如何使用NSExpression通过自定义函数设置NSFetchRequest propertiesToFetch

// 创建自定义函数的NSExpression对象
let functionExpression = NSExpression(expressionFunction: NSExpression(forConstantValue: "uppercase:"), arguments: [NSExpression(forKeyPath: "name")])

// 创建NSExpressionDescription对象
let expressionDescription = NSExpressionDescription()
expressionDescription.name = "uppercaseName"
expressionDescription.expression = functionExpression

// 创建NSFetchRequest对象
let fetchRequest = NSFetchRequest<NSFetchRequestResult>()
fetchRequest.entity = NSEntityDescription.entity(forEntityName: "Person", in: managedObjectContext)
fetchRequest.propertiesToFetch = [expressionDescription]

// 执行查询请求
do {
    let results = try managedObjectContext.fetch(fetchRequest)
    // 处理查询结果
} catch {
    // 处理错误
}