核心數據獲取請求錯誤

Question

我想基於屬性名稱獲取記錄。

我也試圖尋找類似的問題，但我不能夠找到解決辦法，所以我張貼問題...

，但我得到的異常而獲取：

[error] error: exception handling request: <NSSQLFetchRequestContext: 0x1c019a270> , keypath audio_1.m4a not found in entity <NSSQLEntity answer id=8> with userInfo of (null) 
CoreData: error: exception handling request: <NSSQLFetchRequestContext: 0x1c019a270> , keypath audio_1.m4a not found in entity <NSSQLEntity answer id=8> with userInfo of (null) 
2017-09-28 19:03:36.725060+0530 app[9684:891158] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'keypath audio_1.m4a not found in entity <NSSQLEntity answer id=8>' 

我的代碼：

let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: Entity) 

    if let predic = predicate_str{ 
     let predicate = NSPredicate(format: predic) 
     fetchRequest.predicate=predicate 
    } 

    do { 
     let arr = try appsession.managedObjectContext.fetch(fetchRequest) //CRASHED 


     // success ... 
    } catch let error as NSError { 
     // failure 
     print("Fetch failed: \(error.localizedDescription)") 
     return(nil,error) 
    } 

謝謝

Answer 1

您正在錯誤地構建謂詞字符串。值，以匹配必須引號內，所以你想建立這樣的：

let predicate = NSPredicate(format: "%K LIKE[c] %@", "imagePath", "audio1.m4a") 

解析爲以下謂詞字符串：

imagePath LIKE[c] "audio1.m4a" 

注意周圍的值，你」引號重新匹配，並且缺少屬性名稱周圍的引號。您當前的謂詞試圖查找其imagePath屬性與audio1.m4a屬性具有相同值的記錄，該屬性不起作用。