我正在尝试使用 tracing 在我的代码中调试一些 SQLite 查询只需将发生的一切记录到控制台，但似乎几乎没有任何信息——谷歌搜索“sqlite3_trace_v2 swift”只返回两页结果，除了上面的链接外，没有任何帮助。使用以下代码，我能够让它至少运行跟踪回调:

func traceSQL (database: OpaquePointer?) {
    var pointer: OpaquePointer?
    func traceCallback (mask: UInt32, pointer: UnsafeMutableRawPointer?, query: UnsafeMutableRawPointer?, result: UnsafeMutableRawPointer?) -> Int32 {
        print("SQLite Trace:")

        if let query = query?.load(as: UnsafePointer<Int8>.self) {
            print(String(cString: query))
        } else {
            print("Could not load query.")
        }

        if let result = result?.load(as: UnsafePointer<Int8>.self) {
            print(String(cString: result))
        } else {
            print("Could not load result.")
        }

        return 0
    }
    sqlite3_trace_v2(database, 15, traceCallback as @convention(c) (UInt32, UnsafeMutableRawPointer?, UnsafeMutableRawPointer?, UnsafeMutableRawPointer?) -> Int32, &pointer)
}

但我无法弄清楚如何处理该函数的输出 - 目前，它只是打印出一串不可读的字符，而我之前的尝试甚至没有做到这一点。我怀疑至少部分问题是我真的不知道如何在 Swift 中使用 UnsafeMutableRawPointer(可用信息中似乎缺少其他东西)。

tl;dr:如何记录来自 SQLite 的跟踪结果？

最佳答案

您代码中的主要错误是您取消引用 原始指针 传递给回调而不是重新解释(转换)它们。 这些指针的含义对于不同的人也是不同的 事件。

下面是一个如何跟踪各种事件以及如何转换的例子 使用文字闭包指向“正确”类型的原始指针 作为回调。解释 p 和 x 含义的注释 参数取自 SQL Trace Event Codes .

let traceMask = SQLITE_TRACE_STMT|SQLITE_TRACE_PROFILE|SQLITE_TRACE_ROW|SQLITE_TRACE_CLOSE

sqlite3_trace_v2(database, UInt32(traceMask), { (reason, context, p, x) -> Int32 in
    switch Int32(reason) {
    case SQLITE_TRACE_STMT:
        // The P argument is a pointer to the prepared statement.
        // The X argument is a pointer to a string which is the unexpanded SQL text 
        guard
            let pStmt = OpaquePointer(p),
            let cSql = x?.assumingMemoryBound(to: CChar.self)
        else {
            return 0
        }

        let sql = String(cString: cSql) // The unexpanded SQL text
        let expandedSql = String(cString: sqlite3_expanded_sql(pStmt)) // The expanded SQL text
        print("SQLITE_TRACE_STMT:", expandedSql)

    case SQLITE_TRACE_PROFILE:
        // The P argument is a pointer to the prepared statement and the X argument points
        // to a 64-bit integer which is the estimated of the number of nanosecond that the
        // prepared statement took to run.
        guard
            let pStmt = OpaquePointer(p),
            let duration = x?.load(as: UInt64.self)
        else {
            return 0
        }

        let milliSeconds = Double(duration)/Double(NSEC_PER_MSEC)
        let sql = String(cString: sqlite3_sql(pStmt)) // The unexpanded SQL text
        print("SQLITE_TRACE_PROFILE:", milliSeconds, "ms for statement:", sql)

    case SQLITE_TRACE_ROW:
        // The P argument is a pointer to the prepared statement and the X argument is unused.
        guard
            let pStmt = OpaquePointer(p)
        else {
            return 0
        }

        print("SQLITE_TRACE_ROW")

    case SQLITE_TRACE_CLOSE:
        // The P argument is a pointer to the database connection object and the X argument is unused.
        guard
            let database = OpaquePointer(p)
        else {
            return 0
        }

        print("SQLITE_TRACE_CLOSE")

    default:
        break
    }
    return 0
}, nil)

当然，您可以将跟踪模式限制为您所关注的事件 很有趣，例如

let traceMask = SQLITE_TRACE_STMT

仅跟踪准备好的语句。

关于swift - 用于日志记录的 SQLite 跟踪，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/43593618/