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Figure 17.15 The UI using the new EmployeePresentationModel class. Note how you have fields from the contact object now available to the UI.
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When you run the application, you ll see something like figure 17.15. The new UI has fewer fields and looks a lot better than what you had before. You have a lot fewer fields in the UI now. Some, like Birth Date, which have had the Display attribute applied, have better labels and column headers. You could set the display name for the remaining ones, and the display order, as well using the same attribute. For space reasons, I didn t include the attributes in the listings here. The presentation model approach certainly works in this situation. It s not meant just for flattening objects, although you can use it for that. It also shines in situations where you need to do joins in LINQ and combine the results into a single logical object. Retrieval is fine for a demo, but the real test comes when you need to use this information in an update operation.
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17.5.3 Supporting update operations
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To perform an update using the presentation model approach, you ll need to map from the presentation model class to the back to the entities used in the backing store. Essentially, you re doing the reverse of what you did in the query operation.
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Loose coupling: using presentation models
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Listing 17.6 shows how to map from the presentation model back to the database entities.
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Listing 17.6 The UpdateEmployee method
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private void MapEmployee(Employee emp, EmployeePresentationModel employeePM) { emp.BirthDate = employeePM.BirthDate; emp.CurrentFlag = employeePM.CurrentFlag; emp.Contact.EmailAddress = employeePM.EmailAddress; emp.Contact.EmailPromotion = employeePM.EmailPromotion; emp.Contact.FirstName = employeePM.FirstName; emp.Contact.LastName = employeePM.LastName; emp.Contact.NameStyle = employeePM.NameStyle; emp.Contact.Phone = employeePM.Phone; emp.NationalIDNumber = employeePM.NationalIDNumber; emp.SalariedFlag = employeePM.SalariedFlag; emp.SickLeaveHours = (short)employeePM.SickLeaveHours; emp.Title = employeePM.Title; emp.HireDate = employeePM.HireDate; emp.Gender = employeePM.Gender; emp.VacationHours = (short)employeePM.VacationHours; emp.MaritalStatus = employeePM.MaritalStatus; emp.LoginID = employeePM.LoginID; Get current } persisted entity [Update] public void UpdateEmployee(EmployeePresentationModel employeePM) { Employee emp = _context.Employees. Where(e => e.EmployeeID == employeePM.EmployeeID) .FirstOrDefault(); MapEmployee(emp, employeePM);
EmployeePresentationModel original = this.ChangeSet .GetOriginal<EmployeePresentationModel>(employeePM); if (original.CurrentFlag != employeePM.CurrentFlag || original.EmailAddress != employeePM.EmailAddress || original.EmailPromotion != employeePM.EmailPromotion || original.FirstName != employeePM.FirstName || original.LastName != employeePM.LastName || original.NameStyle != employeePM.NameStyle || original.Phone != employeePM.Phone) { emp.Contact.ModifiedDate = DateTime.Now; } Save to _context.SaveChanges();
database
You re definitely in manual-plumbing land at this point. Of course, if you want to have separation between two layers, you ll have some mapping. Here, the mapping is in a
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WCF RIA Services
reusable function so the Insert method can use it. Note how you check the original employee to see if there were any changes before setting the modified date for the Contact object. You ll want to do the same for the Employee object; I left that out for space considerations. The code you write in this function will be pretty dependent on your choice of data access layer. The code here works well with the Entity Framework objects. The next type of operation you ll need to support is the insertion of new objects. This one can get tricky due to the creation of dependent entities and the generation of keys.
17.5.4 Supporting insert operations
Update operations are easy, because you often don t have to worry much about entity relationships or foreign keys. Insert operations usually have a few extra steps to perform in addition to the mapping. Listing 17.7 shows the InsertEmployee function. This function makes use of the MapEmployee function from the previous listing.
Listing 17.7 The InsertEmployee function
[Insert] public void InsertEmployee(EmployeePresentationModel employeePM) { Contact contact = _context.Contacts.CreateObject(); Employee emp = _context.Employees.CreateObject(); emp.Contact = contact; MapEmployee(emp, employeePM); contact.ModifiedDate = DateTime.Now; contact.rowguid = Guid.NewGuid(); contact.PasswordHash = "Adventure"; contact.PasswordSalt = "xyzzy"; emp.ModifiedDate = DateTime.Now; emp.rowguid = Guid.NewGuid(); _context.Contacts.AddObject(contact); _context.Employees.AddObject(emp); _context.SaveChanges(); }
This function creates the Contact and Employee data entities and sets the contact to be the contact for the Employee. It then calls the MapEmployee function from the previous listing to map the presentation model properties to the data entity properties. The next step is to set a few fields; the password-related fields here are dummies, but the modified date fields are correct. The last step before saving changes is to add the Contact and Employee to the entity sets. Finally, with a call to SaveChanges, the information all goes in the database.
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