The Problems HTTP is disconnected So many database vendors Create a simple consistent versatile interface on the data Look at ADO.NET classes OleDb SQL server optimised

ADO.NET Classes System.Data.OleDb.OleDbConnection The connection object is used to create a connection between our code and the database. System.Data.OleDb.OleDbCommand Used to store a command to be applied to the database. May be either raw SQL or a stored procedure. System.Data.OleDb.OleDbParameter Used to model parameters passed to the stored procedures / queries. System.Data.OleDb.OleDbDataAdapter Used to fill a data table with the results of a command.

ADO.NET Classes Continued System.Data.DataTable Used to model data obtained from the database. Data Readers We are also going to take a look at data readers even though they are not used on the module.

Connected v Disconnected Data The need for locking… User A opens a record User B opens the same record and makes changes User B saves the changes on the record User A makes their changes to the record User A now saves their changes and overwrites the changes made by User B Relatively easy to lock records on a local area network

Disconnected Data When a client application access a record it communicates with the server via the HTTP request. The server locates and processes the data returning it to the client at which point the connection is lost. User A opens a record on the browser, the server locks the record to stop User B accessing it User B tries to access the record and is presented with a message stating that the record is locked User A is in the middle of editing the record and his browser crashes thus not telling the server he is done with the record User B sits there waiting and waiting for the record to come free!

Add a Time – Out? User A opens the record and goes and makes a cup of tea The lock times out User B opens the record What does User A do with their data when the save the changes? I am not planning on exploring solutions to these problems, simply to bring your attention to them.

OleDb v SQL Optimised Classes OleDB is a technology devised by Microsoft for connecting to a wide range of database management systems (DBMS), e.g. Access, Oracle MySQL. SQL optimised classes perform in exactly the same way as the OleDB classes but fine tuned to work with SQL server.

Usage OleDb OleDbConnection connectionToDB = new OleDbConnection (); SQL SqlConnection connectionToDB = new SqlConnection(); The classes also have different namespace... using System.Data.SqlClient; and using System.Data.OleDb;

The Execute Function

The Connection Object connectionToDB = new OleDbConnection(connectionString);

DSN / DSN(less) Connections DSN = Data Source Name The database may be file on the disk (the way that we have been connecting to the database in this module!) (DSN(less)) Or the database may be running on a server with an IP address on a specific port number (remember TCP/IP allows a program on one computer to talk to another!) (DSN)

Data Providers DBMS specific driver

Connection Strings Contains DBMS specific configuration data Specifies the data provider //open the database connectionToDB.Open();

The Command Object Applies a “Command” to the data Initialise with stored procedure name and connection //initialise the command builder for this connection OleDbCommand dataCommand = new OleDbCommand(SProcName, connectionToDB); Add parameters //loop through each parameter for (int Counter = 0; Counter < SQLParams.Count; Counter += 1) { //add it to the command object dataCommand.Parameters.Add(SQLParams[Counter]); } Set the Command Type //set the command type as stored procedure dataCommand.CommandType = CommandType.StoredProcedure;

So far…

The Mincing Machine

Data Adapter Initialisation //set the select command property for the data adapter dataChannel.SelectCommand = dataCommand; Filling the Data Table //fill the data adapter dataChannel.Fill(queryResults);

Data Tables Select * from tblAddress To reference “Nottingham” in our code we would do the following... AnAddress.Town = queryResults.Rows[3]["Town"].ToString();

Data Readers Read-only, forward-only stream of data Faster and more light weight than data tables Lock the data so may have problems with multiple connections One way flow of data

Example