Next strMessage.Append(Footer) Return strMessage.ToString Else Return “” End If End Function ‘ ‘ Provides access to the list of errors that were detected ‘ during the validation process. This is used for applications ‘ that need custom error messages. ‘ Public ReadOnly Property ValidationErrors() As ArrayList Get Return m_arrErrors End Get End Property ‘ ‘ Indicates whether any validation errors were detected ‘ as the data was stored into the object. ‘ Public ReadOnly Property IsValid() As Boolean Get Return (m_arrErrors.Count = 0) End Get End Property End Class Listing 2.5 BaseServices.vb (continued) Let’s go through each part of the BaseServices class so that you understand what each method and property is doing for the derived classes. Writing the Class Declarations The BaseServices class itself is defined as shown: Public MustInherit Class BaseServices The MustInherit keyword indicates that this class cannot be created. The only place that we can use this class is as a base class for other classes. Thus, other classes that inherit it can use the services provided by this class. The next part is an ArrayList variable defined as follows: Private m_arrErrors As ArrayList Contact Manager Application 47 The variable is declared as Private since we aren’t going to access it directly outside of this class or any derived classes; instead, you’ll create a property procedure to access it from this class. Private variables are not available in derived classes; instead, you have to access them using properties also located in the base class. Write the Class Methods and Properties The BaseServices class provides important functionality to the business object classes you will build later in this project. It knows how to communicate with the database so that we don’t have to write the same tedious code repeatedly as we build the various classes. We’re using a number of new features included in the .NET Framework to handle database activity, so let’s go through each method in more detail now. New Constructor The New constructor is designed to be overloaded. In other words, a derived class that inherits BaseServices can use this base method in addition to its own implementation of the constructor. For instance, this constructor expects to receive a Database object and a SQL statement. In cases where there isn’t already an existing database connec- tion, the derived class will need to create one. In addition, the derived class will need to have a SQL statement so that we can connect to the proper table. Since this base class will be used for a variety of other classes, we don’t want anything specific to one type of data in it. The first object that we instantiate is the SqlDataAdapter object. The SqlDataAdapter is designed to make it easier to deal with SQL Server databases. In Project 1, you wrote quite a bit of code to make your database activity work properly. You wrote a Select statement, an Insert statement to add new rows, an Update statement to make changes, and a Delete statement to remove records. When you stop to think about it, each one of those statements could have been generated automatically as long as you knew the pri- mary key of the table. The SqlDataAdapter does just that. When you create or instanti- ate the object, you give it a SQL statement as well as a SqlConnection object. The SQL statement you provide here is known as the SelectCommand and is stored in that prop- erty of the object. Since this statement includes the primary key, we can use the next object to do a little magic. The SqlCommandBuilder object performs many of the tasks that ASP programmers, including myself, had done in previous versions of ASP. It looks at the SqlDataAdapter object, determines the structure of the table being used, and then automatically builds the Insert, Delete, and Update statements necessary to manage the table. In addition, it registers itself to listen for any events generated by the SqlDataAdapter that indicate data changes are taking place. When we call the Update method of the SqlDataAdapter, the SqlDataAdapter looks through the DataSet object (which we’ll talk about next) and determines what rows have been added, modified, or deleted since the last save. It then generates events that the SqlCommandBuilder listens for in order to send the appropri- ate SQL statements. The end result is that you make all your changes in the DataSet and call the Update method of the SqlDataAdapter to make all the changes for you. It saves 48 Project 2 a lot of work and a lot of tedious code writing in which you populate a long SQL state- ment or a long list of parameters for a SqlCommand object. The DataSet object is another new object in .NET and is roughly equivalent to a record set in old Active Data Objects. However, it does have some distinct differences, the key one being that a DataSet object is not tied to any particular type of database. There isn’t a SqlDataSet or OleDBDataSet object—just a DataSet object. A DataSet object has the ability to store multiple tables of data. Each of these tables is a DataTable object, containing a Rows collection; each Row is a DataRow object. We’ll be manipu- lating DataRow objects when we want to save the data. These DataRows are stored in the DataTable and DataSet objects. The DataSet object is fed back into the Sql- DataAdapter to make the changes permanent. We’ll be covering many of the features of the DataSet object in this book, but for more information, refer to the MSDN docu- mentation on this object as well as the rest of the data objects. If you’d like a good book on the new ADO.NET, check out Programming ADO.NET by Richard Hundhausen and Steven Borg (John Wiley & Sons, 2002). GetRow Function The DataSet object that we’ll keep in memory will have either zero rows or one row in it at any time. For cases where we don’t instantiate the derived class with a primary key ID, we’re going to add a new row, and the GetRow function will return an empty row that we can then fill up. For cases where we did provide a primary key, the con- structor selected that row from the database and populated it into the DataSet object. We simply return that single row to the caller so that it can be edited. SaveRow Function The derived class will overload this routine, but this base class function does handle some key tasks and has to be called by the derived class. First of all, it accepts a DataRow object containing either a new record or a modified copy of the current record. For new records, the DataRow is simply added to the DataSet. Modified records are a little harder since we can’t just store the DataRow into the DataSet. Instead, we take the fields from the copy and put them into the original one in the DataSet using a loop. The derived class will then need to call any other validation or other code that needs to be run once this step is complete. Data Validation Utilities All the derived classes will have validation code in them verifying data before we attempt to store it in the database. The DataSet object is useful; however, it doesn’t pre- vent you from putting potentially bad data into it. In addition, there are cases in which we have custom validation that involves more than one field at a time. The derived class is responsible for its own validation, but the BaseServices class provides some utilities to make it easier. Before validation starts, the derived class can reset the error list by calling the ClearErrors method, which eliminates any past errors. As errors are detected during Contact Manager Application 49 validation, the derived class can call the AddError method. This method accepts a string as input and stores the string in the private variable called m_arrErrors. This ArrayList accumulates all the collected errors as the validation continues. Once the validation routine is complete, the derived class has a few options for dis- playing the error. The ValidationError function allows the errors to be returned in a variety of formats. The ValidationError function accepts a string as input for the header of the error message, a format string for each validation error that was detected, and a string for the footer of the message. The default format for the error message looks something like this: The following errors were detected in your data: - error message 1 - error message 2 You can easily supply other information for the default (and optional) parameters to this function. This routine can also be used to generate HTML lists of various sorts, or even JavaScript, with a little bit of extra work. The last feature provided here is a simple property called IsValid that returns a True if no errors are in the validation error array. This provides a quick check for any calling code before it attempts to save data permanently. The point behind these features is to provide services to the base classes. The base class does not force anything to happen, such as throwing an exception if an error is stored, although it could. I prefer to build the object with features that I can use in a logical method elsewhere. Build the Person Class The first class we’ll build in this project that deals specifically with data is the Person class. It will use the BaseServices class as its base class and build functionality on top of that. The Person class will: ■■ Allow code to create either a new object of this type or pass in a primary key for a person to load from the database. ■■ Make the existing data available or allow a new row to be added to the table. ■■ Validate the data before saving it to the database. ■■ Provide a list of error messages applicable to the object’s data. ■■ Save the new or updated record to the database. The complete listing for the Person class is shown in Listing 2.6. Because the class code is quite lengthy, we’ll work through each logical chunk one at a time. Imports AtWorkUtilities Imports System.Data.SqlClient Public Class Person Inherits BaseServices Listing 2.6 Person.vb Class 50 Project 2 ‘ ‘ If no arguments are supplied, build a separate ‘ database connection for this object. ‘ Public Sub New() MyBase.New(New Database(), “SELECT * FROM tblPeople WHERE 1=0”) End Sub ‘ ‘ If database connection is supplied, store it ‘ in the private connection variable for this ‘ object. ‘ Public Sub New(ByVal db As Database) MyBase.New(db, “SELECT * FROM tblPeople WHERE 1=0”) End Sub ‘ ‘ If both database and ID are supplied, retrieve ‘ data into the object from the database. ‘ Public Sub New(ByVal db As Database, _ ByVal ID As Integer) MyBase.New(db, “SELECT * FROM tblPeople WHERE pkPersonID = “ _ & ID.ToString) End Sub ‘ ‘ Verify that all data validation rules have been ‘ met. Any errors get stored into the errors collection ‘ inherited from the BaseServices class. ‘ Public Sub Validate() Dim dr As DataRow ClearErrors() For Each dr In m_DS.Tables(0).Rows If dr.RowState = DataRowState.Added _ Or dr.RowState = DataRowState.Modified Then ValidateRow(dr) End If Next End Sub ‘ ‘ Checks an individual row for validation rule ‘ compliance. Any errors are added to the errors Listing 2.6 Person.vb Class (continued) Contact Manager Application 51 ‘ collection. ‘ Private Sub ValidateRow(ByVal dr As DataRow) If IsDBNull(dr(“CompanyName”)) And _ IsDBNull(dr(“LastName”)) And _ IsDBNull(dr(“FirstName”)) Then AddError(“You must provide the company name, “ _ & “the person’s first or last name.”) End If If Not IsDBNull(dr(“CompanyName”)) And _ Not IsDBNull(dr(“LastName”)) And _ Not IsDBNull(dr(“FirstName”)) Then If dr(“CompanyName”) = “” _ And dr(“LastName”) = “” _ And dr(“FirstName”) = “” Then AddError(“You must provide the company name, “ _ & “the person’s first or last name.”) End If End If If Not IsDBNull(dr(“LastName”)) Then If dr(“LastName”).Length > 40 Then AddError(“Last name must be less than 40 characters long.”) End If End If If Not IsDBNull(dr(“FirstName”)) Then If dr(“FirstName”).Length > 40 Then AddError(“First name must be less than 40 characters long.”) End If End If If Not IsDBNull(dr.Item(“Title”)) Then If dr(“Title”).Length > 80 Then AddError(“Title must be less than 80 characters long.”) End If End If If Not IsDBNull(dr.Item(“Title”)) Then If dr(“CompanyName”).Length > 80 Then AddError(“Company name must be less than 80 characters long.”) End If End If If Not IsDBNull(dr.Item(“Title”)) Then If dr(“Address”).Length > 240 Then AddError(“Address must be less than 240 characters long.”) Listing 2.6 Person.vb Class (continued) 52 Project 2 TEAMFLY Team-Fly ® End If End If If Not IsDBNull(dr.Item(“Title”)) Then If dr(“HomePhone”).Length > 40 Then AddError(“Home phone must be less than 40 characters long.”) End If End If If Not IsDBNull(dr.Item(“Title”)) Then If dr(“WorkPhone”).Length > 40 Then AddError(“Work phone must be less than 40 characters long.”) End If End If If Not IsDBNull(dr.Item(“Title”)) Then If dr(“Fax”).Length > 40 Then AddError(“Fax number must be less than 40 characters long.”) End If End If If Not IsDBNull(dr.Item(“Title”)) Then If dr(“EMail”).Length > 120 Then AddError(“Email address must be less than “ _ & “120 characters long.”) End If End If If Not IsDBNull(dr.Item(“Title”)) Then If dr(“WebPage”).Length > 120 Then AddError(“Web page address must be less than “ _ & “120 characters long.”) End If End If End Sub ‘ ‘ The base SaveRow method stores the DataRow into the ‘ DataSet, whether it’s a new or existing row. The ‘ rest of this routine handles specific validation ‘ for this type of data. ‘ Public Overloads Sub SaveRow(ByVal dr As DataRow) MyBase.SaveRow(dr) Validate() End Sub ‘ ‘ We separate the SaveRow method from the Save method ‘ to give us a chance to handle any validation. We have Listing 2.6 Person.vb Class (continued) Contact Manager Application 53 ‘ a verification here that the data is good before we ‘ continue, however. ‘ Public Sub Save() If Not Me.IsValid Then Throw New PersonException(Me.ValidationError) Exit Sub End If m_DA.Update(m_DS) End Sub ‘ ‘ Since we only have a single row in our DataSet, ‘ delete it and then update the database with the ‘ change. ‘ Public Sub Delete() If m_DS.Tables(0).Rows.Count > 0 Then m_DS.Tables(0).Rows(0).Delete() m_DA.Update(m_DS) End If End Sub End Class Listing 2.6 Person.vb Class (continued) Set Up the Class Structure The first part of the class sets up the inheritance between this class and the BaseSer- vices class. It also makes the SQL Server objects and the utility objects available by way of an Imports statement. We can always access our Database object as AtWorkUtili- ties.Database, but the Imports statement eliminates the need to type the namespace every time. In some cases, you may have to type the namespace to properly select the class. For example, if you have two assemblies, each of which has a class called Account, specifying the namespace will select the right one. In this case, we only have one Database class, so the Imports statement saves us from typing and makes the code a bit shorter. It doesn’t translate into more or less efficient code, since the compiler will figure out which object we need and use the correct one with or without the namespace prefix. Imports AtWorkUtilities Imports System.Data.SqlClient 54 Project 2 Public Class Person Inherits BaseServices The next step is to define any variables that need to be used at the class level. How- ever, for this particular class, all the important variables are already defined in the BaseServices class. Write the Class Constructors The Person class has three constructors. The first takes no parameters and is used to create a new object of this type. The SQL statement is used to format the structure of the tblPeople table so that the SqlDataAdapter object and the SqlCommandBuilder objects will work properly. The statement is written to never return any records—just the structure of the table. ‘ ‘ If no arguments are supplied, build a separate ‘ database connection for this object. ‘ Public Sub New() MyBase.New(New Database(), “SELECT * FROM tblPeople WHERE 1=0”) End Sub The second constructor accepts a Database object, but is also used for a new record. This handles cases in which the database connection has already been established. ‘ ‘ If database connection is supplied, store it ‘ in the private connection variable for this ‘ object. ‘ Public Sub New(ByVal db As Database) MyBase.New(db, “SELECT * FROM tblPeople WHERE 1=0”) End Sub The final constructor accepts both a database connection and the unique ID of the person to load. This case is used to edit the record. ‘ ‘ If both database and ID are supplied, retrieve ‘ data into the object from the database. ‘ Public Sub New(ByVal db As Database, _ ByVal ID As Integer) MyBase.New(db, “SELECT * FROM tblPeople WHERE pkPersonID = “ _ & ID.ToString) End Sub Contact Manager Application 55 Note that each constructor calls MyBase.New. The MyBase object refers to the base class from which this class derived; in this case, the base class is BaseServices. Create the Validation Routine The next step is to build the validation routine that validates the data in the object. Having the validation in the Person class keeps it consolidated in one place. The vali- dation routine verifies that all the fields are less than the maximum length defined by the database table. It also makes sure that either the person’s first and last name are supplied or that the company name is supplied. You could also write code verifying that the email address and Web page are properly formatted. The first part of the routine is the public method, called Validate. This checks the data currently in the object’s DataSet to verify that it meets the data validation rules that you have created in your object. Although we are only storing a single row, we use a loop here to go through all the rows anyway, thus supporting future expansion of the class to handle multiple additions at the same time. Building the loop here this way saves you from having to recode it later.Before validation, we check the row’s Row- State property. This property gives us an indication as to what has been done to the row. A row can be unmodified, added, modified, deleted, or detached. We don’t need to validate deleted rows, and we’re not using the DataSet feature to detach rows, so we only check the new or modified rows. Detached rows are DataRow objects that have either not been added to a DataSet or ones that were removed from a DataSet. Since the rows we are checking are always part of a DataSet, we don’t have to worry about detached rows here. ‘ ‘ Verify that all data validation rules have been ‘ met. Any errors get stored into the errors collection ‘ inherited from the BaseServices class. ‘ Public Sub Validate() Dim dr As DataRow ClearErrors() For Each dr In m_DS.Tables(0).Rows If dr.RowState = DataRowState.Added _ Or dr.RowState = DataRowState.Modified Then ValidateRow(dr) End If Next End Sub The private ValidateRow routine checks each row of data against the various rules we’ve already described. Note that we have to verify that a field is non-null before we attempt to check the data. If we don’t do that, we get errors. We use the IsDBNull func- tion to check for null in an object like this. Each field’s length is verified. We also check the first fields to verify that at least a company name, first, or last name is provided. 56 Project 2 [...]... Sub Validate() Dim dr As DataRow Listing 2. 16 The Note class 77 78 Project 2 ClearErrors() For Each dr In m_DS.Tables(0).Rows If dr.RowState = DataRowState.Added _ Or dr.RowState = DataRowState.Modified Then ValidateRow(dr) End If Next End Sub ‘ ‘ Checks an individual row for validation rule ‘ compliance Any errors are added to the errors ‘ collection ‘ Private Sub ValidateRow(ByVal dr As DataRow) If... {1}” + NewLine, _ sdrData(“LastName”), _ sdrData(“FirstName”)) sb.AppendFormat(“ {0}” + NewLine,_ sdrData(“Title”)) sb.AppendFormat(“ {0}” + NewLine, _ sdrData(“CompanyName”)) sb.AppendFormat(“ {0}” + NewLine, _ sdrData(“WorkPhone”)) sb.Append(“ ”) sb.AppendFormat(“Update”, _ sdrData(“pkPersonID”)) sb.Append(“  ”)... DataBinder.Eval(Container.DataItem, _ “Content”) %> Update   Delete ... valign=”top”> Update   . m_DS.Tables(0).Rows If dr.RowState = DataRowState.Added _ Or dr.RowState = DataRowState.Modified Then ValidateRow(dr) End If Next End Sub The private ValidateRow routine checks each row of data against the. collection; each Row is a DataRow object. We’ll be manipu- lating DataRow objects when we want to save the data. These DataRows are stored in the DataTable and DataSet objects. The DataSet object is fed. m_DS.Tables(0).Rows If dr.RowState = DataRowState.Added _ Or dr.RowState = DataRowState.Modified Then ValidateRow(dr) End If Next End Sub ‘ ‘ Checks an individual row for validation rule ‘ compliance.