ADO.Net CS795

What is ADO.Net? Database language spoken by managed applications ADO.net database accesses go through modules: data providers –SQL Server.Net provider---to interface with MS SQL databases without any help from unmanaged providers –OLE DB.Net provider---to interface with other databases through unmanaged OLE DB providers OLE DB providers provide a uniform API over a variety of databases

System.Data.SqlClient using System.Data.SqlClient … SqlConnection conn = new SqlConnection (“server=(local); Initial Catalog = database=pubs; uid=mukka; pwd=“); Or (“server=(local); Initial Catalog = database=pubs; Trusted_Connection=Yes;“); try { conn.Open(); SqlCommand cmd = new SqlCommand(“select * from titles”, conn); SqlDataReader reader = cmd.ExecuteReader (); while (reader.Read ()) Console.Writeln (reader[“title”]); } Catch (SqlException ex) {Console.WriteLine (ex.message); } finally {conn.Close();} Note: For OLEDB, simply replace Sql in the above code by OleDb

Connections, Commands, DataReaders The canonical usage pattern for executing database commands in ADO.Net: 1.Create a connection object encapsulating a connection string 2.Open the connection by calling Open on the connection object 3.Create a command object encapsulating both an SQL command and the connection that the command will use 4.Call a method on the command object to execute the command 5.Close the connection by calling Close on the connection object

SqlConnection Class SqlConnection = conn SqlConnection(); Conn.ConnectionString = “server=localhost; database=pubs; uid=mukka; pwd=“; Or SqlConnection conn = “server=localhost; database=pubs; uid=mukka; pwd=“; Other parameters for ConnectionString: x It can also be defined on web.config: The constructor of the SqlConnection object expects one parameter: the connection string. The connection string identifies the SQL server name, the SQL database name, and satisfies the authorization requirement by providing a user name and a password, or by specifying Trusted_Connection=true. You can specify the connection string in line within the constructor line, or you can specify it in Web.config:

Open and Closing Connections You must first open a connection and close it at the end. SqlConnection conn = new SqlConnection (“server=localhost; database=pubs; uid=mukka; pwd=“); try{ conn.Open(); ….} catch (SqlConnection ex){ …..} finally { conn.Close();}

Command Classes ExecuteReader (for read) ExecuteNonQuery (for updates) SqlConnection conn = new SqlConnection (“server=localhost; datbase=pubs; uid=mukka; pwd=“); try { conn.Open(); SqlCommand cmd = new SqlCommand (); cmd.CommandText= “delete from title where title_id = “xxxx”; cmd.Connection = conn; cmd.ExecuteNonQuery (); } catch (SqlException ex) { ….} finally { conn.Close();}

ExecuteNonQuery To execute operations where database is changed Example: insert, update, delete, create database, create table, etc. Insert, update, delete: Returns number of rows affected by the operation Returns -1 for others SqlCommand cmd = new SqlCommand (“insert into titles (title_id, title, type, pubdate)”+ “values (‘CS150’,’C++ Programming’,” + “ ‘computer science’, ‘May 2006’), conn); cmd.ExecuteNonQuery();

ExecuteScalar Returns the 1 st row of the 1 st column in the result Used for commands such as: count, avg, min, max, sum try{ conn.Open(); SqlCommand cmd = new SqlCommand (“select max (advance) from title”, conn); decimal amount = (decimal) cmd.ExecuteScalar (); Console.WriteLine (“ExecuteScalar returned (0:c)”, amount); } Catch (SqlException ex} {Console.Writeln (ex.Message);} finally {conn.Close();}

ExecuteScalar (cont.) To retrieve BLOBs (Binary large objects) from databases FileStream stream new FileStream (“Logo.jpg”, FileMode.Open); byte[] blob new byte [stream.Length]; stream.Read (blob, 0, (int) stream.Length); stream.Close(); SqlConnection con = new … try{ conn.Open(); SqlCommand cmd = new SqlCommand (“insert into pub_info (pub_id, logo) values conn); cmd.Parameters.Add blob); cmd.ExecuteNonQuery (); } catch … finally …

ExecuteScalar (Cont.) To validate a user name and password (page , Jeff Prosie book) Try { conn.Open(); StringBuilder builder = new StringBuilder (); builder.Append (“select count (*) from users where username = …. int count = (int) command.ExecuteScalar (); return (count > 0); }

ExecuteReader Method To perform database queries Returns a DataReader object: SqlDataReader or OleDataReader try{ conn.Open(); SqlCommand cmd = new SqlCommand(“select * from titles”, conn); SqlDataReader reader = cmd.ExecuteReader(); While (reader.Read()) Console.WriteLine (reader[“title”]); } ****************** try {conn.Open(); SqlCommand cmd = new SqlCommand(“select * from titles”, conn); SqlDataReader reader = cmd.ExecuteReader(); for (int i=0; i <reader.FieldCount; i++) Console.WriteLine (reader.GetName[i])); } reader.Close();

Transactions Ex: transfer funds from one account (say 1234) to another account (say 9876). SqlTransaction trans = null; SqlConnection conn = new SqlConnection (“server=localhost; database=mybank; uid=mukka; pwd=“); try{conn.Open(); trans = conn.BeginTransaction (IsolationLevel.Serializable); SqlCommand cmd = new SqlCommand(); cmd.Connection = conn; cmd.Transaction=trans; cmd.CommandText = “update accounts set balance = balance-1500 where account_id = ‘1234’ “; cmd.ExecuteNonQuery(); cmd.CommandText = “update accounts set balance = balance+1500 where account_id = ‘9876’ “; cmd.ExecuteNonQuery(); Trans.Commit(); } Alternate to Commit is Rollback.

Parameterized Commands When commands are the same but the parameters are different Try{ conn.Open(); SqlCommand cmd = new SqlCommand(“update accounts set balance = balance”+ where account_id conn); cmd.Parameters.Add SqlDbType.Money); cmd.Parameters.Add SqlDbType.Char); = -1500; = “1234”; cmd.ExecuteNonQuery (); = 1500; = “9867”; cmd.ExecuteNonQuery (); }

Stored Procedures User defined command added to a database Execute faster because they are already in compiled form. CREATE PROCEDURE char char (10); AS BEGIN TRANSACTION UPDATE Accounts SET Balance = Balance WHERE Account_ID IF = 0 BEGIN ROLLBACK TRANSACTION RETURN END UPDATE Accounts SET Balance = Balance WHERE Account_ID IF = 0 BEGIN ROLLBACK TRANSACTION RETURN END COMMIT TRANSACTION GO

How does an application call the stored procedure? SqlConnection conn = new SqlConnection (“server=localhost; database=mybank; uid=mukka; pwd=“); try{conn.Open(); SqlCommand cmd = new SqlCommand (“proc_TransferFunds”, conn); cmd.CommandType = CommandType.StoredProcedure; cmd.Parameters.Add 1500); cmd.Parameters.Add ‘1234’); cmd.Parameters.Add ‘9876’); cmd.ExecuteNonQuery (); } Catch (SqlException ex) { ….} finally {conn.Close(); }

Example where it returns a value CREATE PROCEDURE money OUTPUT AS =Balance From Accounts WHERE Account_ID IF = 1 RETURN 0 ELSE BEGIN = 0 RETURN -1 END GO ***************** SqlConnection conn = new SqlConnection (“server=localhost; database=mybank; uid=mukka; pwd=“); try{conn.Open(); SqlCommand cmd = new SqlCommand (“proc_GetBalance”, conn); cmd.CommandType = CommandType.StoredProcedure; cmd.Parameters.Add ‘1234’); SqlParameter bal = cmd.Parameters.Add SqlDbType.Money); bal.Direction = ParameterDirection.Output; SqlParameter ret = cmd.Parameters.Add SqlDbType.Int); ret.Direction = ParameterDirection.ReturnValue; cmd.ExecuteNonQuery (); int retval = (int) ret.value; decimal balance = (decimal) bal.Value; } catch (SqlException ex) { ….} finally {conn.Close(); }

DataSet Class DatasetDatabase DataTableTable DataRowRecords in a DataTable DataColumnFields in a DataTable DataSet.Tables DataTabe.Rows DataTable.Columns UniuqeConstraintAdd a contsraint to a column DataRelationRelationship between two tables

Dataset (cont.) Datasets are ideal for retrieving results from database queries and storing them in memory. In addition, this data may be modified and propagated back to the database. It can also support, random access to the data (unlike DataReader) Great for caching, especially in web applications.

DataSets vs. DataReaders If the application simply queries a database and reads through the records one at a time until it finds the record it is looking for, DataReader is the right tool If the application requires all results from a query, say to display in a table, and have ability to iterate back and forth through the result set, DataSet is a good alternate.

DataAdapter DataSets don’t interact with databases directly; Instead, they interact through DataAdapters Purpose: To perform database queries and create DataTables containing the query results; also, to write the modified DataTables into databases Fill and Update

DataAdapter.Fill SqlDataAdapter adapter = new SqldataAdapter (“select * from titles”, “server=localhost; database=pubs; uid=mukka; pwd=“); DataSet ds = new dataSet (); adapter.Fill (ds, “Titles”); What does Fill do? (1)Open a connection to the pubs database using adapter. (2)Performs a query on the pubs database using the query string passed to adapter. (3)Creates a DataTable named “Titles” in ds. (4)Initializes DataTable with a schema that matches that of the “Titles” table in the database. (5)Retrieves records produced by the query and writes them to the DataTable (6)Closes the connection to the database

DataTable foreach (DataTable table in ds.Tables) Console.WriteLine (table.TableName); DataTable table = ds.Tables[0]; foreach (DataRow row in table.Rows) Console.WriteLine(row[0]); DataTable table = ds.Tables[0]; foreach (DataRow row in table.Rows) Console.WriteLine(row[“account_id”]); DataTable table = ds.Tables[0]; foreach (DataColumn col in table.Columns) Console.WriteLine(“Name={0}, Type ={1}”, col.ColumnName, col.DataType);

Insert a record into DataTable SqlDataAdapter adapter = new SqldataAdapter (“select * from titles”, “server=localhost; database=pubs; uid=mukka; pwd=“); DataSet ds = new dataSet (); adapter.Fill (ds. “Titles”); DataTable table ds.Tables[“Titles”]; DataRow row = table.NewRow (); row[“title_id”] = “CS795”; row[“title”] = “.Net Security”; row[“price”]=“70.99”; Table.Rows.Add (row);

Propagating Changes back to Database SqlDataAdapter adapter = new SqldataAdapter (“select * from titles”, “server=localhost; database=pubs; uid=mukka; pwd=“); SqlCommandBuilder builder = new SqlCommandBuilder (adapter); DataSet ds = new dataSet (); adapter.Fill (ds. “Titles”); DataTable table ds.Tables[“Titles”]; DataRow row = table.NewRow (); row[“title_id”] = “CS795”; row[“title”] = “.Net Security”; row[“price”]=“70.99”; table.Rows.Add (row); adapter.Update (table); (only writes the ones that were changed)

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Links The C# Station ADO.NET Tutorial Using ADO.NET for beginners In Depth ASP.NET using ADO.NET