Firebase匹配数据解码失败：JSON序列化后无法解析为FirestoreMatch

从Firebase获取匹配数据时，解码环节失败，相同逻辑在获取用户资料时可正常运行。

相关代码片段 #

fetchMatches函数 #

func fetchMatches(onCompletion: @escaping (Result<[MatchModel], DomainError>) -> ()){
    db.collection("matches").whereField("usersMatched", arrayContains: userId!).getDocuments(completion: {doc, err in
        guard let documentSnapshot = doc, err == nil else{
            onCompletion(.failure(.downloadError))
            return
        }
        var matchList: [MatchModel] = []
        var count = 0
        let maxCount = documentSnapshot.documents.count
        var hasFailed = false
        for document in documentSnapshot.documents{
            if hasFailed{ break }
            
            let decoder = JSONDecoder()
            var dict = document.data()

            for (key, value) in dict {
                                
                if let value = value as? Timestamp {
                    
                    let formatter = DateFormatter()
                    let newValue = value.dateValue()
                    formatter.dateStyle = .short
                    formatter.timeStyle = .none
                    dict[key] = formatter.string(from: newValue)
                   }
                 }
        // 后续解码逻辑省略
    })
}

处理后的字典内容 #

Dictionary
["timestamp": "10/22/22", "usersMatched": <__NSArrayM 0x600002c61680>(
6euZHDmI7PMDcCmft5MfxUW27jI3,
tbcB0ay0YEgZcY9UsZ00WjZ9h893
)
]

错误信息 #

typeMismatch(Swift.Double, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "timestamp", intValue: nil)], debugDescription: "Expected to decode Double but found a string/data instead.", underlyingError: nil))

FirestoreMatch结构体定义 #

struct FirestoreMatch: Codable{
    let usersMatched: [String]
    let timestamp: Date
}

问题原因与解决方案 #

问题根源 #

你手动将Firestore的Timestamp类型转换为了字符串格式（如"10/22/22"），但FirestoreMatch的timestamp字段是Date类型。JSONDecoder默认会尝试将数字类型的时间戳解码为Date，遇到字符串时就会抛出类型不匹配错误。

解决方案1：使用Firebase内置的Codable解析（推荐） #

移除手动转换Timestamp为字符串的循环代码，直接用Firebase提供的data(as:)方法解析文档，它会自动处理Timestamp到Date的转换：

for document in documentSnapshot.documents{
    if hasFailed{ break }
    do {
        let match = try document.data(as: FirestoreMatch.self)
        matchList.append(match)
        // 后续处理逻辑
    } catch {
        hasFailed = true
        onCompletion(.failure(.downloadError))
    }
}

解决方案2：配置JSONDecoder解析自定义日期字符串 #

如果坚持要保留手动转换字符串的逻辑，需要给JSONDecoder设置对应的日期解析器，让它能识别你生成的字符串格式：

let decoder = JSONDecoder()
let dateFormatter = DateFormatter()
dateFormatter.dateStyle = .short
dateFormatter.timeStyle = .none
dateFormatter.locale = Locale(identifier: "en_US_POSIX") // 确保解析格式与生成时一致
decoder.dateDecodingStrategy = .formatted(dateFormatter)

// 之后再用该decoder解码数据
do {
    let data = try JSONSerialization.data(withJSONObject: dict)
    let match = try decoder.decode(FirestoreMatch.self, from: data)
    matchList.append(match)
} catch {
    hasFailed = true
    onCompletion(.failure(.downloadError))
}

内容的提问来源于stack exchange，提问作者Anthony contreras