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The retrieval of a child object can be done in two different ways. You can use the data portal s support for loading child objects, or you can have your parent objects call methods on the child objects to create and load those objects however you choose. The advantage to using the data portal to load the child objects is that it enables a simple and consistent approach for loading data into any object. However, there is some overhead to using the data portal in this manner, so it may not be appropriate in very performance-intensive scenarios. The advantage to writing the code yourself is that you can design an optimized approach for your particular objects, and that may be very fast. However, you lose the benefits of standardization and simplicity provided by the data portal. Also, you must remember to have each child object manually call MarkAsChild() as it is created, typically in its constructor.
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CH A PT ER 4 C SLA .NET O BJECT S TER EOT YPES
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Note I believe it is important, when possible, to offer choices between performance and maintainability/ simplicity. This allows individual application designers to make choices based on the needs of their specific organization and application. This type of choice, enabling you to trade off one cost/benefit for another, can be found in many places throughout CSLA .NET.
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Either way, the steps are basically the same. As stated earlier, the root object s DataPortal_Fetch() method or factory fetch method is responsible for loading not only the root object s data but also the data for all child objects. It then either calls the data portal or methods on the child objects themselves, passing the preloaded data as parameters so the child objects can load their fields with data. The sequence of events goes like this: 1. The root object s DataPortal_Fetch() creates the child collection using a factory method on the collection class (scoped as Friend) and it passes an object containing the child data as a parameter. 2. The child collection s constructor loops through the list of child data provided by the parent, performing the following steps for each record: a. The child collection creates a child object by calling a factory method on the child class, passing the data for that particular child as a parameter. b. The collection object adds the child object to its collection. 3. At the end of the list of child data, the child collection and all child objects are fully populated. Figure 4-11 is a sequence diagram that illustrates how this works using the data portal. Note that this diagram occurs during the process of loading the root object s data. This means that this diagram is really an expansion of Figure 4-8, the sequence diagram for retrieving a root object.
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Figure 4-11. Loading child objects with data
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CHAPTER 4 CSLA . NET OBJECT STEREOTYPES
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For read-only objects, retrieval is the only data-access concept required. Editable business objects and editable collections (those deriving from BusinessBase and BusinessListBase) support update, insert, and delete operations as well.
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Adding and Editing Root Objects
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After an object is created or retrieved, the user will work with the object, changing its values by interacting with the user interface. At some point, the user may click the OK or Save button, thereby triggering the process of updating the object into the database. The sequence of events at that point is as follows: 1. The UI calls the Save() or BeginSave() method on the business object. 2. The Save() and BeginSave() methods call DataPortal.Update() to start the data portal process. 3. The data portal does one of the following: If no ObjectFactory attribute is specified, the data portal calls a DataPortal.Update(), DataPortal_Insert(), or DataPortal_DeleteSelf() method on the business object as appropriate; those methods contain the data access code needed to update, insert, or delete the data in the database. If an ObjectFactory attribute is specified, the data portal creates an instance of the specified factory class and calls the specified update method on the factory object. That update method is responsible for inserting, updating, or deleting the business object s data and returning an updated object as a result. 4. During the update process, the business object s data may change. 5. The updated business object is returned as a result of the Save() method. If no ObjectFactory attribute is specified on the business class, from the business object s perspective, two methods are called: Save() One of DataPortal_Update(), DataPortal_Insert(), or DataPortal_DeleteSelf() Figure 4-12 illustrates this process. If an ObjectFactory attribute is specified on the business class, the business developer is responsible for creating two classes: the object factory class and the business class. Figure 4-13 illustrates that the object factory class must implement an update method that manages all insert, update, and delete operations for the business object type. The Save() and BeginSave() methods are implemented in BusinessBase and BusinessListBase and typically require no change or customization. The framework s save methods include checks to ensure that objects can be saved only if the object is valid, has been changed, and isn t currently being edited and the user is authorized to do the update. This helps to optimize data access by preventing the update of an object that clearly can t be updated.
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