NSfetchRequest 啥都不返回

Posted 2023-03-04

【中文标题】NSfetchRequest 啥都不返回

【英文标题】：NSfetchRequest return nothingNSfetchRequest 什么都不返回

【发布时间】：2019-07-08 11:52:58

【问题描述】：

当从核心数据库中获取数据并同时更新同一实体的数据时，fetchRequest 返回 nil

let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Abc")
        fetchRequest.predicate = NSPredicate(format: "id = %@ ", productID)

    do 
        let product = try mainContext.fetch(fetchRequest).first
        return product as? Products
     catch _ as NSError 
        //print("Could not fetch. \(error), \(error.userInfo)")
        return nil
    

【参考方案1】：

实体与结果的转换类型不匹配

要么是

let fetchRequest = NSFetchRequest(entityName: "Abc")

...

do 
    let product = try mainContext.fetch(fetchRequest).first
    return product as? Abc

或

 let fetchRequest = NSFetchRequest(entityName: "Products")

 do 
    let product = try mainContext.fetch(fetchRequest).first
    return product as? Products

请以单数形式命名实体。从语义上讲，你投了product as? Product

【讨论】：

实体名称是 Products 而不是 ABC

然后按照第二个建议。