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ADO.NET 2.0

ADO.NET 2.0. Architecture DataReader DataSet Connection factory Config file. Data access. Swap?. Data Providers. OLE DB: A COM object, that maps the OLE DB api to the DBMS' api Is Microsoft propritary. ODBC: Works similar to a printer driver undependent of DBMS and OS

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ADO.NET 2.0

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  1. ADO.NET 2.0 • Architecture • DataReader • DataSet • Connection factory • Config file

  2. Data access Swap?

  3. Data Providers • OLE DB:A COM object, that maps the OLE DB api to the DBMS' apiIs Microsoft propritary. • ODBC: Works similar to a printer driver undependent of DBMS and OS • .NET Data provider:A set of classes that implements a set of interfaces and abstract classes • Some are provided by Microsoft and are installed with the .Net framework. • Others are written by the DBMS provider

  4. Microsoft Data Providers • Data Provider Namespace Assembly • OLE DB System.Data.OleDb System.Data.dll • Microsoft SQL Server System.Data.SqlClient System.Data.dll • Microsoft SQL Server Mobile System.Data.SqlServerCe System.Data.SqlServerCe.dll • ODBC System.Data.Odbc System.Data.dll • Oracle System.Data.OracleClient System.Data.OracleClient.dll MS Access

  5. Other providers • Data Provider Website • Firebird Interbase http://www.mono-project.com/Firebird_Interbase • IBM DB2 Universal Database http://www-306.ibm.com/software/data/db2 • MySQL http://dev.mysql.com/downloads/connector/net/1.0.html • PostgreSQL http://www.mono-project.com/PostgreSQL • Sybase http://www.mono-project.com/Sybase • Oracle (proprietary) http://www.oracle.com/technology/tech/windows/odpnet/index.html

  6. Classes and Interfaces • Object Base Class Implemented Interfaces • Connection DbConnection IDbConnection - Connection • Command DbCommand IDbCommand - SQL command • DataReader DbDataReader IDataReader - Forward reader • DataAdapter DbDataAdapter IDataAdapter - Used with Dataset • Parameter DbParameter IDataParameter - Parameters for Command • Transaction DbTransaction IDbTransaction - Transaction

  7. Two ways of DB access Connected: Open connection. Read/Write access (select, insert, update and delete) using a Command object. When reading (select) a DataReader object is returned. A DataReader is an iterator (cursor) into the result table. Close Connection. Disconnected: Fill a DataSet object (a copy of a part of the database) using a DataAdapter. DataAdapter wraps SQL-statement(s). A DataSet object contains DataTable objects. DataTable objects contain collections of rows and columns.

  8. Connection vs. Connectionless Connection: Open Connection Execute DB operations Close Connection Working on actual (live) data Other applications can not access data.

  9. Connection vs. Connectionless • Connectionless: • Create a copy of a part of the database • Execute DB operations on the copy • Other applications may change date • The copy may be come inconsistent. • Data are changed in the local copy: • at update it is checked if the data in the database have been modified by others • in that case the update is rejected (ConcurrencyException).

  10. Overview of using databases • 4 steps: • Open connection to database • Execute SQL for updating DB or fetching records • Handle data • Close connection

  11. connection Step 1: Open Connection • Connection are opened according to connection string info • here is a connection to a MS Access database opened • The database is located here: @"c:\AnyPlace\MyDb.mdb" • @ means that escape characters are discarded <%@ import namespace="System.Data"%><%@ import namespace="System.Data.OleDb"%> string sConnection; sConnection = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source="+@"c:\AnyPlace\MyDb.mdb"); OleDbConnection dbConn; dbConn = new OleDbConnection(sConnection); dbConn.Open();

  12. Open Connection Connections are opened using a connection string May be found using Visual Studio: Data Source or Server? // Create and open a connection. SqlConnection cn = new SqlConnection(); cn.ConnectionString = "Data Source=PCM06073\\SQLEXPRESS;” +”Initial Catalog=vw;Integrated Security=True;"; cn.Open(); ShowConnectionStatus(cn); // or should it be? cn.ConnectionString = “Server=PCM06073\\SQLEXPRESS;” +”Initial Catalog=vw;Integrated Security=True;"; cn.Open(); Server is preferable.

  13. Connection Strings Connection strings are product specific (DB specific) anf often very well-documented. Help may be found at: www.connectionstrings.com www.able-consulting.com/ADO_conn.htm In many cases VS can help.

  14. Step 2: Get / fetch data • Data are fetched by creating a Command object and use it to execute a SQL statement. • Data can be stored in either a DataReader object or a DataSet object.

  15. Differences between DataReader and DataSet/DataAdapter • DataReader can only be used for reading data. • It can only be traversed once (forward). • DBCommand can update the database by ExecuteNonQuery. This update is executed immediately. • DataAdapter is the connection between DataSet and database. • Data are fetched to the DataSet, might be modified and sent back to the database. • Updates are executed on a local copy. Concurrency problems must be handled. • Possible to traverse forward and backward. • A DataSet can contain multiple tables.

  16. dataset record record record Step 2: Get records Method 1: DataSet • Get records by SQL Select query and DataAdapter • Data can be read and changed string sql; sql = " Select lastname, firstname" + " From employee" + " Order By lastname Asc, firstname Asc;"; OleDbCommand dbCmd; dbCmd = new OleDbCommand(dbConn, sql); adapter.SelectCommand = dbCmd; dataset =new DataSet("MyTable"); adapter.Fill(dataset);

  17. data reader record record record Step 2: Get records Method 2: DataReader • Get records via SQL Select query • read-only access to the database string sql; sql = " Select lastname, firstname" + " From employee" + " Order By lastname Asc, firstname Asc;"; OleDbCommand dbCmd; dbCmd = new OleDbCommand(sql, dbConn); OleDbDataReader dbReader; dbReader = dbCmd.ExecuteReader();

  18. What is achieved? • We have created a connection to a database. • The connection is placed in the connection object. • We have done a search by using a SQL-statement. • The search was executed by using a command object. • The result of the search was stored in a DataSet or as here a DataReader object. • Now it is possible to get the data from this object for viewing, passing on to client or handle in other ways. Example: ..\vwReader

  19. Factory • Problem: Unlike ODBC, knowledge of the implementationmightbespread to manyplaces in the application.That'sbecause of the set of dedicatedclasses • The solution is to use a factory (from factory pattern) • In ADO.NET 2.0, it is implementet in the framework. • Usefactory to create a Connection and a Command object Example: \ReaderWithConfig

  20. Use factory to create Connection and Command objects • Here is no references in the source code to concrete classes • provider and connectionString may be placed in the config file string provider = "System.Data.OleDb"; string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=firma.mdb"; DbProviderFactory factory= DbProviderFactories.GetFactory(provider); DbConnection conn=factory.CreateConnection(); conn.ConnectionString=connectionString; conn.Open(); Console.WriteLine(conn.State); DbCommand command = factory.CreateCommand(); command.CommandText = "SELECT * FROM employee"; command.Connection = conn; DbDataReader dataReader = command.ExecuteReader(); while (dataReader.Read()){ Console.WriteLine(dataReader[1]); }

  21. Connection strings • Connection strings depends on the provider and are not well documented • Where to get help? • www.connectionstrings.com • www.carlprothman.net/Default.aspx?tabid=81 • Providers documentation • Visual Studio can generate some of them

  22. .Config fil • Configuration files are used several places in .Net • i.e in ASP.NET for setting site properties and security • In Remoting for setting remote object properties • In ADO.NET to set provider and connection string • You might also use own application dependent properties • In a .Net application the config file should be called<full assemblyname.config>, i.e test.exe.config or test.dll.config • If you call it app.config in Visual Studio, it automatically copied and renamed when the application is built. • In ASP.NET it must be named web.config. You might define one in different sub folders, but the security part (authentification e.g.) must be in the root folder of the site.

  23. .config fil and ADO.NET • Example of SQLExpress connection string: <?xmlversion="1.0" encoding="utf-8" ?> <configuration> <configSections> </configSections> <connectionStrings> <addname="TestConnection" connectionString="Data Source=pcm06463\sqlexpress;Initial Catalog=dbtest; User ID=test;Password=" providerName="System.Data.SqlClient" /> </connectionStrings> </configuration> Internal name Database Machine name Nessesary for sqlexpress

  24. Get provider and connection string • From ConfigurationManager: .... string provider = ConfigurationManager.ConnectionStrings["TestConnection"].ProviderName; string connStr = ConfigurationManager.ConnectionStrings["TestConnection"].ConnectionString; ..... Example: \ReaderWithConfig Example: \ReaderWithConfig2

  25. Parameters in SQL statements • Makes it possible to use the same SQL-statement in multible situations. • But harder to debugge string sqlString = "INSERT INTO datotest Values (@dato)"; SqlParameter sqlParam = new SqlParameter("@dato", System.Data.SqlDbType.DateTime); sqlParam.Value = DateTime.Now; SqlCommand comm = _conn.CreateCommand(); comm.CommandText = sqlString; comm.Parameters.Add(sqlParam); int result = comm.ExecuteNonQuery(); ExecuteNonQuery is used for insert, delete and update

  26. Transaction - Definition UCN T&B - CBH (FEN) Databases/Transactions • A transaction is an operation on data in the database. • A transaction may be composed of several database operations, but is viewed as a logical unit of work • A transaction must be done completely or not done at all • A transaction must have the ACID properties: • A: Either it is done in total or it is not done at all (Atomicity) • C: The database moves from one consistent state to an other consistent state (Consistency) • I: If more operations are accessing the same data, they are not to disturb each other – they must execute as if they executed alone (Isolation) • D: When a transaction completes, its changes to the database are permanent (Durability)

  27. time Transactions – example:T1 and T2 are executing concurrently Any possible problems? T1: Transfers N DKKs from account X to account Y: read_item(X); X:= X-N; write_item(X); read_item(Y); Y:= Y+N; write_item(Y); T2: Deposits M DKK on account Y: read_item(Y); Y:= Y+M; write_item(Y);

  28. Transactions – Problems • We want several transactions to execute concurrently (Why?) • Three types of problems: • lost update • uncommitted dependency (temporary update) • inconsistent analysis (incorrect summary) • Crash during execution of a transaction must be handled

  29. Lost Update

  30. Uncommitted Dependency

  31. Inconsistent Analysis

  32. Transactions • In C#: Bank Transactions Example: demos\Transactions\BankTransaction1

  33. Multiple Databases • Moving from (badly designed) database to another (better designed) database: Example: demos\flytDataApp

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