ADO.NET

1. ADO.NET Andrei Otcheretianski Tomer Rothschild

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 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. 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. 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. 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. 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 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 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. 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 allparameters 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. 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. ADO .NET

12. DataColumn DataRow ADO .NET - Objects DataSet .Net Data Provider Data Adapter Connection Select Transaction Data Table Insert Command Constraints Parameters Update DataReader Delete DataRelations DB <XML> ADO .NET

13. ADO .NET – Objects(2) • In ADO .NET there are two class groups. • Content components • Managed-provider components 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. 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" 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 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. 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. 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. 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(); 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. 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. ADO .NET

23. DataColumn DataRow DataTable DataSet DataTable DataSet Relations Constraints XML Schema 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! 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 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. ADO .NET

27. DataSet(5) DataSet DataRelationCollection ExtendedPropeties DataTableCollection DataTable DataRowCollection DataView DataRow ChildRelations ParentRelations Constraints DataColumnCollection DataColumn ExtendedProperties ExtendedProperties PrimaryKey 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… ADO .NET

29. DataSet – Example • Filling the DataSet: // Connection String String conStr = @"Provider=Microsoft.Jet.OLEDB.4.0;DataSource=C:\NWind.mdb"; //SQL Command String sqlStr = "SELECT EmployeeID, FirstName, LastName FROM Employees"; // Create a new DataAdapter object OleDbDataAdapter da = new OleDbDataAdapter(sqlStr, conStr); // Create a new DataSet DataSet ds = new DataSet(); // Fill the DataSet da.Fill(ds, "Employees"); 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. 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. 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(); 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. 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. 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); ADO .NET

36. ADO .NET and XML (4) 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. ADO .NET

38. OLE DB .Net Data Provider OleDbConnection OleDbDataAdapter DataSet OleDbDataReader OleDbCommand SQL Server/Oracle .Net Data Provider Data Table DataAdapter Connection DataReader Command Misc DB Data Providers Diagram Unmanaged App SQL Server 7.0 and later / Oracle .NET Managed App ADO COM InterOp OLE DB SQLOLEDB SQL Server 6.5 and earlier 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! 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 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 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) 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… 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 … } 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(); 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. 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. 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. 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. 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 ADO .NET