CoreData在iPhone上支持IN谓词吗？ [英] Does CoreData on iPhone support IN predicates?

问题描述

我试图根据用户定义的类型列表获取一定类型的记录...

I'm trying to fetch a bunch of records of a certain type, based on a list of types defined by the user…

[fetchRequest setEntity:[NSEntityDescription entityForName:@"myRecord" inManagedObjectContext:self.managedObjectContext]];  
NSSet   *shipTypes = [NSSet setWithObjects:[NSNumber numberWithInt:70],
                    [NSNumber numberWithInt:71],
                    [NSNumber numberWithInt:72],
                    [NSNumber numberWithInt:73],
                    [NSNumber numberWithInt:74],
                     nil];
NSPredicate *aPredicate = [NSPredicate predicateWithFormat:@"type in %@", shipTypes];
[fetchRequest setPredicate:aPredicate];
theRecords = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];

...运行时，executeFetchRequest消息引发异常...

…when run, the executeFetchRequest message throws an exception…

 *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'unimplemented SQL generation for predicate : (type IN {71, 73, 70, 72, 74})'

我做错了什么，还是真的不支持？

Have I done something wrong, or is this really not supported?

推荐答案

我相信Alex是正确的，你必须使用NSArray，虽然显然它会更好，如果NSSet在这里被接受，因为顺序不是这很重要（虽然它可以影响到SQL可以多快运行）。

I believe Alex is right that you have to use an NSArray, although obviously it'd be nicer if NSSet were accepted here, since order isn't that important (although it could conceivably affect how quickly the SQL can run).

另外，我从来没有在任何代码中使用+ predicateWithFormat：因为它不能做编译时的完整性或类型检查。

As a side note, I never use the +predicateWithFormat: call in any code, ever, because it can't do compile-time sanity or type-checking. I highly advise using the individual classes.

在这种情况下，我会：

fetchRequest.entity = [NSEntityDescription entityForName:@"myRecord" inManagedObjectContext:self.managedObjectContext]];

NSArray *shipTypes = [NSArray arrayWithObjects:[NSNumber numberWithInt:70],
                                        [NSNumber numberWithInt:71],
                                        [NSNumber numberWithInt:72],
                                        [NSNumber numberWithInt:73],
                                        [NSNumber numberWithInt:74],
                                         nil];
fetchRequest.predicate = [NSComparisonPredicate predicateWithLeftExpression:[NSExpression expressionForKeyPath:@"type"] rightExpression:[NSExpression expressionForConstantValue:shipTypes] modifier:NSDirectPredicateModifier type:NSInPredicateOperatorType options:0];

theRecords = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];

不是这会在编译时捕获这个特定的错误， NSExpression级别，从而使它更清楚什么错误。

Not that this would have caught this particular error at compile time, but it WOULD have potentially caught it at the NSExpression level, thus making it much clearer what went wrong.

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