哪个更好:全局字符串或单例? [英] What is better: Global string or singleton?

问题描述

对于我的全新ORM( chibi-ORM )，我面临一个设计决策.

For my brand new ORM (chibi-ORM) I face a design decision.

我正在建立关系的API，例如:

I'm building the API for relationships, like:

@interface SamplePerson : DbObject {
    NSString *name;
        DbObjectRelation *cities;
}

现在，对于 DbObjectRelation ，我有这个模型:

Now, for DbObjectRelation I have this mockup:

@interface DbObjectRelation : NSObject {
    NSMutableArray *childRows;
    DbObject *parent;
    BOOL isLoaded;
}

-(void) load;

-(void) addObject:(DbObject *) childRow;
-(void) removeObject:(DbObject *) childRow;

- (id)initWitParent:(DbObject *)parentObject;

因此，我需要一种内部加载方式来知道哪个数据库用于加载记录.

So, I need a way inside load of know which database use for load the records.

我认为数据库连接中包含以下内容:

I think in have in my DB connection something like:

static NSString *currentDbNameSingleton = nil;

+(NSString *)currentDbName {
    @synchronize( self ) {
        if ( currentDbNameSingleton == nil ) {
            currentDbNameSingleton = [[NSString alloc]
        }
    }
    return sharedInst;  
}

+(void) setCurrentDbName(NSString *)name {
    @synchronize( self ) {
      currentDbNameSingleton = [name copy];
    }
}

但是想知道是否最好将DB类构建为单例.这是用于iPhone项目...

But wonder if is better build the DB class as a singleton. This is for iPhone projects...

推荐答案

像当前正在使用的那样，在静态变量周围使用一组类访问器/变量是很合理的.如果不打算更改数据库名称，另一种非常常见的解决方案是将其与单独的文件(例如Constants.h)以及其他常量字符串(例如字典和用户默认键)一起放置在一个文件中.

Using a set of class accessors/mutators around a static variable like you're currently doing is pretty reasonable. Another pretty common solution if you're not going to change the database name would be to put it in a separate file, say Constants.h, along with other constant strings like dictionary and user defaults keys.

如果您有与数据库相关的其他代码可以重构到一个地方，那么为数据库内容构建单例类是一个很好的方法.我不会创建仅用于容纳字符串的类.

If you have additional code related to your database that you can refactor into a single place, then that's a pretty good point to built a singleton class for your database stuff. I wouldn't create a class just to hold a string though.

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