SQL Server Database Web Applications

Transcription

1 SQL Server Database Web Applications Microsoft Visual Studio (as well as Microsoft Visual Web Developer) uses a variety of built-in tools for creating a database-driven web application. In addition to the SQL Server database, there are programming elements which might be written in Visual C# or some other language, page content mixed with HTML-style and actual HTML tags, and in-line Structure Query Language which are SQL statements embedded into the code. Also Visual Studio is able to manipulate a wide variety of other database types including Microsoft Access, Oracle, etc. Start by selecting NewWeb Site from the File menu to create a new ASP.NET Web Site. The New Web Site dialog window opens in which Visual C# should be selected from the Installed Templates and ASP.NET Empty Web Site should be selected as the project type. Browse to find the Save location for the website and give it a name, e.g. PremiereWebsite which is the name given to the folder below that will contain the files for the site. (In this course you simply will download the existing "Premiere Products" website from the instructor's website and "Open" it.)

2 SQL Server Database Web Applications Page 2 Master Pages An ASP.NET Master Page is a single document that allows for a consistent layout for all the pages in an ASP.NET Web Site. When the individual content pages for the Web site are created, they contain the content you want to display. When users request an actual Web page, the Master Page is merged with the content page to produce output that combines the Master Page layout with the content. To create a new Master Page: 1. Right-click the project name on the second line in the Solution Explorer window 2. Select Add New Item from the drop-down menu 3. Select Master Page from the Template pane of the Add New Item dialog window 4. Enter a name for the new Master Page (if the.master extension is not entered, it will be added automatically by Visual Web Developer) 5. Click the <Add> button to create the new Master Page The Master Page can be linked to a Web page when a new Web Form is created (this will be discussed later in this lesson). In this course we will not actually be learning to create Master Pages. You either will be given a Master Page file to copy into the website or code to copy and paste into the Master Page. CSS (Cascading Style Sheets) A Cascading Style Sheet (CSS) is a list of statements (or rules ) that can format various HTML elements. It is a component that is common to all HTML documents and not unique to Visual Studio alone. Style rules can be specified for multiple Web pages all at once from a single Style Sheet document. The functioning of the Style Sheet is similar to that of master pages in that these rules are collected and merged thereby formatting the Web document when it is opened (this also will be discussed later in this lesson). To create a new Style Sheet: 1. Right-click the project name on the second line in the Solution Explorer window 2. Select Add New Item from the drop-down menu 3. Select Style Sheet from the Template pane of the Add New Item dialog window 4. Enter a name for the new Style Sheet (if the.css extension is not entered, it will be added automatically by Visual Web Developer) 5. Click the <Add> button to create the new Style Sheet Again in this course we will not be learning to create Style Sheets. In this course you either will be given a Style Sheet file or code to copy and paste into the Style Sheet.

3 SQL Server Database Web Applications Page 3 Web Forms Web Forms are the central component of an ASP.NET application. They provide all the content of a Web page. Additionally through the program code (e.g. Visual C#) they provide the dynamic content that allows the Web document to connect to and interact with a database. When the Web Form is requested, it is converted into an HTML document (a Web page) to be viewed in a browser (e.g. Microsoft Internet Explorer, Mozilla Foxfire, Opera, etc.). To create a new Web Form: 1. Right-click the project name on the top line in the Solution Explorer window 2. Select Add from the drop-down menu 3. Select Add New Item from the "Add" sub-menu 4. Select Web Form from the Template pane of the Add New Item dialog window 5. Enter a name for the new Web Form (if the.aspx extension is not entered, it will be added automatically by Visual Studio) 6. Set any other options for the Web Form by clicking the CheckBoxes on or off 7. Click the <Add> button to create the new Web Form The CheckBox Place code in separate file allows the developer to place the Visual C# code into a separate file with the extension aspx.cs. In simpler Web applications like those we are doing for this course, we will keep the code in the same file to make it easier to find, so leave this CheckBox unchecked.

4 SQL Server Database Web Applications Page 4 As mentioned before, the Master Page can be linked to the new Web Form when it first is created. If the Select master page CheckBox was set on (see Add New Item dialog window image on previous page) prior to clicking the <Add> button, the Select a Master Page dialog window opens. Click the Master Page that is to be linked to the Web Form and then click the <OK> button. This also might be the time to link the Web Form to a Style Sheet. To do this select the command Attach Style Sheet from the Format menu. In the Select Style Sheet dialog window select the Project folder that contains the style sheet. The from the Contents of folder window select the name of the style sheet and click the <OK> button.

5 SQL Server Database Web Applications Page 5 The GridView Control One way to insert content onto the page might be by coding. However because the Visual Studio IDE (integrated development environment) interface is a GUI (graphical user interface) application, there are alternate ways content can be placed on the page more easily. Notice that there are three tabs at the lower-left of the IDE window, [Design], [Split], and [Source]. Make certain that the [Design] tab is clicked to work with the GUI interface. The GridView control is a powerful tool for displaying data from a DataSource. For purposes of this course a ldatasource (which actually is also a control in Visual Studio) is a table or SQL query (View) from a SQL Server database. The data from the database is displayed in a grid of rows and columns similar to a spreadsheet. Each row in the grid is one of the records from the table. Each column is data from one of the fields with the fieldname displayed in the first row. The simplest way to create a new GridView on a Web Form is to drag the table or query icon from Server Explorer directly onto the Web Form document. When a Web Form with a GridView control is executed, the table data is displayed without the need to perform any other configuration operations other than what was just specified. There are additional GridView elements that are configurable. Click on the control and click the smart tag button ( ) at the upper-right corner of the control. The GridView Tasks dialog window opens. Click on the following checkboxes to: 1. Enable Paging which creates numbered button in the GridView to advance to other pages for longer tables (e.g. click the page number to go to a specific page) 2. Enable Sorting which enables sorting by any field in the table (click the column name heading at the top of any column to sort on that field; click a second time on the same column name to sort in descending sequence)

6 SQL Server Database Web Applications Page 6 3. Enable Editing which creates an <Edit> button that allows users to update records directly in the GridView control (after clicking <Edit>, click either the displayed <Update> button to make the changes to a record or the <Cancel> button to cancel any updates) 4. Editing Deleting which creates a <Delete> button that allows users to delete records directly from the GridView control To configure the visual appearance of the GridView, click on the Auto Format command in the GridView Tasks dialog window. From the Auto Format dialog window Select a scheme, Preview it and click the <OK> button.

7 SQL Server Database Web Applications Page 7 Another characteristic of this control that can be set is its horizontal alignment (it can be centered on the Web Form). Click on the GridView, scroll to HorizontalAlign in the Properties window, click the arrow for the property and select Center from the dropdown list. One of the advantages of creating a GridView control this way is that a number of related processes are completed automatically including the configuration of the SQLDataSource control (which also appears on the Web Form in design view but is not in the rendered Web page) and the creation of the ConnectionString. The ConnectionString is needed when trying to connect to the database when writing programming code in Visual C# in the Code Editor (more about this later). Running a Visual Studio ASP.NET Application Running an application created in Visual Studio means to view it in a Web browser (e.g. Internet Explorer, Firefox, Chrome, etc.) and to interact with its functionality. To view and test a Web Form application, begin by clicking the Start Debugging button on the Standard toolbar. The Debugging Not Enabled dialog window will display the first time a user runs a new Web application. Accept the default answer Modify the Web.config file to enable debugging since you are debugging the application and click the <OK> button.

8 SQL Server Database Web Applications Page 8 At this point if there are no errors in the Web Form, a new Web browser window will open and the page will be rendered so that it can be viewed. Test the elements of the page and when finished close the browser window. Designing Web Forms Now create another Web Form named NewRep.aspx. Make certain that the [Design] tab is clicked to work with the GUI interface. To develop Web Forms actual text simply can be typed onto the page. Additionally other visual elements such as TextBoxes, Buttons and Labels can be inserted by selecting them from the Toolbox (see the example below). Use the buttons on the Formatting toolbar to format elements on the Web Form using font, text color, alignment, etc. Unlike standard Visual C# desktop projects, controls from the Toolbox cannot be placed on the Web Form wherever you want them. The elements on the page flow from left to right, and top to bottom, as they are inserted much like when using a word processor. Pressing the <Enter> key doublespaces to the beginning of the next line. Absolute positioning of elements on the page requires more know-how than we have time for this course.

9 SQL Server Database Web Applications Page 9 Visual Controls, the Toolbox and the Properties Window The Visual Web Developer Toolbox, usually docked inside the left edge of the IDE window, displays icons which represent the visual elements that can be inserted onto the Web Form. Click the mouse on the Toolbox tab and it pops out from the edge of the window. Each icon can be dragged and dropped onto the development page. The TextBox is a control that lets users viewing your Web page type information into the page. Click on the control in the Toolbox (found in the Standard group or section) and drag it onto the Web Form. There are handles at the right and bottom of the control that can be dragged to resize it. In a Web application the text typed into the TextBox might be used as field information in a new or updated record. The Button control is used to display a push button that is clicked by the user. It may either be a submit button that submits page information back to the server or a command button. If it is a command button, it will be associated with a specific event such as the Click event. In this case, when the user clicks it, it executes the statements written by the developer in an Event handler coded in either Visual Basic or Visual C# (more on this later). A Label control allows the developer to place unattached text on the Web Form. Its Text property specifies the text that is displayed. Characteristics of the visual controls are known as its properties. The two most important properties for most controls are the ID and Text properties. The ID property actually is a name (its identifier) given to the control (in fact in Visual Studio Windows desktop applications it is called the Name property). Whenever referring to the control in the Code Editor, the developer must use its ID property. The Text property is a text label that appears on, in, or near the control.

10 SQL Server Database Web Applications Page 10 A control s properties are updated in a window known as the Properties window located in the lower right area of the Visual Studio IDE. Properties may be arranged in alphabetical ( ) order or categorized ( ) together in related groups (there are two buttons near the top of the Properties window to choose between these two options). Because of its importance, the ID property is the first one in the list when they are listed alphabetically. Type the updated property value in the textbox to the right of the property name to update it. There are some properties in which the property value instead may be selected from a drop-down list of valid values. Also there are other properties that have an ellipse [ ] button at the end of the line; when the button is clicked, a dialog window opens with a number of options for selecting the property value. The ID properties for the TextBoxes in the NewRep Web Form are: RepNumTextBox LastNameTextBox FirstNameTextBox AddressTextBox CityTextBox StateTextBox ZipTextBox CommissionTextBox RateTextBox The properties for the Button control in the NewRep Web Form are: ID: SubmitTextBox Text: Submit Finally the properties for the Label control below the Button in the NewRep Web Form are: ID: ErrorMessageLabel Its Text property should be blank

11 SQL Server Database Web Applications Page 11 Another useful property for TextBoxes is the MaxLength property. The MaxLength controls the number of characters that can be typed into a TextBox. By default the value for this property is set to zero (0) which means there is no limit to the number of characters typed. For SQL Server VARCHAR fields, it can be useful to limit the maximum number of characters entered into a TextBox to match the length of the VARCHAR field in SQL Server. For each TextBox type this value on the MaxLength line in the Properties window. The MaxLength properties for the TextBoxes in the NewRep Web Form are: RepNumTextBox: 2 LastNameTextBox: 15 FirstNameTextBox: 15 AddressTextBox: 30 CityTextBox: 15 StateTextBox: 2 ZipTextBox: 5 Validation Controls ASP.NET validation controls are used to validate user input. If the data entered into an input control on the Web page is invalid according to a validation rule specified in a validation control, an error message will be displayed. A variety of these controls are found in the Toolbox in the Validation group. The RegularExpressionValidator validates that user input for a field matches a specified pattern. The developer can create a string that represents the pattern, although these strings can be rather complex and confusing. However the cool thing about this control is that many common patterns already are built into it. Some of these patterns include Internet addresses and URL s, phone numbers, ZIP codes and Social Security numbers.

12 SQL Server Database Web Applications Page 12 To select a built-in pattern, add a RegularExpressionValidator control to the Web Form; it usually will be positioned just to the right of the control it is validating such as a TextBox. Select the control and find the ValidationExpression property in the Properties window. Click the ellipse [ ] button and the dialog window opens. Select one of the Standard expressions and click the <OK> button. Or a ValidationExpression string can be typed directly into the textbox (in this course any string that needs to be typed will be given to you by the instructor). Two other properties also should be set for all validation controls. The ErrorMessage property is a text message that will display if the validation fails. The ControlToValidate property is the ID (name) of the control that is being validated by this validation control. In the Properties window click the arrow at the end of the line for this property and select the valid control ID from the drop-down list. Another useful validation control is the RequiredFieldValidator. Validation for this control fails if the input value does not change from its initial value, usually an empty string. The ErrorMessage and ControlToValidate properties are they same for this as for all validation controls. A third validation control is the RangeValidator control which lets the developer specify minimum and maximum allowable values. The additional properties for this validator are MinimumValue and MaximumValue (the range), as well as Type which specifies the data type being validated, e.g. String, Integer, Double, Date or Currency. The ValidationSummary control displays a summary of the error messages generated for all the validation controls when the page is submitted. In this case the individual messages do not display within the separate validation controls but rather are collected and displayed in this single location, often at the top or bottom of the Web Form. The validation controls and properties for the NewRep Web Form are: ID: RepNumRequiredFieldValidator ControlToValidate: RepNumTextBox Display: Dynamic ErrorMessage: ID number may not be blank ForeColor: Red

13 SQL Server Database Web Applications Page 13 ID: RepNumRegularExpressionValidator ControlToValidate: RepNumTextBox ErrorMessage: ID number must be 2 digits ForeColor: Red ValidationExpression: \d2 ID: LastNameRequiredFieldValidator ControlToValidate: LastNameTextBox ErrorMessage: Last name may not be blank ForeColor: Red ID: FirstNameRequiredFieldValidator ControlToValidate: FirstNameTextBox ErrorMessage: First name may not be blank ForeColor: Red ID: StreetRequiredFieldValidator ControlToValidate: StreetTextBox ErrorMessage: Street address may not be blank ForeColor: Red ID: CityRequiredFieldValidator ControlToValidate: CityTextBox ErrorMessage: City may not be blank ForeColor: Red ID: StateRequiredFieldValidator ControlToValidate: StateTextBox Display: Dynamic ErrorMessage: State may not be blank ForeColor: Red ID: StateRegularExpressionValidator ControlToValidate: StateTextBox ErrorMessage: State must be two uppercase letters ForeColor: Red ValidationExpression: ^[A-Z]2 ID: ZipRequiredFieldValidator ControlToValidate: ZipTextBox Display: Dynamic ErrorMessage: Zip code may not be blank ForeColor: Red

14 SQL Server Database Web Applications Page 14 ID: ZipRegularExpressionValidator ControlToValidate: ZipTextBox ErrorMessage: Zip code must be 5 digits ForeColor: Red ValidationExpression: \d5 (the same as a French postal code) ID: CommissionRegularExpressionValidator ControlToValidate: CommissionTextBox ErrorMessage: Commission must be numeric ForeColor: Red ValidationExpression: ^\d+(\.\d+)?$ ID: RateRangeValidator ControlToValidate: RateTextBox ErrorMessage: Rate must be between 0.00 and 0.20 ForeColor: Red MaximumValue: 0.20 MinimumValue: 0.20 Type: Double

15 SQL Server Database Web Applications Page 15 The Button Control and Event Handling An event handler is a method (sometimes called a function) that executes when it receives a message (the event) from a device such as the mouse or keyboard. The default event for a Button control is the Click event which occurs when the Button is clicked. The method is a block of code that executes whenever the event (the click ) occurs. Format: protected void ControlName_Event (object sender, EventArgs e) (The code that executes when the event occurs goes here) To create an event handler for a Button located on a Web Form, double-click the Button. A new method is created automatically in the Source window (you can always click the <Design> tab to get back to that window). The method name consists of the name of the object (e.g. SubmitButton in the example below) and the event (e.g. Click in this example) that results in its execution. It is positioned inside an HTML <script> block, where both server-side and client-side program code is located in an HTML document. The image above shows a new (but yet to be completed) method that has just been inserted into the Source window. An example of the completed method appears on the next page. The method executes whenever the Button named SubmitButton located on the NewRep Web Form is clicked by a user. The various commands within the example method will be the topic of discussion for the remainder of this tutorial.

16 SQL Server Database Web Applications Page 16 <script runat="server"> Sample Button Click Event Method: SubmitButton_Click protected void SubmitButton_Click(object sender, EventArgs e) SqlDataSource PremiereDataSource = new SqlDataSource(); PremiereDataSource.ConnectionString = ConfigurationManager.ConnectionStrings["PremiereConnectionString1"]. ConnectionString; PremiereDataSource.InsertCommandType = SqlDataSourceCommandType.StoredProcedure; PremiereDataSource.InsertCommand = "InsertRep"; PremiereDataSource.InsertParameters.Add("RepNum", RepNumTextBox.Text); PremiereDataSource.InsertParameters.Add("LastName", LastNameTextBox.Text); PremiereDataSource.InsertParameters.Add("FirstName", FirstNameTextBox.Text); PremiereDataSource.InsertParameters.Add("Street", StreetTextBox.Text); PremiereDataSource.InsertParameters.Add("City", CityTextBox.Text); PremiereDataSource.InsertParameters.Add("State", StateTextBox.Text); PremiereDataSource.InsertParameters.Add("Zip", ZipTextBox.Text); PremiereDataSource.InsertParameters.Add("Commission", CommissionTextBox.Text); PremiereDataSource.InsertParameters.Add("Rate", RateTextBox.Text); int rowseffected = 0; try rowseffected = PremiereDataSource.Insert(); catch (Exception ex) ErrorMessageLabel.Text = ex.message; ; finally PremiereDataSource = null; if (rowseffected!= 0) Server.Transfer("Rep.aspx"); </script> (Whenever the symbol appears in the code above, it is an indication that a statement is continued on the next line. Most importantly in Visual C# programming never press the <Enter> key in the middle of a string.)

17 SQL Server Database Web Applications Page 17 SqlDataSource Class The SqlDataSource control provides the functionality for accessing and managing the data in relational databases. When a GridView control is created by dragging a table from a SQL Server database onto a Web Form, a related SqlDataSource control is created automatically and placed onto the form. Although the control appears on the Web Form in Design View in Visual Web Developer, the SqlDataSource is not visible in the rendered Web page when it is viewed in a browser window. A new SqlDataSource object variable is declared ( instantiated ) in one of the first statements in a method that inserts a record into the SQL Server database table. This is a coded object, not visual one. Format: SqlDataSource SqlDataSourceObjectVariableName = new SqlDataSource(); In the statement above the name SqlDataSource is used in C# is the data type (or more properly type because it is an object variable) of the variable created The keyword new instantiates the new variable and makes it an object so that the object variable name PremiereDataSource below can be used throughout the rest of the SubmitButton_Click method Example: SqlDataSource PremiereDataSource = new SqlDataSource();

18 SQL Server Database Web Applications Page 18 The ConnectionString Property and the Web.config File Additionally when the GridView control is created by dragging a table from a SQL Server database onto the Web Form, another benefit was the automatic creation of a ConnectionString. The connection string stores the path and filename information for the database. Additionally it indicates which type of database the data source control accesses (e.g. SQL Server, Oracle, etc.). This connection string was inserted automatically into the Web.config file which appears in the Solution Explorer window (double-click on the filename to view the file). The ConnectionString name given in the Web.config file provides an easy and flexible way of assigning the SqlDataSource.ConnectionString property to provide access to a relational database. Format: SqlDataSourceObjectVariableName.ConnectionString = ConfigurationManager.ConnectionStrings["connectionString"].ConnectionString(); ConfigurationManager.ConnectionStrings class returns a connection object from the connectionstring name The ConnectionString() method returns the specific connection string from the Web.config file Example: PremiereDataSource.ConnectionString = ConfigurationManager.ConnectionStrings["PremiereConnectionString1"]. ConnectionString(); Note that the string PremiereConnectionString1 is the same as the connectionstring name in the Web.config file.

19 SQL Server Database Web Applications Page 19 InsertCommand and InsertCommandType Properties The InsertCommandType property is a method of class SqlDataSource. The two valid values for the property, which comes from the SqlDataSourceCommandType class, indicate that the type for the subsequent InsertCommand is one of the following: 1. Text text contained in the corresponding command is an actual SQL INSERT command string 2. StoredProcedure text contained in the corresponding command comes from a previously created SQL Server stored procedure Format: SqlDataSourceObjectVariableName.InsertCommandType = SqlDataSourceCommandType.CommandType; The valid CommandType values are Text and StoredProcedure, both members of the SqlDataSourceCommandType class Example: PremiereDataSource.InsertCommandType = SqlDataSourceCommandType.Text; The InsertCommand property, also a member of class SqlDataSource, contains a SQL INSERT command (either a text string or a stored procedure name) that will be executed by the Insert() method. Format: SqlDataSourceObjectVariableName.InsertCommand = "INSERT INTO tablename (fieldnamelist) VALUES (parameterlist)" The tablename is the name of the table in the SQL Server database The fieldnamelist are the names of the fields in the SQL Server database table The parameterlist is a list of variables that hold the values to be written into the new record (this topic will be explained in the next section) Example: PremiereDataSource.InsertCommand = "INSERT INTO Rep (RepNum, LastName, FirstName, Street, City, State, Zip, Commission, Rate)

20 SQL Server Database Web Applications Page 20 Alternately if the InsertCommandType is set to StoredProcedure as per the example below... PremiereDataSource.InsertCommandType = SqlDataSourceCommandType.StoredProcedure;... the developer can name a SQL Server database StoredProcedure that previously created that exists in Server Explorer e.g as the InsertCommand. Parameters PremiereDataSource.InsertCommand = "InsertRep"; Parameter objects are variables that hold the data that will be inserted into a parameterized SQL statement. The InsertParameters.Add() method for a parameter collection creates the parameter variable and associates it with the source from where the data will be retrieved such as the Text property of a TextBox. Format: SqlDataSourceObjectVariableName.InsertParameters.Add("parameterName", datasource); The parametername is a name given to the parameter variable within the parameter collection (customarily the same name as the fieldname although not mandatory) The datasource is the location within the application or the system from which the data to be stored in the parameter variable will be retrieved; it could be the Text property of a TextBox or some other element identified from within the system (e.g. the date and time as represented by the expression DateTime.Now() or the IP address of the server that submitted the data represented by the expression Request.UserHostAddress). Example: PremiereDataSource.InsertParameters.Add("RepNum", RepNumTextBox.Text);

21 SQL Server Database Web Applications Page 21 The Insert() Method The Insert() method, a member of the class SqlDataSource, executes the InsertCommand and inserts the new record into the SQL Server database table. It returns an integer which indicates how many records were added to the table (should be just one record). Format: SqlDataSourceObjectVariableName.Insert(); Example: rowseffected = PremiereDataSource.Insert(); The variable rowseffected is assigned an integer which is the number of records added to the table (should always be just one in all our examples in this class) Try Catch Exception Processing The C# try catch structure is a cleaner and more elegant way of handling run-time errors that occur during program execution. This is especially important for the type of errors that could result in a program crash. Such a situation technically is known as throwing an exception (do not be overly concerned about that terminology in this course) and often results in a rather ugly error message that appears in the browser window from which the average user has no way of recovering. A simple try catch structure consists of three parts: 1. The try block which contains the executable statements that have the possibility of generating a run-time error 2. The catch block which executes only when a run-time error occurs; it might contain a statement that displays an error message or it could transfer to a Web page that contains the error message or some instructions on how to proceed next 3. The finally block which contains statements that should execute after try catch processing completes whether or not the run-time error occurs Format: try (Executable statements that could result in a run-time error) catch (Exception exceptionvariable) (Statements that execute if a run-time error does occur) finally (Statements that execute if a run-time error occurs or not)

22 SQL Server Database Web Applications Page 22 Example: try rowsaffected = PremiereDataSource.Insert(); catch (Exception ex) ErrorMessageLabel.Text = ex.message; finally PremiereDataSource = null; The Server.Transfer Method The Server.Tranfer() method opens a new Web page in the browser window. Format: Server.Transfer("URL"); The URL is the Web address of the new Web page Example: The null Object Server.Transfer("Rep.aspx"); Assigning the object value null to an object destroys the object and makes it available for handling by the operating system s garbage collector. It is a good habit to destroy objects that no longer are needed in an application Format: SqlDataSourceObjectVariableName = null; Example: PremiereDataSource = null;