DataPortal_Create in Visual Basic .NET

Creator PDF-417 2d barcode in Visual Basic .NET DataPortal_Create

The DataPortal_Create() method is called by the data portal when it is asked to create a new Project object. In some cases, this method will load the new object with default values from the database, and in simpler cases, it may load hard-coded defaults or set no defaults at all. The Project object has no need for loading default values, so the DataPortal_Create() method simply loads some default, hard-coded values rather than talking to the database: <RunLocal()> _ Private Overloads Sub DataPortal_Create(ByVal criteria As Criteria) mId = Guid.NewGuid Started = CStr(Today) ValidationRules.CheckRules() End Sub The method is decorated with the <RunLocal()> attribute because it doesn t do any data access, but rather sets hard-coded or calculated default values. If the method did load default values from the database, then the <RunLocal()> attribute would not be applied, causing the data portal to run the code on the application server. With the <RunLocal()> attribute on the method, the data portal short-circuits its processing and runs this method locally.

s In a more complex object, in which default values come from the database, this method would contain Tip ADO.NET code that retrieves those values and uses them to initialize the object s fields. In that case, the <RunLocal()> attribute would not be used.

Notice how the code directly alters the instance fields of the object. For instance, the mId field is set to a new Guid value. Since the Id property is read-only, this is the only way to load the Id property with a new value. While the Started property is read-write and could be set through the property, it is more efficient and consistent to directly set the mStarted field. Since not all properties can be set, it is best to be consistent and always set fields directly. Additionally, the ValidationRules.CheckRules() call will apply all the validation rules in the entire object. Setting a property causes the validation rules for that property to be checked, so setting property values would cause validation rules to be run twice, which is wasteful. Setting the fields and then calling CheckRules() means validation rules are run only once. Of course, the default values set in a new object might not conform to the object s validation rules. In fact, the Name property starts out as an empty String value, which means it is invalid, since that is a required property. Remember that this was specified in the AddBusinessRules() method by associating this property with the StringRequired rule method. To ensure that all validation rules are run against the newly created object s data, ValidationRules.CheckRules() is called. Calling this method with no parameters causes it to run all the validation rules associated with all properties of the object, as defined in the object s AddBusinessRules() method. The end result is that the new object has been loaded with default values, and those values have been validated. The new object is then returned by the data portal to the factory method (NewProject() in this case), which typically returns it to the UI code.

More interesting and complex is the DataPortal_Fetch() method, which is called by the data portal to tell the object that it should load its data from the database (or other data source). The method accepts a Criteria object as a parameter, which contains the criteria data needed to identify the data to load: Private Overloads Sub DataPortal_Fetch(ByVal criteria As Criteria) Using cn As New SqlConnection(Database.PTrackerConnection) cn.Open() Using cm As SqlCommand = cn.CreateCommand cm.CommandType = CommandType.StoredProcedure cm.CommandText = "getProject" cm.Parameters.AddWithValue("@id", criteria.Id) Using dr As New SafeDataReader(cm.ExecuteReader) dr.Read() With dr mId = .GetGuid("Id") mName = .GetString("Name") mStarted = .GetSmartDate("Started", mStarted.EmptyIsMin) mEnded = .GetSmartDate("Ended", mEnded.EmptyIsMin) mDescription = .GetString("Description") .GetBytes("LastChanged", 0, mTimestamp, 0, 8) ' load child objects .NextResult() mResources = ProjectResources.GetProjectResources(dr) End With End Using End Using End Using End Sub