fetch请求问题

发布于 2024-11-03 17:19:05 字数 558 浏览 0 评论 0原文

在核心数据中，我使用 fetchRequest 和谓词进行搜索，如下所示

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
             entityForName:@"Study"
    inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:
                                @"( StudyID == %@ )",self.StudyID]];

NSArray * StudyList  = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];

如何检查是否有返回值

原文

in core data , I search using fetchRequest and predicate like the following

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
             entityForName:@"Study"
    inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:
                                @"( StudyID == %@ )",self.StudyID]];

NSArray * StudyList  = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];

how to check if there a return values or not

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究竟谁懂我的在乎 2024-11-10 17:19:05

做一些类似的事情：

if(!StudyList){
    //handle fetch request error here
} else {
    //success! 
    if([StudyList count] > 0){ //if array not empty
        //do stuff with StudyList contents here
        NSLog(@"StudyList contents: %@", StudyList);
    }
}

希望有帮助。

Do something like:

if(!StudyList){
    //handle fetch request error here
} else {
    //success! 
    if([StudyList count] > 0){ //if array not empty
        //do stuff with StudyList contents here
        NSLog(@"StudyList contents: %@", StudyList);
    }
}

Hope that helps.

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再可℃爱ぅ一点好了 2024-11-10 17:19:05

您可以像这样检查 StudyList 数组的大小：

if ([StudyList count]>0){
    //... found at least one Study object
}else{
    //... didn't find anything
}

顺便说一句，您应该遵循命名约定。像 StudyList 这样的变量应该以小写字母开头，即 studyList。按照惯例，以大写字母开头的名称表示某种常量，例如类、实体、常量等。

You check the size of the StudyList array like so:

if ([StudyList count]>0){
    //... found at least one Study object
}else{
    //... didn't find anything
}

As an aside, you should follow the naming conventions. A variable like StudyList should be written starting with lower case i.e. studyList. By convention, names that start with capital letters indicate some sort of constant e.g. classes, entities, constants etc.

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