xcode - 传递给 Core Data 中的 setPropertiesToFetch 的无效键路径

Question

我在使用 setPropertiesToFetch 时收到此错误。这很奇怪，因为 info1 和 info2 确实存在于我的实体中。

    let fetchRequest = NSFetchRequest()
    let entityDescription = NSEntityDescription.entityForName("Table1", inManagedObjectContext: managedObjectContext)
    fetchRequest.resultType = .DictionaryResultType
    fetchRequest.returnsDistinctResults = true

    fetchRequest.propertiesToFetch = ["info1", "info2"]
    fetchRequest.includesSubentities = true
    fetchRequest.entity = entityDescription

    do {
        let result = try managedObjectContext.executeFetchRequest(fetchRequest)

        print(result)

    } catch {
        let fetchError = error as NSError
        print(fetchError)
    }

没有 propertiesToFetch 行我得到这个输出:

[{
    info1 = data1;
    info2 = data2;
    info3 = data3;
}, { 
...
}]

Answer 1

在使用 propertiesToFetch 之前需要设置实体。

fetchRequest.entity = entityDescription
fetchRequest.propertiesToFetch = ["info1", "info2"]
fetchRequest.includesSubentities = true