I'm getting into Core Data and have started making "Classes" out of entities. Do I use these classes based off of entities as regular classes with methods etc?
Normally if I was using SQL directly I would have classes for each of my database objects (Tables) that store the working data and perform their functions.
Is this the same with Core Data - do I use the entity-based classes (subclasses of NSManagedObject).
So I might have these entities: Business -> Departments -> Employees
To comply with Core Data - do I make one class for each of these subclassing NSManagedObject and then add methods to it accordingly (like I would an NSObject class)?
Yes, you usually use the Core Data generated classes. You usually don't add methods to those classes, instead you should put them into a Category. This is because if you change an entity, you need to regenerate the class which will erase any methods that you added.
Yes(ish). They are your model classes. You aren't creating them 'out of' entities, they are the code representation of your entities.
You should have one class per entity, but you shouldn't create them yourself. You should get Xcode to create the classes. Or, better yet, use mogenerator.
Related
I have been working with C# using a repository design pattern with Entity Framework (EF) that allows me to interact with the database using a generic class for each table.
This repository has all the functions that I would need such as: Adding a new entity into the database, updating an existing entity, deleting an entity, saving the context and so on...
Take, for example, I have an entity called 'Person' in the database. I would create a new class called PersonRepository which had all the functions I would need to change/add a value to the database.
As a result, to interact with the database, you create an instance of the repository class. This then allows you to call the functions of this class which in turn interacts with the database. The idea of this pattern is that all your database calls for an entity are isolated into a single class, this improves testability and separation of concerns.
I am learning how to use Core Data in my Swift programs and it appears to be similar to that of EF in C#. I have created the entities in the .xcdatamodel file and created the associated Cocoa Touch class via the Editor > Create NSManageedObject subclasses option.
I used the 'Category/Extension' CodeGen option, so, I then created a new class called 'Exercise'. From what I have read, this class can contain additional logic such as overriding the prepareForDeletion method. Does this mean I can add the addEntity, updateEntity functions onto this method and then call them from other code files?
My questions are:
Can I implement the same repository pattern that I can use in C#?
I believe this would be on the generated class of my entity (see image below)
Where do I place all my database call functions? If I can use this repository pattern I will place them on there, however, if I cannot, do I place them in a separate code file? Should I place them on the generated entity file which is created for the purposes of adding additional logic?
If I can use the repository pattern, is there a way to get the context injected into this class, or, do I have to call a getContext method each time I want to change it? In C# we can use the services to inject the context into the class each time I want to make changes to the database - I am unsure if the same is possible in Swift.
If I understand correctly, in Swift the equivalent of your 'repository' class could be one of two things. It could be context of core data, which you'd run queries and saves to OR (more likely) you would create a new class or struct that obscured away core data from the business side. Assuming the later, your "dataManager" class would perform all interactions with core data. It could then either return NSmanagedobjects to the business side, or you could map/transform/convert to some other type.
Yes, Exercise is a object that subclasses nsmanagedobject, so it has all the core data features of a managed object, but you can add any custom functions your want.
Your data manager class would perform the queries and return the correct objects. For example data manger.getExercises() -> [Exercises], dataManager.save(_ exercise: Exercise), etc....
You'll need to consider thread safety in your pattern. One option is converting your nsmanagedobjects to struct in your datamanager and not returning nsmangedobjects. Structs are thread safe and using codable you can easily convert between exerciseManagedOjbect and exerciseStruct. Plus, with this dataManager class example, you could remove core data for another persistence option in the future with reduced impact to your app overall.
I have an macOS app being developed in Xcode (8.3.2) in SWIFT.
I have a CoreData model with a number of entities and an identifier (myidentifier).
I want to be able to identify the entities of the model programatically at runtime so that I can iterate through the entities and store data being sourced from a range of JSON files based on the data within the JSON file.
To date I have been creating entities and then writing a class for each entity to both save and fetch the data. It is working perfectly and as expected. However, if I continue like this I will end up with about 50 different entities and their associated class files (note that some while entities use a one to many relationship, the majority do not).
I would like to create a single class that will enumerate through the numerous entities of the model and store the relevant data (as well as its associated fetch routine).
I should also note that I am using NSManagedObject subclasses for each of the entities.
How do I obtain a NSManagedObjectModel reference to the model that I am using for the app? I can't seem to find the right mechanism to allow me to do this. Can I do this using the model identifier?
My thinking is that if I can then use entitiesByName I can make use of the resulting [String: NSEntityDescription] to then access my entities and enumerate as needed.
You could use mergedModel(from bundles: [Bundle]?) (see the documentation here, specfying Bundle.main to get the main bundle. Alternatively, your NSManagedObjectContext will have a reference to the persistentStoreCoordinator which will itself have a reference to the managedObjectModel.
Note that NSManagedObjectModel has an entities property so you can use:
for myEntity in myModel.entities { ... }
rather than using entitiesByName.
Its more of a best practices sort of question. Here it goes...
I have automatically generated some classes for my entities in core data , now I want to use them as model objects to convert those models in JSON and send it over to the server. So my question is whether it is ok to use these classes or should I create separate classes and use a data mapper class to map these core data and model classes...
Which is a better approach and why...?
Thanks for your inputs...
You can use your NSManagedObject subclasses and add methods to those classes as you would any other NSObject class. This is perfectly acceptable (and would be better practice than to create separate object classes and using data mappers).
Use mogen to avoid the problem mentioned by #svena. It will automatically manage generation of core data models to prevent overriding your own code. Also I would suggest trying RestKit for server interactions. At least you can borrow their object serialization code because it does exactly what you want.
I've tried to use Entity Framework 4 and POCO for my MVC 3 project. May be, I don't understand the main idea of this ORM, but the problem is following:
I added ADO .NET Entity Data Model and make model according to database.
I clicked Add Code Generation Item and added ADO .NET POCO Entity Generator.
It makes classes for every database table.
I want to add some methods to work with data (Add, Update, Delete, GetAll etc) to appropriate models.
For LINQTOSQL I added partial classes and placed them to Models. But now I can't do it because:
a) Models folder has classes with the same names, which was created by POCO.
b) If I place my partial class in the another folder, it will be another namespace - so, such classes won't be partial one.
c) If I place my code in POCO classes, it can be destroyed during update POCO.
How can I use it? Where sould I place my methods for data working?
Is the best way to make for POCO and EF the other project - http://blogs.msdn.com/b/adonet/archive/2010/01/25/walkthrough-poco-template-for-the-entity-framework.aspx?
First of all you don't have to write your CRUD inside POCO,
There are many places where you can do it like in edmx.cs file or write one more layer which is called as CRUD Services which handles the Database operations using context object.
Now coming to your questions,
Create separate Models folder and place the Model classes in there.
Your Model class may like this,
EmployeeDepartmentModel
{
prop EmpList List(Emp);
prop DeptList List(Dept);
//Emp and Dept are my POCOs
}
So now I have to fill both of these list(Your CRUD question),
For that, I will Create one method in Controller class(its better to write such logic in some another library, but for time being I suggest you to create in Controller),
FillTheModel()
{
EmployeeDepartmentModel.EmpList = EDMX.GetAllEmployees;
EmployeeDepartmentModel.DeptList = EDMX.GetAllDepartments;
}
Now you can bind this model with your view.
You can place the partial classes in another folder and modify the namespace.
I agree with allisewell, but if you really want to add parts to partial classes, give files another name,
e.g. MyPoco.Part2.cs or modify t4 template to name generated files
e.g. Poco.Generated.cs
I use standard ObjectContext and EntityObjects in my application. Let's say two of my tables are Projects & Services. Projects have Subproject (from Projects table with ParentID == ProjectID) and also Services. So I would have a hierarchy like Projects->Subprojects->Services. But I need to inherit Projects and Services from an abstract base class so I can use any of these entities as a new Task/Job entity in my application. Then, for example I can create a TreeList listing all Tasks (either a Project or Service). Is there anyway in EDMX designer I can create a new type (entity) which is the base calss for two or more concrete types?
It is possible with TPC inheritance but it will include a lot of complication to your design. For example:
you will have to move shared properties to the base class
you will probably have to maintain some mappings manually in EDMX (at least I had when I did the sample on screenshot)
you will have only single ObjectSet<Tasks> and you will have to use OfType to query only Projects or Services
you will have to use unique Id per Task = across both Project and Service tables (can be achieved by correctly configured identities in database)
It will look like:
Another option is using interface on your entity objects instead of parent class. You can define interface in your partial part of entity object and handle retrieving both Projects and Services by yourselves where your UI will expect only list of types implementing your interface.
http://blogs.microsoft.co.il/blogs/gilf/archive/2010/01/25/table-per-concrete-type-inheritance-in-entity-framework.aspx
Since it sounds like your data is coming from 2 separate tables, Projects and Services, no, I don't think you can achieve this in the designer (at least, not without hand-editing the generated edmx). If there were a common table to represent the base class, that could be done in the designer, but that doesn't sound like it fits your situation.
What you may be able to do is use an interface instead of an abstract base class, and use partial classes in your entity model to implement the interface for each of your entities. You can't directly inherit from your abstract base class in your entity model, because all of your entities already derive from EntityObject. If you have a lot of shared implementation that resides in your base class, it might be worthwhile to switch to POCO, where you can define your own inheritance hierarchy.