Lecture 11: Programmatic Database Access with ADO.NET

11-2 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Objectives “Programmatic database access typically involves executing SQL queries using classes from the language's framework. In.NET, the Active Data Objects (ADO) classes in the FCL are the primary means of database programming. ADO.NET is a vendor-neutral, object-oriented, SQL-based approach…” Architecture of ADO.NET Basic database access Application design Updating a database DataSets

11-3 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Part 1 Architecture of ADO.NET…

11-4 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Relational technology ADO.NET is designed to access relational databases Example: –Sales database with customers, orders, and products

11-5 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Architecture ADO.NET architecture based on data providers –data providers encapsulate DB-specific details Data Provider ADO.NET.NET Programmer DB

11-6 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Existing data providers.NET currently ships with 4 data providers: –one for Microsoft SQL Server –one for Oracle –one for older OLEDB technology (used for ADO, VB6) –one for older ODBC (Open Database Connectivity) technology More third-party providers are available… –Oracle's own provider: –DB2: –MySQL: –etc.

11-7 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET ADO.NET object model ADO.NET is an object-oriented approach Classes are spread across a number of FCL namespaces –some are provider-neutral, others are provider-specific SQL Server System.Data.Common System.Data System.Data.SqlClient System.Data.OleDb other DBs, e.g. MS Access provider-neutral ODBC (Open Database Connectivity) System.Data.Odbc

11-8 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Part 2 Basic database access…

11-9 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Overview of database access Three steps: 1.open connection to database 2.execute SQL to retrieve records / update DB 3.close connection

11-10 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET import System.Data.*; import System.Data.OleDb.*; String sConnection; sConnection = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=Sales.mdb"; OleDbConnection dbConn; dbConn = new OleDbConnection(sConnection); dbConn.Open(); MessageBox.Show(dbConn.get_State().toString()); import System.Data.*; import System.Data.OleDb.*; String sConnection; sConnection = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=Sales.mdb"; OleDbConnection dbConn; dbConn = new OleDbConnection(sConnection); dbConn.Open(); MessageBox.Show(dbConn.get_State().toString()); (1) Open connection Connections are opened based on connection string info –here we open a connection to a MS Access 2000 database –"Sales.mdb" must exist in same dir as.EXE (e.g. bin\Debug) connection

11-11 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Building connection strings Connection strings are vendor-specific Connection strings are not well-documented Where to turn for help? – –

11-12 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET (2) Retrieve records Retrieve records via SQL Select query –read-only access via DataReader & field names String sql, fn, ln; Customer c; sql = "Select * From Customers Order By LastName Asc, FirstName Asc;"; OleDbCommand dbCmd; OleDbDataReader dbReader; dbCmd = new OleDbCommand(sql, dbConn); dbReader = dbCmd.ExecuteReader(); while ( dbReader.Read() ) // retrieve records one-by-one… { fn = String.valueOf(dbReader.get_Item("FirstName")); ln = String.valueOf(dbReader.get_Item("LastName")); c = new Customer(fn, ln); this.listBox1.get_Items().Add(c); } String sql, fn, ln; Customer c; sql = "Select * From Customers Order By LastName Asc, FirstName Asc;"; OleDbCommand dbCmd; OleDbDataReader dbReader; dbCmd = new OleDbCommand(sql, dbConn); dbReader = dbCmd.ExecuteReader(); while ( dbReader.Read() ) // retrieve records one-by-one… { fn = String.valueOf(dbReader.get_Item("FirstName")); ln = String.valueOf(dbReader.get_Item("LastName")); c = new Customer(fn, ln); this.listBox1.get_Items().Add(c); } data reader record field name of data value in current record command connection

11-13 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET (3) Close connection Be sure to close reader and connection… –to flush pending updates (in general) –so others can access DB (connections are limited resources) dbReader.Close(); dbConn.Close(); dbReader.Close(); dbConn.Close();

11-14 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Part 3 Data-driven application design…

11-15 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Data Tier design Recall N-Tier design… GUI.exe DataAccess import System.Data.*; import System.Data.OleDb.*; public class DataAccess { private String sConnection; public DataAccess(String filename) { this.sConnection = String.Format("Provider=...;Data Source={0}{1}", System.AppDomain.get_CurrentDomain().get_BaseDirectory(), filename); } public java.util.ArrayList getCustomers() throws System.Exception {. } import System.Data.*; import System.Data.OleDb.*; public class DataAccess { private String sConnection; public DataAccess(String filename) { this.sConnection = String.Format("Provider=...;Data Source={0}{1}", System.AppDomain.get_CurrentDomain().get_BaseDirectory(), filename); } public java.util.ArrayList getCustomers() throws System.Exception {. }

11-16 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Guaranteed close? Ensure reader / DB closed via try-catch-finally pattern –and *note* that we want to catch.NET System.Exception objects, not Java java.lang.Exception objects… OleDbConnection dbConn = null; OleDbDataReader dbReader = null; try { dbConn = new OleDbConnection(…); dbConn.Open();. } catch(System.Exception ex) { System.Diagnostics.Debug.WriteLine("DB error: " + ex.get_Message()); throw new System.Exception("Data Error!", ex); } finally { // always executes whether we succeed or throw exception… if (dbReader != null) dbReader.Close(); if (dbConn != null) dbConn.Close(); } OleDbConnection dbConn = null; OleDbDataReader dbReader = null; try { dbConn = new OleDbConnection(…); dbConn.Open();. } catch(System.Exception ex) { System.Diagnostics.Debug.WriteLine("DB error: " + ex.get_Message()); throw new System.Exception("Data Error!", ex); } finally { // always executes whether we succeed or throw exception… if (dbReader != null) dbReader.Close(); if (dbConn != null) dbConn.Close(); }

11-17 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Part 4 Updating a database…

11-18 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Executing action queries Use action queries when you need to modify a DB –updates –inserts –deletes Execute action queries via ExecuteNonQuery method…

11-19 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Basic idea Open, execute, and close: String sConnection, sql; sConnection = "..."; sql = "..."; OleDbConnection dbConn; OleDbCommand dbCmd; dbConn = new OleDbConnection(sConnection); dbCmd = new OleDbCommand(sql, dbConn); int rows; dbConn.Open(); rows = dbCmd.ExecuteNonQuery(); // returns # of rows affected… dbConn.Close(); if (rows != 1) // sanity check to make sure it worked... throw new System.Exception("Query ran but failed to update DB?!"); String sConnection, sql; sConnection = "..."; sql = "..."; OleDbConnection dbConn; OleDbCommand dbCmd; dbConn = new OleDbConnection(sConnection); dbCmd = new OleDbCommand(sql, dbConn); int rows; dbConn.Open(); rows = dbCmd.ExecuteNonQuery(); // returns # of rows affected… dbConn.Close(); if (rows != 1) // sanity check to make sure it worked... throw new System.Exception("Query ran but failed to update DB?!");

11-20 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Dynamic SQL Most of the time you'll need to build SQL dynamically –i.e. based on input values from the user Example: –delete the selected customer… String fn, ln; Customer c; c = this.listBox1.get_SelectedItem(); fn = c.firstName; ln = c.lastName; sql = "..."; String fn, ln; Customer c; c = this.listBox1.get_SelectedItem(); fn = c.firstName; ln = c.lastName; sql = "...";

11-21 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Dynamic string building Dynamic SQL requires dynamic string building Example: –build dynamic SQL to delete selected customer… –don't forget the delimiters for strings & dates! String sql; sql = String.Format("Delete From Customers Where " + "FirstName='{0}' And LastName='{1}';", fn, ln); String sql; sql = String.Format("Delete From Customers Where " + "FirstName='{0}' And LastName='{1}';", fn, ln);

11-22 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Example Delete selected customer… private void listBox1_SelectedIndexChanged(…) { String fn, ln, sql; int rows; Customer c; c = (Customer) this.listBox1.get_SelectedItem(); if (c == null) return; // nothing selected… fn = c.firstName; ln = c.lastName; sql = String.Format("Delete From Customers Where " + "FirstName='{0}' And LastName='{1}';", fn, ln);. dbConn.Open(); rows = dbCmd.ExecuteNonQuery(); // delete! dbConn.Close(); if (rows != 1) throw new System.Exception("Query ran but failed to delete?!"); this.listBox1.get_Items().Remove(c); // update GUI! MessageBox.Show("Deleted!"); } private void listBox1_SelectedIndexChanged(…) { String fn, ln, sql; int rows; Customer c; c = (Customer) this.listBox1.get_SelectedItem(); if (c == null) return; // nothing selected… fn = c.firstName; ln = c.lastName; sql = String.Format("Delete From Customers Where " + "FirstName='{0}' And LastName='{1}';", fn, ln);. dbConn.Open(); rows = dbCmd.ExecuteNonQuery(); // delete! dbConn.Close(); if (rows != 1) throw new System.Exception("Query ran but failed to delete?!"); this.listBox1.get_Items().Remove(c); // update GUI! MessageBox.Show("Deleted!"); }

11-23 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Oops! Try to delete "O'Dahl, Kathie"… What happens?

11-24 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Escaping delimiters Most common DB programming mistake: –forgetting to escape delimiter characters… Solution? –just replace ' with 2 in a row, i.e. ' ' private void listBox1_SelectedIndexChanged(…) { String fn, ln, sql; int rows; Customer c; c = (Customer) this.listBox1.get_SelectedItem(); if (c == null) return; // nothing selected… fn = c.firstName; ln = c.lastName; fn = fn.Replace("'", "''"); ln = ln.Replace("'", "''"); sql = String.Format("Delete From Customers Where " + "FirstName='{0}' And LastName='{1}';", fn, ln); private void listBox1_SelectedIndexChanged(…) { String fn, ln, sql; int rows; Customer c; c = (Customer) this.listBox1.get_SelectedItem(); if (c == null) return; // nothing selected… fn = c.firstName; ln = c.lastName; fn = fn.Replace("'", "''"); ln = ln.Replace("'", "''"); sql = String.Format("Delete From Customers Where " + "FirstName='{0}' And LastName='{1}';", fn, ln);

11-25 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Part 5 DataSets…

11-26 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET DataSets DataSets are an in-memory data structure –easily filled with data from a database –easily passed around –easily displayed in a GUI app DataSet Name Price Stock Ants $ Birds $ Cats $ Dogs $ DB Command Connection DataAdapter DataSet mirrors the database –data forms a temporary table called "Table" within DataSet "Table"

11-27 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Filling a DataSet DataAdapter object is used to fill a DataSet… Example: –fill DataSet with all product data sql = "Select * From Products Order By Name Asc;";. DataSet ds; OleDbDataAdapter adapter; ds = new DataSet(); adapter = new OleDbDataAdapter(dbCmd); dbConn.Open(); adapter.Fill(ds); dbConn.Close(); sql = "Select * From Products Order By Name Asc;";. DataSet ds; OleDbDataAdapter adapter; ds = new DataSet(); adapter = new OleDbDataAdapter(dbCmd); dbConn.Open(); adapter.Fill(ds); dbConn.Close(); "Table" Name Price Stock Ants $ Birds $ Cats $ Dogs $

11-28 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET DataGrid display DataSet can be bound to DataGrid control for easy display –one line of code!. this.dataGrid1.SetDataBinding(ds, "Table");. this.dataGrid1.SetDataBinding(ds, "Table");

11-29 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET DataGrid is a powerful control By default, DataGrid is read/write –user can modify data –user can add rows –user can delete rows However, all changes are local to DataSet –to flush changes back to DB, reconnect and update…

11-30 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Flushing changes back to database Reconnect, and apply adapter's Update() method –use CommandBuilder object to generate necessary SQL for you // retrieve existing data set from grid… ds = (DataSet) this.dataGrid1.get_DataSource();. OleDbCommandBuilder cmdBuilder; cmdBuilder = new OleDbCommandBuilder(adapter); dbConn.Open(); adapter.Update(ds); // this will throw exception if update(s) conflict… dbConn.Close(); // retrieve existing data set from grid… ds = (DataSet) this.dataGrid1.get_DataSource();. OleDbCommandBuilder cmdBuilder; cmdBuilder = new OleDbCommandBuilder(adapter); dbConn.Open(); adapter.Update(ds); // this will throw exception if update(s) conflict… dbConn.Close();

11-31 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Summary Databases are a critical component of most business apps SQL is the standard programming language for databases Database programming is based on framework classes –in.NET, those classes are called ADO.NET –the more you know about SQL the better