ios - CoreData 在 NSFetchRequest 找到新对象之前需要一些时间

Question

我的应用程序中有一个表单，允许用户输入文本并将其保存到 UIManagedDocument 中的 CoreData。

当应用程序正在运行时，我使用 NSManagedObjectContext 作为唯一的上下文，用于从该文档中插入和获取对象。

我遇到的问题是 - 在保存之前我会检查重复项，如果我在等待 10 秒后进行后续插入，context 不会确认已插入([匹配计数] 返回 0) 个对象，并允许重复。

另一方面，如果我等待它 - 结果如预期([matches count] 返回任何数字为真)。

完整代码

@implementation Student (Create)

+ (Student *)withInfo:(NSDictionary *)infoDictionary inManagedContext:(NSManagedObjectContext *)context
{
    Student *student = nil;

    // Check for duplicates
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Student"];
    request.predicate = [NSPredicate predicateWithFormat:@"studentID == %@", (NSString *)infoDictionary[@"studentID"]];
    [request includesPendingChanges];

    NSError *error = nil;
    NSArray *matches = [context executeFetchRequest:request error:&error];

    if (!matches || ([matches count] > 1)) {
        // handle error
        NSLog(@"Error happens");
        for (Student *student in matches) {
            [context deleteObject:student];
            NSLog(@"studentID: %@", student.studentID);
        }
    } else if (![matches count]) {
        student = [NSEntityDescription insertNewObjectForEntityForName:@"Student" inManagedObjectContext:context];

        NSString *studentID = (NSString *)infoDictionary[@"studentID"];
        int studentIDint = [studentID intValue];
        NSLog(@"studentID: %d", studentIDint);

        student.studentID = [NSNumber numberWithInt:studentIDint];
        student.nameFirst = infoDictionary[@"nameFirst"];
        student.nameLast  = infoDictionary[@"nameLast"];

        // Add this students portrait as a relationship
        Portrait *portrait = [Portrait portraitWithAssetURL:infoDictionary[@"PortraitAssetURL"] inManagedObjectContext:context];
        student.portrait = portrait;

        NSError *errorSave;
        [context save:&errorSave];
        NSLog(@"errorSave: %@", errorSave);

        NSLog(@"creating a new student, matches count: %lu", (unsigned long)[matches count]);
    } else {
        student = [matches lastObject];
        NSLog(@"fetching old one, count: %lu", (unsigned long)[matches count]);
    }

    return student;
}

@end

Answer 1

代码应如下所示:

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"EntityName"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"uniqueID == %@", newID]
[request setPredicate:predicate];
NSError *error = nil; 
NSArray *matches = [context executeFetchRequest:request error:&error];

if([matches count]){
    // update record
    SomeEnt *ent = [matches objectAtIndex:0];
    // ent set properties  
} 
else{
        // add new record
    SomeEnt *ent =  [NSEntityDescription insertNewObjectForEntityForName:@"EntityName" inManagedObjectContext:context];
    // ent set properties 
    // ...
}
NSError *error;
[context save:&error];