c#: introduction for developers
DESCRIPTION
Neal Stublen [email protected]. C#: Introduction for Developers. Tonight’s Agenda. Database Errors Parameterized queries ToolStrip control Master-detail relationships Custom data objects IDisposable ADO.NET connections Q&A. Dataset Review. Review. - PowerPoint PPT PresentationTRANSCRIPT
Tonight’s Agenda
Database Errors Parameterized queries ToolStrip control Master-detail relationships Custom data objects IDisposable ADO.NET connections Q&A
DATASET REVIEW
Review
How would you display a single customer record on a form?
CHAPTER 18, PART 3
HANDLING DATA ERRORS
Database Errors
Errors can be reported by the data provider, ADO.NET, or a bound control
Possible causesInvalid dataNetwork failureServer shutdown
Data Provider Errors
Data providers will throw an exception when an error occursSqlExceptionOracleExceptionOdbcExceptionOleDbException
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 Exceptionprivate 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 DatasetDBConcurrencyExceptionDataException (general exception)ConstraintExceptionNoNullAllowedException
Message property describes the exception
Catch ADO.NET Exceptiontry{ 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 eventExceptionRowIndexColumnIndex
Catch DataGridView Errorsprivate void gridView_DataError(...){ // report error in e.RowIndex and/or // e.ColumnIndex}
CHAPTER 19
MORE WITH DATA SOURCES AND DATA SETS
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 optionsNumeric valuesDates
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
AddNewAdd a new blank row to the data source
EndEditSave changes to a new or existing row
CancelEditAbort and changes to a new or existing row
RemoveCurrentDelete the current row
Using a BindingSource
Position/CountDetermine current position with the data
source MoveFirst MoveLast MoveNext MovePrevious
Change the current position within the data source
CHAPTER 19, PART 2
PARAMETERIZED QUERIES
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 with @
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 “LIKE @Name” Drag Customers table onto a form Update Fill to append ‘%’ (wildcard) ToolStrip is added to provide the
@Name parameter Examine Fill button’s Click event
CHAPTER 19, PART 3
TOOLSTRIPS
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 stripCancelEdit() on the customersBindingSource
Navigation Tool Strip
A ToolStrip can be used to add and update rows in the data sourcecustomersBindingSource.AddNew();customersBindingSource.EndEdit();customersBindingSource.CancelEdit();customersBindingSource.RemoveCurrent();
CHAPTER 19, PART 4
MASTER-DETAIL RELATIONSHIPS
DataViewGrid Control
Smart tag allows you to modify commonly used properties
Columns can be added, moved, or removedRemove ID columnsColumns 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
CHAPTER 20
CREATING DATA ACCESS OBJECTS
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 CommandsSqlCommand 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 = @State
@State is a SQL variable representing the state
Create the ParametersSqlParameter stateParam = new SqlParameter();stateParam.ParameterName = "@State";stateParam.Value = some_local_variable;
cmd.Parameters.Add(stateParam);
cmd.Parameters.AddWithValue("@State", 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 CommandsSqlDataReader r = cmd.ExecuteReader();
List<Customer> customers =new List<Customer>();
while (r.Read()){ Customer c = new Customer(); ... customers.Add(c);}
r.Close();cxn.Close();
Other Commandsobject result = cmd.ExecuteScalar();// Cast result to expected type
cmd.ExecuteNonQuery();
Chapter 20-1 Exercise
MMABooksDB CustomerDB
GetCustomer – ExecuteReader, exceptionsAddCustomer – current IDUpdateCustomer – concurrency,
ExecuteNonQuery StateDB
Notice exception handling frmAddModifyCustomer
Notice DataSource for states
BONUS CONTENT
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 Connectionsusing (SqlConnection cxn = ...){ cxn.Open(); using (SqlCommand cmd = ...) { cmd.Execute... }}
Using Equivalenceusing (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
http://msdn.microsoft.com/en-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?
http://blogs.msdn.com/b/dotnet/archive/2012/10/18/an-easy-solution-for-improving-app-launch-performance.aspx
http://msdn.microsoft.com/en-us/magazine/cc163655.aspx
http://msdn.microsoft.com/en-us/library/cc656914(v=vs.110).aspx
CHAPTER 24
MENUS, TOOL BARS, AND STATUS BARS
Designer Walkthrough
Summary
MenuStrip w/ defaults ToolStrip w/ defaults StatusStrip View Menu Toggles PerformClick() ToolStripContainer w/ docking ContextMenuStrip SplitContainer ErrorProvider