objective-c – 动态创建具有不同数量的属性和值的谓词

最干净的解决方案是使用NSExpression,NSComparisonPredicate和NSCompoundPredicate在代码中构建谓词.这将允许您为每个搜索自定义谓词.

像这样的东西：

-(NSPredicate *) predicateWithStudyID:(NSString *) aStudyID studyName:(NSString *) aStudyName date:(NSDate *) aDate{
  NSPredicate *p;
  NSMutableArray *preds=[[NSMutableArray alloc] initWithCapacity:1];
  if (aDate != nil) {
    NSExpression *dateKeyEx=[NSExpression expressionForKeyPath:@"studyDate"];
    NSExpression *aDateEx=[NSExpression expressionForConstantValue:aDate];
    NSPredicate *datePred=[NSComparisonPredicate predicateWithLeftExpression:dateKeyEx
                                                             rightExpression:aDateEx 
                                                                    modifier:NSDirectPredicateModifier
                                                                        type:NSEqualToPredicateOperatorType
                                                                     options:0];
    [preds addObject:datePred];
  }
  if (![aStudyID isEqualToString:@""]) {
    NSExpression *studyIDKeyEx=[NSExpression expressionForKeyPath:@"studyID"];
    NSExpression *aStudyIDEx=[NSExpression expressionForConstantValue:aStudyID];
    NSPredicate *studyIDPred=[NSComparisonPredicate predicateWithLeftExpression:studyIDKeyEx
                                                                rightExpression:aStudyIDEx 
                                                                       modifier:NSDirectPredicateModifier
                                                                           type:NSLikePredicateOperatorType
                                                                        options:NSCaseInsensitivePredicateOption];
    [preds addObject:studyIDPred];
  }
  if (![aStudyName isEqualToString:@""]) {
    NSExpression *studyNameKeyEx=[NSExpression expressionForKeyPath:@"studyName"];
    NSExpression *aStudyNameEx=[NSExpression expressionForConstantValue:aStudyName];
    NSPredicate *studyNamePred=[NSComparisonPredicate predicateWithLeftExpression:studyNameKeyEx
                                                                rightExpression:aStudyNameEx 
                                                                       modifier:NSDirectPredicateModifier
                                                                           type:NSLikePredicateOperatorType
                                                                        options:NSCaseInsensitivePredicateOption];
    [preds addObject:studyNamePred];
  }
  p=[NSCompoundPredicate andPredicateWithSubpredicates:preds];  
  [preds release];
  return p;
}

然后你会像这样使用它：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {  
  NSDate *firstDate=[NSDate date];
  NSDate *secondDate=[firstDate dateByAddingTimeInterval:60*60*24];
  NSDate *thirdDate=[secondDate dateByAddingTimeInterval:60*60*24];

  // I use an array of dictionaries for convenience but it works
  //   for managed objects just as well. 
  NSDictionary *d1=[NSDictionary dictionaryWithObjectsAndKeys:
                   @"abc123",@"studyID",@"firstStudy",@"studyName",firstDate,@"studyDate",nil];
  NSDictionary *d2=[NSDictionary dictionaryWithObjectsAndKeys:
                    @"abc456",@"secondStudy",secondDate,nil];
  NSDictionary *d3=[NSDictionary dictionaryWithObjectsAndKeys:
                    @"abc789",@"thirdStudy",thirdDate,nil];
  NSArray *a=[NSArray arrayWithObjects:d1,d2,d3,nil];
  NSPredicate *p=[self predicateWithStudyID:@"" studyName:@"thirdStudy" date:thirdDate];
  NSLog(@"p = %@",p);  
  NSArray *filtered=[a filteredArrayUsingPredicate:p];
  NSLog(@"%@",filtered);
  return YES;                           
}

见Predicate Programming Guide: Creating Predicate Directly in Code

更新：

下面的@DaveDelong指出,在上面的第一个代码块中,我创建的subpredicates过于复杂.在这种情况下(除执行速度之外)不需要从表达式生成子预测.而只是像往常一样构建子预测,然后像这样复合它们：

-(NSPredicate *) predicateWithStudyID:(NSString *) aStudyID studyName:(NSString *) aStudyName date:(NSDate *) aDate{
  NSPredicate *p;
  NSMutableArray *preds=[[NSMutableArray alloc] initWithCapacity:1];
  if (aDate != nil) {
    NSPredicate *datePred=[NSPredicate predicateWithFormat:@"studyDate==%@",aDate];    
    [preds addObject:datePred];
  }
  if (![aStudyID isEqualToString:@""]) {
    NSPredicate *studyIDPred=[NSPredicate predicateWithFormat:@"studyID Like %@",aStudyID]; 
    [preds addObject:studyIDPred];
  }
  if (![aStudyName isEqualToString:@""]) {
    NSPredicate *studyNamePred=[NSPredicate predicateWithFormat:@"studyName Like %@",aStudyName]; 
    [preds addObject:studyNamePred];
  }
  p=[NSCompoundPredicate andPredicateWithSubpredicates:preds];  
  [preds release];
  return p;
}