Neal Stublen

Tonight’s Agenda  Database Errors  Parameterized queries  ToolStrip control  Master-detail relationships  Custom data objects  IDisposable  ADO.NET connections  Q&A

Review  How would you display a single customer record on a form?

Database Errors  Errors can be reported by the data provider, ADO.NET, or a bound control  Possible causes Invalid data Network failure Server shutdown

Data Provider Errors  Data providers will throw an exception when an error occurs SqlException OracleException OdbcException OleDbException

Error Properties  Number  Message  Source  Errors Contains multiple errors that may have occurred when executing a single command Number and Message refer to the first error in the collection

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  Errors may occur when updating a Dataset DBConcurrencyException DataException (general exception) ConstraintException NoNullAllowedException  Message property describes the exception

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 }

Concurrency Errors  Exception handling of concurrency errors may be tested by running multiple instances of an application and editing the same record from both applications

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

Formatting Bound Text  Advanced formatting options Numeric values Dates  Display for null values  Format and Parse events of the Binding object

Why a BindingSource?  Using a BindingSource will keep all bound controls synchronized  Changing the position within a data source will update all the bound controls  Changes made to any controls will update the data source when changing position

Using a BindingSource  AddNew Add a new blank row to the data source  EndEdit Save changes to a new or existing row  CancelEdit Abort and changes to a new or existing row  RemoveCurrent Delete the current row

Using a BindingSource  Position/Count Determine current position with the data source  MoveFirst  MoveLast  MoveNext  MovePrevious Change the current position within the data source

Parameterized Queries  We can customize a DataSet by providing parameters to modify the query  Add Query from smart tag menu of a bound control  Parameters can be introduced by modifying the WHERE clause  Parameter values are prefixed

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 ‘%’ (wildcard)  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  A ToolStrip can be used to add and update rows in the data source customersBindingSource.AddNew(); customersBindingSource.EndEdit(); customersBindingSource.CancelEdit(); customersBindingSource.RemoveCurrent();

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 customer entries  Populate DataGridView with invoice entries  Create CustomerInvoice 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  Start with an empty console application

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; SqlDataReader 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 do this… string cmd = "SELECT * FROM Customers WHERE Name=" + value;  Especially if value is user-entered data, such as: “John; DROP TABLE Customers;”

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();

Chapter 20-1 Exercise  MMABooksDB  CustomerDB GetCustomer – ExecuteReader, exceptions AddCustomer – current ID UpdateCustomer – concurrency, ExecuteNonQuery  StateDB Notice exception handling  frmAddModifyCustomer Notice DataSource for states

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(); } }

Open/Close Connections  ADO.NET uses “connection pooling” to optimize opening and closing connections to the database  cxn.Open() and cxn.Close() are using connections from the connection pool that share the same connection string  ADO.NET manages the actual connection to the database  us/library/8xx3tyca(v=vs.110).aspx us/library/8xx3tyca(v=vs.110).aspx

Think of it like this… class SqlConnectionPool { public SqlConnection Open(string cxnStr) { if (mPool.Contains(cxnString)) { return mPool[cxnString]; } // Create a new connection... }

And… class SqlConnectionPool { public void CheckIdle() { foreach (cxn in mPool) { if (cxn.IsIdle()) { cxn.ReallyClose(); mPool.Remove(cxn); }

DataSets in Class Libraries  Create a DataSet in a class library  Specify DataSet Modifier property public or internal?  Add the library as a reference from another project  Select “Referenced DataSets” when adding a DataSet control to a form  Add a BindingSource  Add form controls and bind them to the BindingSource

Slow Start Times?  012/10/18/an-easy-solution-for- improving-app-launch-performance.aspx 012/10/18/an-easy-solution-for- improving-app-launch-performance.aspx  us/magazine/cc aspx us/magazine/cc aspx  us/library/cc656914(v=vs.110).aspx us/library/cc656914(v=vs.110).aspx

Designer Walkthrough

Summary  MenuStrip w/ defaults  ToolStrip w/ defaults  StatusStrip  View Menu Toggles  PerformClick()  ToolStripContainer w/ docking  ContextMenuStrip  SplitContainer  ErrorProvider