I know that if you change the Core Data model and you have run the app before on the old model that you will get Persistent Store error. How would you handle changes to the Core Data model so you do not get this error? Is there a way to upgrade an old model so that the already saved data is not lost?
Core Data comes with a built-in mechanism to handle changes to your model.
Take a look at the Core Data Model Versioning and Data Migration Programming Guide for details.
If 10.6 is your baseline OS then you can use lightweight migration, specifically NSInferMappingModelAutomaticallyOption.
The article I wrote is similar and useful if 10.6 is not your baseline OS.
Related
I'd like to train a model using Spark ML Lib but then be able to export the model in a platform-agnostic format. Essentially I want to decouple how models are created and consumed.
My reason for wanting this decoupling is so that I can deploy a model in other projects. E.g.:
Use the model to perform predictions in a separate standalone program which doesn't depend on Spark for the evaluation.
Use the model with existing projects such as OpenScoring and provide APIs which can make use of the model.
Load an existing model back into Spark for high throughput prediction.
Has anyone done something like this with Spark ML Lib?
Version of Spark 1.4 now has support for this. See latest documentation. Not all models are available (see to be supported (see the JIRA issue SPARK-4587).
HTHs
We have an app in ASP.NET MVC 3 that, due to legacy and porting reasons, is written entirely using traditional ADO.NET for the data layer.
I am now tasked with adding some reporting to this website, and the reports can result in some extremely complicated queries.
Are there any pitfalls in using the EF Power Tools to reverse-engineer a code first model and using it side-by-side with our current ADO.NET model? Doing so would allow me to use LINQ for querying the data I need, greatly speeding up the time required to write each report. I would need to shut off data context initialization, as we have our current model do that, but are there any glaring risks or problems associated with trying to do this?
If it's of any relevance (I know EF 5 has a ton of new features), we are using .NET 4 and will begin moving to .NET 4.5 as soon as it launches.
I think this is a very sensible thing to do. You could also use a database-first model, which you can refresh whenever the database changes and which does not try to initialize a database.
Since you will use the context read-only you can optimize the query process by setting the MergeOption property of ObjectQuerys to MergeOption.NoTracking. This reduces overhead because the context will not track changes of the generated objects.
A problem might be that there is more maintenance if the database changes, but I think the absence of walls of boiler-plate query code for reporting on the old data layer far outweighs that.
One day :) you may even decide to use the EF model to display data that users want to filter in the UI and use the old data layer for CUD commands. (a bit like CQRS).
I want to make a program for a restaurant, to hold foods and store customer recipe. What is the best way to store data? (core data - sqlite - ...)
You will find a conversation about core data vs. sqlite here. But, with iOS 5.0 you get the added benefit of being able to use iCloud file-sync for free if you're using Core Data. If you're using SQLite directly it'll have to be a lot of manual tinkering and implementation to get it to sync across iCloud.
I've found no clear answer so far, but maybe I've searched the wrong way.
My Question is, can Core Data to be used as a Persitence Storage for a Server Project? Where are Core Data's Limits, how much Data can be handled with Core Data and SQLite? SQLite should handle a lot of Data very well according to their website. I know of a properitary Java Persitence Manager with an Oracle DB as Storage that handles Millions of Entries and 3000 Clients without Problems. For my own Project I wonder if I can use Core Data on the Server Side for User Mangament and intern microblogging, texting with up to 5000 clients. Will it handle such big amounts of Data or do I have to manage something like that myself? Does anyone happend to have experience with huge amounts if Data and Core Data?
Thank you
twickl
I wouldn't advise using Core Data for a server side project. Core Data was designed to handle the data of individual, object-oriented applications therefore it lacks many of the common features of dedicated server software such as easily handling multiple simultaneous accesses.
Really, the only circumstance where I would advise using it is when the server side logic is very complex and the number of users small. For example, if you wanted to write an in house web app and have almost all the logic on the server, then Core Data might serve well.
Apple used to have WebObjects which was a package to manage servers using an object-oriented DB much like Core Data. (Core Data was inspired by a component of WebObjects called Enterprise Objects.) However, IIRC Apple no longer supports WebObjects for external use.
Your better off using one of the many dedicated server packages out there than trying to roll your own.
I have no experience using Core Data in the manner you describe, but my understanding of the architecture leads me to believe that it could be used, depending on how you plan to query and manipulate the data.
Core Data is very good at maintaining an object graph and using faults to bring parts into memory as needed. In that manner, it could be good on a server for reducing memory requirements even with a large data set.
Core Data is not very good at manipulating collections of objects without loading them into memory, making a change, and writing them back out to disk. Brent Simmons wrote a blog post about this, where he decide to stop using Core Data for some of his RSS reader's model objects because an operation like "mark all as read" didn't scale. While you would like to be able to say something like UPDATE articles SET status = 'read', Core Data must load each article, set its status property, then write it back to disk.
This isn't because Apple engineers are stupid, but because the query layer can't make assumptions about the storage layer (you could be using XML instead of SQLite) and it also must take into account cascading changes and the fact that some article objects may already be loaded into memory and will need to be updated there.
Note that you can also write your own storage providers for Core Data, see Aaron Hillegass's BNRPersistence project. So if Core Data was "mostly good" you might be able to improve on it for your application.
So, a possible answer to your question is that Core Data may be appropriate to your application, as long as you do not need to rely on batch updates to large number of objects. In general, no algorithm or data structure is appropriate for every scenario. Engineering is about wisely choosing between trade-offs. You won't find anything that works well for many clients in every case. It always matters what you are doing.
I'm trying to design a simple Cocoa application and I would like to have a clear and easy to understand software architecture. Of course, I'm using a basic MVC design and my question concerns the Model layer. For my application, the Model represents data fetched on the Internet with a XML-RPC API. I'm planning to use Core Data to represent a locally fetched version. How should the data be loaded initially? I'm reading the Cocoa Design Pattern book, and they talk about a Model-Controller that is centric to the Model. How would that be done?
Thanks!
Your question is sort of open ended so I will give you my take as someone who has gone through the process of redesigning a poorly built application.
The idea for your model is quite simple:
Create a Data Model (this involves creating your Entities, their properties and relationships).
Put code in place to create a Managed Object Context using the Data Model created in step 1.
Fetch your data from the Internet and create NSManagedObjects based on your Data Model
After step three you will have a Core Data representation of your model in memory, which you can use to drive your user interfaces, or save to a persistent store (to file).
The Core Data documentation, covers each one of the above steps in further detail.