C#: INTRODUCTION

FOR DEVELOPERS

Neal Stublennstublen@jccc.edu

DATABASE CHECK

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 SourceView > Server ExplorerAdd Connection...Server name: .\SQLEXPRESSDatabase name: MMABooksTest Connection

HANDLING DATA ERRORS

Data Provider Errors SqlException OracleException OdbcException OleDbException

Number Message Source Errors

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 DBConcurrencyException DataException ConstraintException NoNullAllowedException

Message

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}

DataGridView Control Errors Not an exception, but an event on the

control

DataError

Exception RowIndex ColumnIndex

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

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

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 “LIKE @Name” Drag Customers table onto a form Update Fill to append ‘%’ ToolStrip is added to provide the @Name 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 stripCancelEdit() 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

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 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

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

Using Our Own ConnectionsSqlConnection 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;SqlReader 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 let this happen…

string cmd = "SELECT * FROM Customers WHERE State=" + value;

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();

Examine Chapter 20 Code MMABooksDB CustomerDB

GetCustomer – ExecuteReader, exceptionsAddCustomer – current IDUpdateCustomer – concurrency,

ExecuteNonQuery StateDB frmAddModifyCustomer

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();}