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  DeriveParameters方法

  先说简单的一个。DeriveParameters是SqlCommandBuilder类的一个公共方法，提供一个SqlCommannd的参数，该Command对象作为获取到的Parameters的存放容器。其实SqlCommand本身就有一个DeriveParameters的方法，但是它是内部方法，而SqlCommandBuilder.DeriveParameters就是封装了该方法的调用：

1public static void DeriveParameters(SqlCommand command)
2{
3      SqlConnection.SqlClientPermission.Demand();
4      if (command == null)
5      {
6            // throw an exception
7      }
8      command.DeriveParameters();
9}

  来看一下SqlCommand的DeriveParameters方法：

1internal void DeriveParameters()
2{
3
4      // Validate command type(is storedprocedure?) and command info
 5
6
7      // Retrieve command text detail
 8      string[] txtCommand = ADP.ParseProcedureName(this.CommandText);
9
10      SqlCommand cmdDeriveCommand = null;
11
12      this.cmdText = "sp_procedure_params_rowset";
13      if (txtCommand[1] != null)
14      {
15            this.cmdText = "[" + txtCommand[1] + "].." + this.cmdText;
16
17            if (txtCommand[0] != null)
18            {
19                  this.cmdText = txtCommand[0] + "." + this.cmdText;
20            }
21
22            cmdDeriveCommand = new SqlCommand(this.cmdText, this.Connection);
23      }
24      else
25      {
26            cmdDeriveCommand = new SqlCommand(this.cmdText, this.Connection);
27      }
28      cmdDeriveCommand.CommandType = CommandType.StoredProcedure;
29      cmdDeriveCommand.Parameters.Add(new SqlParameter("@procedure_name", SqlDbType.NVarChar, 0xff));
30      cmdDeriveCommand.Parameters[0].Value = txtCommand[3];
31      ArrayList parms = new ArrayList();
32      try
33      {
34            try
35            {
36                  using (SqlDataReader drParam = cmdDeriveCommand.ExecuteReader())
37                  {
38                        SqlParameter parameter = null;
39                        while (drParam.Read())
40                        {
41                              parameter = new SqlParameter();
42                              parameter.ParameterName = (string) drParam["PARAMETER_NAME"];
43                              parameter.SqlDbType = MetaType.GetSqlDbTypeFromOleDbType((short) drParam["DATA_TYPE"], (string) drParam["TYPE_NAME"]);
44                              object len = drParam["CHARACTER_MAXIMUM_LENGTH"];
45                              if (len is int)
46                              {
47                                    parameter.Size = (int) len;
48                              }
49                              parameter.Direction = this.ParameterDirectionFromOleDbDirection((short) drParam["PARAMETER_TYPE"]);
50                              if (parameter.SqlDbType == SqlDbType.Decimal)
51                              {
52                                    parameter.Scale = (byte) (((short) drParam["NUMERIC_SCALE"]) & 0xff);
53                                    parameter.Precision = (byte) (((short) drParam["NUMERIC_PRECISION"]) & 0xff);
54                              }
55                              parms.Add(parameter);
56                        }
57                  }
58            }
59            finally
60            {
61                  cmdDeriveCommand.Connection = null;
62            }
63      }
64      catch
65      {
66            throw;
67      }
68
69      if (params.Count == 0)
70      {
71            // throw an exception that current storedprocedure does not exist
72      }
73
74      this.Parameters.Clear();
75      foreach (object parm in parms)
76      {
77            this._parameters.Add(parm);
78      }
79}