I'd like to place some custom methods directly into each NSManagedObject. Think, "calculated fields": these methods provide read-only calculated values based upon persistent values on the Entity - which is identical to this question.
I'm using the Xcode New File... Wizard to create NSManagedObject subclasses for each of my Entities. I'm trying to benefit from the system auto-creating the accessors for me. For example:
Core Data Entity: "Site"
#interface Site : NSManagedObject
As I continue to add new Attributes to my Entities, I'm replacing their corresponding NSManagedObjects by using the Wizard. When each file is replaced, my custom methods are lost.
Should I create my custom methods elsewhere so that I can continue to leverage the Wizard? Or, should I keep the methods on the NSManagedObject and add Accessors for new Attributes manually? Is there another approach?
Create a category on your NSManagedObject subclass:
In the "New File ..." dialog, choose "Objective-C category".
Create a category "CustomMethods" on "Site".
Xcode will create files Site+CustomMethods.h, declaring the #interface Site (CustomMethods), and Site+CustomMethods.m for the corresponding implementation.
Add your custom methods to the category.
These files will not be overwritten when you recreate Site.m and Site.h in Xcode.
All category methods can be used as if they had been declared in the class itself. The only thing you can not do in a category is add new instance variables.
Once I have used the wizard to create the initial managed objects, I generally change them manually.
Another way of doing this is to create subclasses of the wizard generated class files and use these.
When they are regenerated, all of your custom code is in the subclass, as opposed to the overwritten class file.
Related
This question already has answers here:
Automapper: Update property values without creating a new object
(4 answers)
Closed 4 years ago.
Is there any way to use Automapper 5.1.1 to update an existing object as opposed to creating a new one.
For example we have a Customer entity and a CustomerViewModel. We would like to update an existing Customer with the CustomerViewModel field values.
Would greatly appreciate your assistance.
It is not adviced to use Automapper to map a model to your Entity. Dependencies or Informations can be overwritten if it isn't used wisely.
But to use it as you want, you only need to create a map from your Model to your Entity and then call
Mapper.Map(myModel, myEntity);
The mapping to entity Problem
I guess you use a ORM like NHibernate or EF, then your Entites are Proxies, where references are proxies too and so on. Now lets imagine you have an ASP.NET MVC Project and you map your Entity to your ViewModel. You show your Model in your View as a form, but you only show the properties that you need in your view, not all that are set in your ViewModel. Then the user sends the Form back to you and your Controller gets the ViewModel back, but this time not all Properties are set, because your View only knew the ones that were shown. If you map your ViewModel back to your entity, all unitialized properties are in there default state and will overwrite the valid data f rom your entity.
Another Problem is, that AutoMapper uses Reflections to set the Properties. Normally the right to exist for an ORM is the possibility to easy implement an DomainLayer. The DomainLayer has some Validations, Calculation... on the Entity itself. If now the Properties set with Reflection it would ignore the Business logic and no Validation, Calculations.... would be executed.
So my advice is, Don't map to Entities ;)
I'm using Simperium and mogenerator in my project. I've added SPManagedObject entity to the model and set that as the parent class for other entities. For each entity, mogenerator automatically creates a _<entityname>.h and _<entityname>.m file that has several convenience accessors. I've modified the mogenerator build script so each of these subclasses SPManagedObject instead of NSManagedObject. The entity classes simply import the corresponding _<entityname>.h file.
My problem is I'm getting runtime errors when using any of the convenience accessors. For example, for an entity with attribute of type Integer32 called myInteger, the class file property is NSNumber. Mogenerator creates an accessor named myIntegerValue. The errors I'm getting are that myIntegerValue is an unrecognized selector for SPManagedObject. I can work around this obviously but it seems to be indicative of a bigger problem. Any ideas? Thanks!
This kind of problem is most often the result of failing to configure the class name in the Core Data model editor. You may have a class Foo and an entity Foo but they don't automatically go together (they're not required to have the same name). If you don't do this, you get instances of NSManagedObject instead of instances of your subclass. And of course, NSManagedObject doesn't have those methods.
Select the entity in the model editor and look in the model inspector on the right. Make sure that the class name is configured.
Is there a bulit-in way to obtain an entity name from the class object of an NSManagedObjectSubclass? I know that this can be readily determined from an instance of a subclass, but I want to ask the class itself. I can write a class function, but I would rather do this introspectively.
You can do it now by executing NSManagedObject.entity().name where NSManagedObject() is your subclass.
Check out mogenerator if you haven't already.
http://raptureinvenice.com/getting-started-with-mogenerator/
It adds a lot of missing features to core data. In particular it keeps you from having to regenerate your entity classes.
You could iterate thru the key values of the entities in the context:
[managedObjectContext registeredObjects];
I'm trying to build a custom HTML helper for MVC.NET that would allow me to render object entities (Model Objects) as HTML forms. So I decided to do it using custom attributes such as html input type, readonly flag, css classes, etc. Similar in a way to LINQ Mapping attributes that set database related bindings for Table and Column. So I did write a custom attribute class, applied it to the same entities that I store in the database, but when I retrieve an entity class from a database to display in a View, all of my custom attributes are gone. Is there a way to retain my custom attributes, AFTER they come back from a database?
I've got a SubSonic DAL - works great.
Two classes: TblReceipt and TblReceiptLineItems.
I can create a parallel class of TblReceipt, but seems like a waste, so here's what I need to do:
Have a Class TblReceipt with one additional member, "ReceiptLineItems" - which is simply an ArrayList. This array list will be populated with TblReceiptLineItems types.
So for each Receipt, there are 1..* ReceiptLineItems stored in the array, then the whole thing is serialized.
How can I accomplish this with my existing SubSonic DAL?
A quick code sample would be useful too.
Thank you.
Use a partial class. All classes in Subsonic are defined as partial. What you do is (in a separate file than the one that is generated by Subsonic), you create another part of the partial class with the additional property.
Option 2 here:
http://jamesewelch.wordpress.com/2008/09/24/how-to-use-custom-audit-fields-with-subsonic/