在iPhone Core Data或SQLite中存储长期数据的最佳方法是什么？

Question

I am working on iPhone app targeting 3.1.3 and later SDK. I want to know the best way to store user's long term data on iphone without losing performance, consistency and security.

I know, that I can use Core Data, PList and SQL-Lite for storing user specific data in custom formats.But, want to know which one is good to use without compromising app performance and scalability in near future.

Answer 1

It depends. The term "user data" covers a wide scale in size, complexity and usage each of which have different optimal storage strategies.

(1) If size and complexity are low and the usage is primarily controlling the app itself, store the data in the user defaults using NSUserDefaults.

(2) If the size is small and the complexity can be managed by arrays, dictionaries etc then store in a plist. Size counts because all the data stored in a plist is loaded into memory in one chunk.

(3) If the size is very large but the complexity is low eg a large number of template records such as an index card system, then use direct SQL. SQL is faster for finding and saving simple and repetitive information in a very large DB.

(4) If the complexity is very high, use Core Data regardless of size. Core Data is specifically designed to manage complex information. If the size is small, use an xml store. If it is large, use a SQL store.

As I gained familiarity with Core Data, I find myself using it for almost everything except user defaults. It has a steep learning curve but once you master it, you have a powerful and easy to use tool for managing application data. I probably use it in situations where it is not optimal just because it speeds development time.

Answer 2

I have to disagree on TechZen's list. Number 3 is only a right answer if you are dealing with a legacy SQLite database. There is never a reason to choose raw sqlite over Core Data. Core Data will perform better in nearly every situation and will reduce the amount of code you have to write by a significant amount.

In addition, I would caution against using plists. They are expensive to read and write and a Core Data database will outperform them in nearly every situation.

As for using Core Data, you should always use a SQLite back-end (XML is not available on iOS) except in the most extreme circumstances.

In short, if you are saving a single value, store it in NSUserDefaults .

Otherwise use Core Data.

Update

There is one SINGLE thing that cannot be done with Core Data more performant than raw SQLite currently. That is the ability to update a single column's values across tens of thousands of rows. That is because to modify a row, Core Data loads that row into memory and then writes it back out again.

For every other situation you are going to gain better performance with Core Data than you are writing your own accessors, objects and dealing with the memory and lifecycles thereof.

Core Data will outperform any data accessors that you are going to write yourself and it is going to handle writing to and reading from the underlying file in a better manner than you are. Why re-invent the wheel?