ios - 按名称获取实体并使用 CoreData 创建关系

Question

我正在尝试在两个实体 Mensagem 和 Category 之间创建关系，但出现以下错误:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unacceptable type of value for to-many relationship: property = "mensagemParaCategorias"; desired type = NSSet; given type = __NSArrayI; ...
).'

我尝试做的是:创建一个实体属性(categoriaAtual)，然后尝试按名称获取实体，并将实体设置为获取的结果，然后创建关系。

这是我的代码。

创建初始日期.h

#import <Foundation/Foundation.h>
#import "Mensagens.h"
#import "Categorias.h"

@interface createInitialData : NSObject

@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, strong) NSFetchedResultsController *fetchedResultsController;
@property (nonatomic) Categorias *categoriaAtual;

-(void)createMessage:(NSString *)mensagem ComAutor:(NSString *)autor;

创建初始数据.m

-(void)createMessage:(NSString *)mensagem ComAutor:(NSString *)autor {
    Mensagens *novaMensagem = (Mensagens *)[NSEntityDescription insertNewObjectForEntityForName:@"Mensagens" inManagedObjectContext:self.managedObjectContext];

    [novaMensagem setMensagem:mensagem];
    [novaMensagem setAutor:autor];
    NSDate *agora = [NSDate date];
    [novaMensagem setDataCriada:agora];
    [self categoria:@"Posts"];

    novaMensagem.mensagemParaCategorias = _categoriaAtual; // This is where i try to create the relation between the 2 entities. 

    NSError *error = nil;
    NSManagedObjectContext *context = self.managedObjectContext;

    if (![context save:&error]) {
        NSLog(@"Error! %@", error);
    }

}



-(void)categoria:(NSString *)nomeCategoria {
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc]init];


    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Categorias" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"categoria == '%@'", nomeCategoria];
    [fetchRequest setPredicate:predicate];

    NSError *error = nil;

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

    if (fetchedObjects == nil) {
        NSLog(@"Problem! %@", error);
    } else {
        NSLog(@"Objetos %@", fetchedObjects);
        _categoriaAtual = fetchedObjects;
    }

}

Answer 1

mensagemParaCategorias

是一对多关系，但您正在将指针分配给一个不是 NSSet 实例的对象。 Xcode 有一个选项可以在您的托管对象子类上生成方法，以将对象添加到一对多关系中。