Neal Stublen

Populating a Database  SQLExpress should be installed with Visual Studio  The book provides a.sql file for populating the MMABooks database in SQLExpress  Double-click the.bat file on the S: drive  We’ll need to repeat this process at the start of each class session

Confirm Database Access  Using Visual Studio to locate the new database as a Data Source View > Server Explorer Add Connection... Server name:.\SQLEXPRESS Database name: MMABooks Test Connection

Data Provider Errors  SqlException  OracleException  OdbcException  OleDbException  Number  Message  Source  Errors

Catch Provider Exception private void Form1_Load(object sender, EventArgs e) { try { this.customersTableAdapter.Fill(...); } catch (SqlException ex) { // report ex.Number, ex.Message }

ADO.NET Errors  DBConcurrencyException  DataException  ConstraintException  NoNullAllowedException  Message

Catch ADO.NET Exception try { this.customerBindingSource.EndEdit(); this.customersTableAdapterManager.UpdateAll(...); } catch (DBConcurrencyException ex) { // from UpdateAll() exception // report concurrency error this.customerTableAdapter.Fill(...); } catch (DataException ex) { // from EndEdit() exception // report ex.Message customerBindingsSource.CancelEdit(); } catch (SqlException ex) { // report ex.Number, ex.Message }

DataGridView Control Errors  Not an exception, but an event on the control  DataError  Exception  RowIndex  ColumnIndex

Catch DataGridView Errors private void gridView_DataError(...) { // report error in e.RowIndex and/or // e.ColumnIndex }

Dataset Designer  Command property on Fill, GetData  Opens Query Builder  Visually build SQL command  Preview Data to see query results

Designer.cs Queries  SQL queries are updated in the schema’s Designer.cs file  DeleteCommand, InsertCommand, UpdateCommand  SCOPE_IDENTITY() = ID generated from INSERT command = query parameter  UPDATE only updates a record matching original column values

Bound TextBox Controls  Formatting and Advanced Binding  Select TextBox  Open Properties Window  Expand DataBindings property  Select Advanced option, click “…”  Select new format type  Specify representation of null value

Bound ComboBox Controls  Populate a ComboBox with values from a column of a database table  SelectedItem is used to specify the value in a column of another database table

Code Practice  Select customer state using dropdown list ComboBox instead of TextBox  Create StatesDataSet in Data Source window  Add DataSet control for StatesDataSet and set DataSetName property  Add BindingSource control for DataSet and set DataSource/DataMember properties  Set State field to use ComboBox  Set ComboBox to use data bound controls  Clear ComboBox data bindings for Text property

Parameterized Queries  We can customize a DataSet by providing parameters to modify the query  Parameters can be introduced using the Query Builder

Code Practice  Create a customer search form  Populate a DataGridView based on the entry within a TextBox  Create CustomersDataSet as a Data Source  Open CustomersDataSet.xsd and modify Fill CommandText using Query Builder  Change Name Filter to  Drag Customers table onto a form  Update Fill to append ‘%’  ToolStrip is added to provide parameter  Examine Fill button’s Click event

What was that ToolStrip?  A tool strip can be docked around the main window  It contains other controls  Controls can be added through the Items collection  Items have events just like other controls  We can add a “Cancel” button to the navigation tool strip CancelEdit() on the customersBindingSource

Navigation Tool Strip  customersBindingSource.AddNew();  customersBindingSource.EndEdit();  customersBindingSource.CancelEdit();  customersBindingSource.RemoveCurrent();  A binding source keeps all bound controls in sync

DataViewGrid Control  Smart tag allows you to modify commonly used properties  Columns can be added, moved, or removed Remove ID columns Columns still exist in the DataSet  Column content can be formatted using DefaultCellStyle

Master-Detail Relationships  One-to-many relationship between tables  One customer has many invoices

Code Practice  View customer invoices based on the selection of a customer record  Populate DataGridView with invoice entries  Create Customers-Invoices DataSet  Customers uses Detail View  Drag Customers onto Form  Drag Customers.Invoices onto Form  Examine DataSource/DataMember on grid view and invoicesBindingSource

Why create our own?  Place data objects into a shared library  We’re not using a form  Separates database code from UI code

Using Our Own Connections SqlConnection cxn = new SqlConnection(); cxn.ConnectionString = "..."; cxn.Open();... cxn.Close(); Sample Connection String: Data Source=localhost\SqlExpress; Initial Catalog=MMABooks; Integrated Security=False; User ID=Be Careful; Password=Be Very, Very Careful;

Using Our Own Commands SqlCommand cmd = new SqlCommand(); cmd.CommandText = "SELECT * FROM Customers"; cmd.CommandType = CommandType.Text; cmd.Connection = cxn; SqlReader r = cmd.ExecuteReader();

Parameters in Commands  Add parameters to SQL statements SELECT * FROM Customers WHERE STATE = 'VA' SELECT * FROM Customers WHERE STATE is a SQL variable representing the state

Create the Parameters SqlParameter stateParam = new SqlParameter(); stateParam.ParameterName = stateParam.Value = some_local_variable; cmd.Parameters.Add(stateParam); value);

SQL Injection  Don’t let this happen… string cmd = "SELECT * FROM Customers WHERE State=" + value;

Executing Commands SqlDataReader r = cmd.ExecuteReader(); List customers = new List (); while (r.Read()) { Customer c = new Customer();... customers.Add(c); } r.Close(); cxn.Close();

Other Commands object result = cmd.ExecuteScalar(); // Cast result to expected type cmd.ExecuteNonQuery();

Examine Chapter 20 Code  MMABooksDB  CustomerDB GetCustomer – ExecuteReader, exceptions AddCustomer – current ID UpdateCustomer – concurrency, ExecuteNonQuery  StateDB  frmAddModifyCustomer

Disposable Objects  IDisposable interface  Single method: Dispose()  Releases unmanaged resources that may be held by an object  Such as a database connection!!

Using…  using keyword can be used to confine objects to a particular scope  using also ensures that Dispose() is called if the object implements IDisposable  using also calls Dispose if an exception is thrown

Disposable Connections using (SqlConnection cxn =...) { cxn.Open(); using (SqlCommand cmd =...) { cmd.Execute... }

Using Equivalence using (object obj = …) { } object obj = …; try { } finally { obj.Dispose(); }