Question

我正在尝试在SQLite for Windows Runtime中实现自定义排序规则。

create_collation方法实现如下：

SQLITE_API int sqlite3_create_collation(
  sqlite3*, 
  const char *zName, 
  int eTextRep, 
  void *pArg,
  int(*xCompare)(void*,int,const void*,int,const void*)
);

到目前为止，我有以下C＃签名：

[DllImport("sqlite3", EntryPoint = "sqlite3_create_collation", CallingConvention = CallingConvention.Cdecl)]
public static extern int CreateCollation(IntPtr db, [MarshalAs(UnmanagedType.LPStr)] string name, int textRep, object state, Compare callback);

public delegate int Compare(object pCompareArg, int size1, IntPtr Key1, int size2, IntPtr Key2);

这是实施：

int i = CreateCollation(db, "unicode_nocase", SQLITE_UTF8, null, CompareMethod);

/* ... */

public static int CompareMethod(object o, int i1, IntPtr s1, int i2, IntPtr s2)
{
    return string.Compare(Marshal.PtrToStringUni(s1), Marshal.PtrToStringUni(s2));
}

应用程序编译没有错误。对create_collation的调用返回零（SQLITE_OK），但如果我在语句中使用排序规则，则会返回以下错误消息：

no such collation sequence: unicode_nocase

来源参考：https://github.com/doo/SQLite3-WinRT/tree/master/SQLite3Component

有人可以帮帮我吗？

谢谢！

Answer 1

经过一段时间环顾Mono.Android.SQLite，它也使用了SQLite的C实现，我找到了解决方案：

问题是对sqlite3_create_collation的调用有一个void *参数，我错误地将它定义为C＃中的对象，它应该是IntPtr。

我已经发布了下面的当前实现。我部分逆向设计了Mono实现的解决方案，它为每个要注册的排序规则调用sqlite3_create_collation两次 - 一次将参数eTextRep设置为SQLITE_UTF16LE，第二次使用SQLITE_UTF8。我只能想象这可能有助于SQLite核心找到存储字符串值的不同格式的快速实现。但是，当它们转换为C＃字符串时，它们需要不同的解码。

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate int CompareCallback(IntPtr pvUser, int len1, IntPtr pv1, int len2, IntPtr pv2);

    [DllImport("sqlite3", CallingConvention = CallingConvention.Cdecl)]
    private static extern int sqlite3_create_collation(IntPtr db, byte[] strName, int nType, IntPtr pvUser, CompareCallback func);

    private const int SQLITE_UTF8 = 1;
    private const int SQLITE_UTF16LE = 2;
    private const int SQLITE_UTF16BE = 3;
    private const int SQLITE_UTF16 = 4;    /* Use native byte order */
    private const int SQLITE_ANY = 5;    /* sqlite3_create_function only */
    private const int SQLITE_UTF16_ALIGNED = 8;    /* sqlite3_create_collation only */

    public void Register(IntPtr db)
    {
        if (db == IntPtr.Zero)
            throw new ArgumentNullException("db");

        //create null-terminated UTF8 byte array
        string name = Name;
        var nameLength = System.Text.Encoding.UTF8.GetByteCount(name);
        var nameBytes = new byte[nameLength + 1];
        System.Text.Encoding.UTF8.GetBytes(name, 0, name.Length, nameBytes, 0);

        //register UTF16 comparison
        int result = sqlite3_create_collation(db, nameBytes, SQLITE_UTF16LE, IntPtr.Zero, CompareUTF16);
        if (result != 0)
        {
            string msg = SQLite3.GetErrmsg(db);
            throw SQLiteException.New((SQLite3.Result)result, msg);
        }

        //register UTF8 comparison
        result = sqlite3_create_collation(db, nameBytes, SQLITE_UTF8, IntPtr.Zero, CompareUTF8);
        if (result != 0)
        {
            string msg = SQLite3.GetErrmsg(db);
            throw SQLiteException.New((SQLite3.Result)result, msg);
        }
    }

    private string GetUTF8String(IntPtr ptr, int len)
    {
        if (len == 0 || ptr == IntPtr.Zero)
            return string.Empty;

        if (len == -1)
        {
            do
            {
                len++;
            }
            while (Marshal.ReadByte(ptr, len) != 0);
        }

        byte[] array = new byte[len];
        Marshal.Copy(ptr, array, 0, len);

        return Encoding.UTF8.GetString(array, 0, len);
    }

    private string GetUTF16String(IntPtr ptr, int len)
    {
        if (len == 0 || ptr == IntPtr.Zero)
            return string.Empty;

        if (len == -1)
        {
            return Marshal.PtrToStringUni(ptr);
        }

        return Marshal.PtrToStringUni(ptr, len / 2);
    }

    internal int CompareUTF8(IntPtr ptr, int len1, IntPtr ptr1, int len2, IntPtr ptr2)
    {
        return Compare(GetUTF8String(ptr1, len1), GetUTF8String(ptr2, len2));
    }

    internal int CompareUTF16(IntPtr ptr, int len1, IntPtr ptr1, int len2, IntPtr ptr2)
    {
        return Compare(GetUTF16String(ptr1, len1), GetUTF16String(ptr2, len2));
    }

在SQLite for WinRT中实现自定义排序规则

1 个答案: