自动生成不重复的ID，利用2分查找，生成中间缺少的ID值，保持id的连续性
#region 生成不重复的Id
/// <summary>
/// 根据参数生成一个在表内指定字段的唯一字符串
/// </summary>
/// <param name="length">字符串长度</param>
/// <param name="tableName">表名</param>
/// <param name="keyFieldName">字段</param>
/// <returns>返回长度为length的字符串</returns>
private static OracleDataAdapter oraAdp = null;
public string GenerateKey(int length, string tableName, string keyFieldName)
{
// return "";
ConnectionStringSettings settings = ConfigurationManager.ConnectionStrings["gdfsys"];
string connectionString = settings.ConnectionString;
if (oraAdp == null)
{
oraAdp = new OracleDataAdapter("select 1 from dual", connectionString);
}
oraAdp.SelectCommand.CommandText = "select " + keyFieldName + " from " + tableName + " order by " + keyFieldName;
DataTable dt = new DataTable();
oraAdp.Fill(dt);
// 使用二分法查找
int lower = 1;
// 没有数据则默认为1
if (dt != null && dt.Rows.Count > 0)
{
// 如果最后一条的ID等于记录数，则说明中间没有删除的ID，
if (Convert36To10(dt.Rows[dt.Rows.Count - 1][0].ToString()) == dt.Rows.Count)
{
lower = dt.Rows.Count;
}
else
{
int upper = dt.Rows.Count - 1;
while (lower <= upper)
{
int m = (lower + upper) / 2;
if (m > 0 && Convert36To10(dt.Rows[m - 1][0].ToString()) > m)
{
upper = m - 1;
}
else
{
lower = m + 1;
}
}
lower = upper;
}
lower++;
}
return GetKey(length, Convert10To36(lower));
}
public string Convert10To36(int num)
{
string value = "";
if (num == 0)
{
value = "0";
}
else
{
while (num > 0)
{
int n = num % 36;
value = GetCharValue(n) + value;
num = num - n;
if (num > 0)
{
num = num / 36;
}
}
}
return value;
}
private string GetCharValue(int num)
{
return num.ToString();
}
public string GetKey(int length, string num)
{
while (num.Length < length)
{
num = "0" + num;
}
return num;
}
public int Convert36To10(string num)
{
int value = 0;
for (int i = 0; i < num.Length; i++)
{
//value = value + GetIntValue(num[num.Length - 1 - i]) * ((int)Math.Pow(10, i));
//value += GetIntValue(num[num.Length - 1 - i]);
value += GetIntValue(num[num.Length - 1 - i]) * ((int)Math.Pow(10, i));
}
return value;
}
private int GetIntValue(char num)
{
int GetValue = 0;
if (num <= '9')
{
GetValue = int.Parse(num.ToString());
}
return GetValue;
}
#endregion
