小编Abd*_*ekh的帖子

我有用户模式，其中人员字段包含viewers属性，该属性包含一个 ObjectId 数组作为用户集合本身的引用，例如

{
    "username": "user1",
    "password": "password",
    "email": "user1@gmail.com",
    "people": [{
            "id": 1,
            "viewers": ["ObjectId....", "ObjectId...."]
        },
        {
            "id": 2,
            "viewers": ["ObjectId....", "ObjectId...."]
        }
    ]
}

我需要做的是$lookup对于查看器内的每个元素，问题是当我使用下面的管道时，为每个文档推送相同的查看器

{
  $unwind: {
    path: "$people.viewers",
    preserveNullAndEmptyArrays: true
  }
},
{
  $lookup: {
    from: "users",
    localField: "people.viewers",
    foreignField: "_id",
    as: "people"
  }
},
{
  $unwind: {
    path: "$viewers",
    preserveNullAndEmptyArrays: true
  }
},
{
  $project: {
    username: 1,        
    "viewers.username": 1    
  }
},
{
  $group: {
    _id: "$_id",
    username: { $first: …

尝试textField获得信用卡的到期日期，下面的代码正常工作只是想改变行为，目前当您从第三个数字/字符输入时，将添加为到期格式。如果我想在用户输入第二个数字后添加/字符怎么办，例如如果用户输入 01 直接插入分隔符

open func reformatAsExpiration(_ textField: UITextField) {
        guard let string = textField.text else { return }
        let expirationString = String(ccrow.expirationSeparator)
        let cleanString = string.replacingOccurrences(of: expirationString, with: "", options: .literal, range: nil)
        if cleanString.length >= 3 {
            let monthString = cleanString[Range(0...1)]
            var yearString: String
            if cleanString.length == 3 {
                yearString = cleanString[2]
            } else {
                yearString = cleanString[Range(2...3)]
            }
            textField.text = monthString + expirationString + yearString
        } else {
            textField.text = cleanString
        } …