Get the generated SQL statement from a SqlCommand object?

For logging purposes, I'm afraid there's no nicer way of doing this but to construct the string yourself:

string query = cmd.CommandText;

foreach (SqlParameter p in cmd.Parameters)
{
    query = query.Replace(p.ParameterName, p.Value.ToString());
}

You can't, because it does not generate any SQL.

The parameterized query (the one in CommandText) is sent to the SQL Server as the equivalent of a prepared statement. When you execute the command, the parameters and the query text are treated separately. At no point in time a complete SQL string is generated.

You can use SQL Profiler to take a look behind the scenes.

If you're using SQL Server, you could use SQL Server Profiler (if you have it) to view the command string that is actually executed. That would be useful for copy/paste testing purpuses but not for logging I'm afraid.

Late answer, I know but I too wanted this so I could log the SQL. The following is short and meets my needs.

The following produces SQL you can copy/paste in SSMS (it replaces the parameters with the values properly). You can add more types but this meets all I use in this case.

    private static void LogSQL(SqlCommand cmd)
        {
            string query = cmd.CommandText;

            foreach (SqlParameter prm in cmd.Parameters)
            {
                switch (prm.SqlDbType)
                {
                    case SqlDbType.Bit:
                        int boolToInt = (bool)prm.Value ? 1 : 0;
                        query = query.Replace(prm.ParameterName, string.Format("{0}", (bool)prm.Value ? 1 : 0));
                        break;
                    case SqlDbType.Int:
                        query = query.Replace(prm.ParameterName, string.Format("{0}", prm.Value));
                        break;
                    case SqlDbType.VarChar:
                        query = query.Replace(prm.ParameterName, string.Format("'{0}'", prm.Value));
                        break;
                    default:
                        query = query.Replace(prm.ParameterName, string.Format("'{0}'", prm.Value));
                        break;
                }
            }

            // the following is my how I write to my log - your use will vary
            logger.Debug("{0}", query);

            return;
        }

Now I can log the SQL just before I execute it:

LogSQL(queryCmd)
queryCmd.ExecuteNonQuery()

Profiler is hands-down your best option.

You might need to copy a set of statements from profiler due to the prepare + execute steps involved.

If your database was Oracle and the sql text contains dynamic variables named like :1,:2 ,... then you can use:

string query = cmd.CommandText;
int i = 1;
foreach (OracleParameter p in cmd.Parameters)
  {
    query = query.Replace(":"+i.ToString(),((p.Value==null)?"":p.Value.ToString()));
    i++;
  }

needed to cover non-Stored procedures too so I augmented CommandAsSql library (see comments under @Flapper's answer above) with this logic:

    private static void CommandAsSql_Text(this SqlCommand command, System.Text.StringBuilder sql)
    {
        string query = command.CommandText;

        foreach (SqlParameter p in command.Parameters)
            query = Regex.Replace(query, "\\B" + p.ParameterName + "\\b", p.ParameterValueForSQL()); //the first one is \B, the 2nd one is \b, since ParameterName starts with @ which is a non-word character in RegEx (see https://stackoverflow.com/a/2544661)

        sql.AppendLine(query);
    }

the pull request is at: https://github.com/jphellemons/CommandAsSql/pull/3/commits/527d696dc6055c5bcf858b9700b83dc863f04896

the Regex idea was based on @stambikk's and EvZ's comments above and the "Update:" section of https://stackoverflow.com/a/2544661/903783 that mentions "negative look-behind assertion". The use of \B instead of \b for word boundary detection at the start of the regular expression is because the p.parameterName will always start with a "@" which is not a word character.

note that ParameterValueForSQL() is an extension method defined at the CommandAsSql library to handle issues like single-quoting string parameter values etc.

If you will convert the commandtext:

Private Function ConvToNonParm(ByRef Cmd As SqlClient.SqlCommand) As String
    For myCnt As Int16 = 1 To Cmd.Parameters.Count
        Dim myVal As String = Cmd.Parameters(myCnt - 1).Value
        Select Case Cmd.Parameters(myCnt - 1).SqlDbType
            Case SqlDbType.Char, SqlDbType.NChar, SqlDbType.VarChar, SqlDbType.NChar, SqlDbType.NVarChar 'and so on
                myVal = "'" & myVal & "'"
                'Case "others...."

            Case Else
                'please assing
        End Select
        Cmd.CommandText = Replace(Cmd.CommandText, Cmd.Parameters(myCnt - 1).ToString, myVal)
    Next
    Cmd.Parameters.Clear()
    Return Cmd.CommandText
End Function

Now you can get the non parameter commandtext as follows:

    myCmd.CommandText = "UPDATE someTable SET Value = @Value"
    myCmd.CommandText &= " WHERE Id = @Id"
    myCmd.Parameters.AddWithValue("@Id", 1234)
    myCmd.Parameters.AddWithValue("@Value", "myValue")

    myCmd.CommandText = ConvToNonParm(myCmd)

and the Result is "UPDATE someTable SET Value = 'myValue' WHERE Id = 1234" without parameter anymore

Extended Kon's code to help debug a stored procedure:

    private void ExtractSqlCommandForDebugging(SqlCommand cmd)
    {
        string sql = "exec " + cmd.CommandText;
        bool first = true;
        foreach (SqlParameter p in cmd.Parameters)
        {
            string value = ((p.Value == DBNull.Value) ? "null"
                            : (p.Value is string) ? "'" + p.Value + "'"
                            : p.Value.ToString());
            if (first)
            {
                sql += string.Format(" {0}={1}", p.ParameterName, value);
                first = false;
            }
            else
            {
                sql += string.Format("\n , {0}={1}", p.ParameterName, value);
            }
        }
        sql += "\nGO";
        Debug.WriteLine(sql);
    }

In my first test case, it generated:

exec dbo.MyStoredProcName @SnailMail=False
 , @Email=True
 , @AcceptSnailMail=False
 , @AcceptEmail=False
 , @DistanceMiles=-1
 , @DistanceLocationList=''
 , @ExcludeDissatisfied=True
 , @ExcludeCodeRed=True
 , @MinAge=null
 , @MaxAge=18
 , @GenderTypeID=-1
 , @NewThisYear=-1
 , @RegisteredThisYear=-1
 , @FormersTermGroupList=''
 , @RegistrationStartDate=null
 , @RegistrationEndDate=null
 , @DivisionList='25'
 , @LocationList='29,30'
 , @OneOnOneOPL=-1
 , @JumpStart=-1
 , @SmallGroup=-1
 , @PurchasedEAP=-1
 , @RedeemedEAP=-1
 , @ReturnPlanYes=False
 , @MinNetPromoter=-1
 , @MinSurveyScore=-1
 , @VIPExclusionTypes='-2'
 , @FieldSelectionMask=65011584
 , @DisplayType=0
GO

You will probably need to add some more conditional "..is..." type assignments, e.g. for dates and times.

From parameter command to non parameter command, You Can change this one

Using cmd As SqlCommand = Connection.CreateCommand
    cmd.CommandText = "UPDATE someTable SET Value = @Value"
    cmd.CommandText &= " WHERE Id = @Id"
    cmd.Parameters.AddWithValue("@Id", 1234)
    cmd.Parameters.AddWithValue("@Value", "myValue")
    cmd.ExecuteNonQuery
End Using

To

Private sub Update( byval myID as Int32, byval myVal as String)
    Using cmd As SqlCommand = Connection.CreateCommand
        cmd.CommandText = "UPDATE someTable SET Value = '" & myVaL & "'" & _
                          " WHERE Id = " & myID  
        cmd.ExecuteNonQuery
    End Using
End sub