NET 35
ADO .NET and XML (3)
Schemas
Schemas provide a mechanism for defining rules that XML documents must adhere to, and which help everyone understand what the data held in an XML document actually is.
Generating a Schema
Fill the dataset DataSet.WriteXmlSchema(SchemaFileName);
February 2nd, 2006 ADO .NET 37
ADO .NET and XML (5)
Typed DataSets
Typed DataSets can provide a more intuitive mechanism for the manipulation of data.
A typed DataSet is early bound to an XML Schema Definition (XSD) file.
Schemas provide very rigorous definitions for the types of particular objects. In conjunction with the typed DataSet, they can allow access to the tables and columns of a DataSet using meaningful names.
This not only improves the readability of the code Enables Visual Studio .NET's IntelliSense feature to make context-
sensitive suggestions as you type in code.
February 2nd, 2006 ADO .NET 38
Data Providers Diagram
COM InterOp
OLE DB .Net Data ProviderOLE DB .Net Data Provider
OleDbConnectionOleDbConnection
OleDbCommandOleDbCommand OleDbDataReaderOleDbDataReader
OleDbDataAdapterOleDbDataAdapter
SQL Server 6.5 and earlierSQL Server 6.5 and earlier
Data TableData Table
DataSet
SQL Server/Oracle SQL Server/Oracle .Net Data Provider.Net Data Provider
ConnectionConnection
CommandCommand DataReaderDataReader
DataAdapterDataAdapter
SQL Server 7.0 and later / OracleSQL Server 7.0 and later / Oracle
OLE DB
..NET Managed AppNET Managed App
UnmanagedUnmanaged AppApp
ADO
SQLOLEDB
Misc DBMisc DB
February 2nd, 2006 ADO .NET 39
Data Providers in the .NET (1) Framework
SqlClient Provider Should be used to access SQL Server 7.0 or later, and MSDE
databases. Can't be used with SQL Server 6.5 or earlier.
OleDb Provider Good for almost anything other than SQL Server 7.0 or later,
or Oracle. Using the ODBC data access through the OleDb is
discouraged – think of the architecture involved: ADO.NET – COM interop – (optional) OLE DB services –
OLE DB provider – ODBC driver – data source!
February 2nd, 2006 ADO .NET 40
Data Providers in the .NET (2) Framework
The Odbc Provider Should be used whenever you need to access a data source
with no direct or OLE DB provider (PostgreSQL, Paradox, dBase…),
OracleClient Provider Supports Oracle data types, as well as ref cursors Avoids the cost of COM interop, and also employs Oracle-
specific optimizations
February 2nd, 2006 ADO .NET 41
Generic Interfaces
ADO.NET was designed from the beginning to allow the provider writer the space to support database-specific features.
Programmers who wish to build applications that interact with databases of more than one brand may resort to the generic interfaces:
IDbConnection IDbCommand IDataReader IDbTransaction IDbDataParameter IDataParameterCollection IDbDataAdapter
There are problems involved with a common interface instead of a common base class. This issue will be covered in more depth in the slides about ado.net
2.0
February 2nd, 2006 ADO .NET 42
ADO.NET 2.0 Added Features
ADO.NET 2.0 comes with a plethora of new features. We shall cover the main features in short:
Based-Class-Based Provider Model Provider Factories Asynchronous Commands SqlDependency MARS (Multiple Active Resultsets)
February 2nd, 2006 ADO .NET 43
ADO.NET 2.0 Added Features (1)
Based-Class-Based Provider Model In ADO.NET 1.X provider writers implemented a series of
provider-specific classes. Generic coding was based on the generic interface each of the classes implemented.
The new provider model in ADO.NET 2.0 is based on a series of base classes.
Each of the base classes implements the still-required generic interface for backward compatibility.
Provider Factories The base ProviderFactory class (DbProviderFactory) and the
ProviderFactories class (System.Data.Common.ProviderFactories) simplify things a bit…
February 2nd, 2006 ADO .NET 44
ADO.NET 2.0 Added Features (2)
Conditional code that used to be written like this:
enum provider {sqlserver, oracle, oledb, odbc};// determine provider from configuration provider prov = GetProviderFromConfigFile();IDbConnection conn = null;
switch (prov) { case provider.sqlserver:
conn = new SqlConnection(); break; case provider.oracle:
conn = new OracleConnection(); break; case provider.oledb:
conn = new OleDbConnection(); break; case provider.odbc:
conn = new OdbcConnection(); break; // add new providers as the application supports them …
}
February 2nd, 2006 ADO .NET 45
ADO.NET 2.0 Added Features (3)
...Can now be written like this:
// get ProviderInvariantString from configuration string provstring = GetProviderInvariantString(); DbProviderFactory fact = DbProviderFactories.GetFactory(provstring); IDbConnection = fact.CreateConnection();
February 2nd, 2006 ADO .NET 46
ADO.NET 2.0 Added Features (4)
Asynchronous Commands database command execution can take a long time. ADO.NET 2.0 SqlClient now provides built-in SqlCommand
methods that provide asynchronous execution.
SqlDependency Caching is good. But we should make sure it’s consistent with
the database. Until now, this task was accomplished through triggers
that updated a file upon update of the database, or by refreshing the cache every so often.
February 2nd, 2006 ADO .NET 47
ADO.NET 2.0 Added Features (5)
SqlDependency contacts you when the underlying rows change.
When notified, the entire set of rows is fetched again. This functionality is good for a single cache or a limited set of
users. However, when using it with large numbers of users listening at
the same time - the SELECT statements used for refresh could be a significant hit on the database.
February 2nd, 2006 ADO .NET 48
ADO.NET 2.0 Added Features (6)
MARS (Multiple Active Resultsets)
SQL Server doesn't automatically produce a cursor. Instead, it uses an optimized method to pull the data in packet-size chunks.
In the versions prior to SQL Server 2005, there could only be one cursorless resultset active on a connection at a time.
ADO.NET 1.X throw an error if you attempt to open a second cursorless resultset.
ADO "classic" actually opened a new database connection behind the scenes.
This convenience feature was inadvertently abused by some programmers and resulted in more database connections than they bargained for.
February 2nd, 2006 ADO .NET 49
ADO.NET 2.0 Added Features (7)
MARS (contd)
In SQL Server 2005, the database has been enhanced to permit MARS.
Each SqlCommand can accommodate a SqlDataReader, and multiple SqlDataReaders can be used in tandem.
It’s not just about reducing errors. It can be extremely useful in conjunction with asynchronous operations described above.
Example: Filling 20 drop-down list boxes on a form at the same time, using a single connection.
February 2nd, 2006 ADO .NET 50
Summary: Pros & Cons
Pros Performance Managed Classes XML Support (and Reliance) Disconnected Operation Model Rich Object Model
Cons Managed-Only Access Only four Managed Data Providers (so far) Learning Curve
February 2nd, 2006 ADO .NET 52
Installation
Installing .Net Framework 1.1 is free http://msdn.microsoft.com/netframework/downloads/framework1_1/
Getting Visual Studio 2003 is not free http://msdn.microsoft.com/vstudio/Previous/2003/
There is VS Academic “only” for $99
Installing SQL Server 2000 http://www.microsoft.com/technet/prodtechnol/sql/2000/downloads/
NEXT->NEXT->… -> FINISH