I need set the parameter date for compare on a SQL Server table.
Where the day, month and year he will add the QUANTIDADE and weight of fish.
But giving this a mistake and falling in the catch and can not set it.
DATA_REGISTRO is a Date datatype in SQL Server.
Code:
public void Search_DATE(string param_date)
{
SqlDataReader objReader;
SqlCommand objcmd = null;
vsql = "SELECT [IDCADASTRO],[RGP],[PEIXE],[PESO],[QUANTIDADE],[DATA_REGISTRO] FROM cadastro WHERE DATA_REGISTRO LIKE #DATA_REGISTRO";
if (this.Conectar())
{
try
{
objcmd = new SqlCommand(vsql, objCon);
objcmd.Parameters.Add(new SqlParameter("#DATA_REGISTRO", param_date));
objReader = objcmd.ExecuteReader();
if (objReader.Read())
{
valor.retorna_date_time = objReader.GetDateTime(5).ToString;
}
}
catch (SqlException erro)
{
throw erro;
}
finally
{
this.Desconectar();
}
}
Global Variable
private static string date_time;
public string retorna_date_time
{
get { return date_time; }
set { date_time = value; }
}
DATA_REGISTRO is a Date type on SQL
However, you are supplying a string parameter
public string retorna_date_time
objcmd.Parameters.Add(new SqlParameter("#DATA_REGISTRO", param_date));
Instead, supply a DateTime parameter
DateTime dtParam = DateTime.Parse(param_date);
objcmd.Parameters.Add(new SqlParameter("#DATA_REGISTRO", dtParam));
Also, it is not a good idea to catch an exception unless you will do something with it
catch (SqlException erro)
{
throw erro;
}
I understand you may have that line in there for debugging, but remove it from your final code unless there is something you can do with the exception.
Pass the Date of you param_date.
objcmd.Parameters.Add(new SqlParameter("#DATA_REGISTRO", Convert.ToDateTime(param_date).Date));
I need verify the Parameter RGP, PEIXE, DATA_REGISTRO for my method return true. But on PEIXE parameter this giving error:
Expects 'PEIXE' parameter, which was not provided.
PEIXE is a Varchar type on SQL, RGP is a Int type and DATA_REGISTRO is a Date type.
public bool Search_RGP_Cadastro(int param_RGP, string param_date, string param_peixe)
{
SqlDataReader objReader;
SqlCommand objcmd = null;
vsql = "SELECT [RGP], [PEIXE], [PESO], [QUANTIDADE], [DATA_REGISTRO] FROM cadastro WHERE RGP = #RGP and PEIXE = #PEIXE and DATA_REGISTRO = #DATA_REGISTRO";
if (this.Conectar())
{
try
{
DateTime dtParam = DateTime.Parse(param_date);
objcmd = new SqlCommand(vsql, objCon);
objcmd.Parameters.Add(new SqlParameter("#RGP", param_RGP));
objcmd.Parameters.Add(new SqlParameter("#PEIXE", param_peixe));
objcmd.Parameters.Add(new SqlParameter("#DATA_REGISTRO", dtParam));
objReader = objcmd.ExecuteReader();
if (objReader.Read())
{
valor.retorna_RGP = objReader.GetInt32(0);
valor.retorna_nome_peixe = objReader.GetString(1);
valor.retorna_peso = objReader.GetDouble(2);
valor.retorna_Quantidade = objReader.GetInt32(3);
valor.retorna_date_time = objReader.GetDateTime(4);
}
return true;
}
catch
{
throw;
}
finally
{
this.Desconectar();
}
}
else
return false;
}
I'd wrap your param_peixe in single quotes, like this:
objcmd.Parameters.Add(new SqlParameter("#PEIXE", "'" + param_peixe + "'"));
It wouldn't be the first time I've seen SQL reject the use of a string as a VARCHAR.
I have an issue. please help to solve my problem
I have a SQL function
function [dbo].[fnKudishikaAmt]
(#ParishName nvarchar(100), #Hno int, #dateto datetime = Null)
Returns Decimal(15,2)
This function shows proper result by using the execute command
Select dbo.fnKudishikaAmt('St.George Malankara Catholic Church', 29, default)
My requirement is this function should be called from C#
I am getting the error
Conversion failed when converting datetime from character string
Code:
public double kudishikatotal(string ParishName, Int32 HouseNo)
{
String SQLText = "select ChurchDB.dbo.fnKudishikaAmt(#ParishName, #Hno, #dateto) as fnresult";
SqlCommand cmd = new SqlCommand(SQLText);
cmd.CommandType = CommandType.Text;
cmd.Parameters.AddWithValue("#ParishName", ParishName);
cmd.Parameters.AddWithValue("#Hno", HouseNo);
cmd.Parameters.AddWithValue("#dateto", "default");
string rval = GetSingleValue(cmd);
double kudiamt = 0;
if (rval != null)
{
kudiamt = Convert.ToDouble(rval);
}
return kudiamt;
}
private static string GetSingleValue(SqlCommand cmd)
{
string ConString = connectionstring();
string returnvalue = "";
using (SqlConnection con = new SqlConnection(ConString))
{
cmd.Connection = con;
con.Open();
returnvalue = cmd.ExecuteScalar().ToString();
con.Close();
}
return returnvalue;
}
If you've declared default value for parameter in stored procedure - then you can just not pass this parameter from c# code at all, and in this case it will have default value.
In your case exception thrown because it's impossible to convert string "default" to SqlDateTime which is your parameter type.
YOu can use if condition while sending the datetime parameter.
if(some condition)
{
cmd.Parameters.AddWithValue("#dateto", dateTimeValue);
}
Here datetimeValue is the value you want to pass. So you will be passing dateTimeValue only if required.
The error is due to the string "default" you passed.
I have 2 controls in my form,one is an int and the other is a float,I tried to convert with the "Convert.toString()" method but it didn't work and I get all the time a null value
this is my code:
string req = "select coef from amortissement where id_amort =#p";
textBox4.Text =Convert.ToString(GetRecordsetValue(req, textBox1.Text) as String)
req = "select Plan from amortissement where id_amort =#p";
textBox3.Text =Convert.ToString(GetRecordsetValue(req, textBox1.Text) as String);
this is the GetRecordsetValue method:
private Object GetRecordsetValue(string req, string sValParam)
{
// ExecuteScalar est optimisée pour récupérer une seule valeur
SqlCommand cmd = null;
try
{
cmd = new SqlCommand(req, con);
cmd.Parameters.AddWithValue("#p", sValParam);
return cmd.ExecuteScalar();
}
catch
{
return String.Empty;
}
finally
{
cmd.Dispose();
}
}
thanks for Help
The code in GetRecordsetValue returns NULL if your query doesn't find any record matching the WHERE condition. The null value returned is passed back to Convert.ToString() and this throws the exception
string req = "select coef from amortissement where id_amort =#p";
object result = GetRecordsetValue(req, textBox1.Text);
if(result != null)
{
textBox4.Text = Convert.ToString(result);
}
else
{
// and/or a message to the user to correct its inputs.
textBox4.Text = "";
}
There is also the problem of the value passed inside the GetRecordsetValue. This value is passed as a string and it is added inside the parameter collection as a string datatype. If the field id_amort is not a string (as it seems from its name) then it is highly probable that your query cannot find the record.
I suggest to create different overloads of GetRecordsetValue. One that takes an integer for example
I am using the following SQL query and the ExecuteScalar() method to fetch data from an Oracle database:
sql = "select username from usermst where userid=2"
string getusername = command.ExecuteScalar();
It is showing me this error message:
System.NullReferenceException: Object reference not set to an instance of an object
This error occurs when there is no row in the database table for userid=2.
How should I handle this situation?
According to MSDN documentation for DbCommand.ExecuteScalar:
If the first column of the first row in the result set is not found, a
null reference (Nothing in Visual Basic) is returned. If the value in
the database is null, the query returns DBNull.Value.
Consider the following snippet:
using (var conn = new OracleConnection(...)) {
conn.Open();
var command = conn.CreateCommand();
command.CommandText = "select username from usermst where userid=2";
string getusername = (string)command.ExecuteScalar();
}
At run-time (tested under ODP.NET but should be the same under any ADO.NET provider), it behaves like this:
If the row does not exist, the result of command.ExecuteScalar() is null, which is then casted to a null string and assigned to getusername.
If the row exists, but has NULL in username (is this even possible in your DB?), the result of command.ExecuteScalar() is DBNull.Value, resulting in an InvalidCastException.
In any case, the NullReferenceException should not be possible, so your problem probably lies elsewhere.
First you should ensure that your command object is not null. Then you should set the CommandText property of the command to your sql query. Finally you should store the return value in an object variable and check if it is null before using it:
command = new OracleCommand(connection)
command.CommandText = sql
object userNameObj = command.ExecuteScalar()
if (userNameObj != null)
string getUserName = userNameObj.ToString()
...
I'm not sure about the VB syntax but you get the idea.
I just used this:
int? ReadTerminalID()
{
int? terminalID = null;
using (FbConnection conn = connManager.CreateFbConnection())
{
conn.Open();
FbCommand fbCommand = conn.CreateCommand();
fbCommand.CommandText = "SPSYNCGETIDTERMINAL";
fbCommand.CommandType = CommandType.StoredProcedure;
object result = fbCommand.ExecuteScalar(); // ExecuteScalar fails on null
if (result.GetType() != typeof(DBNull))
{
terminalID = (int?)result;
}
}
return terminalID;
}
The following line:
string getusername = command.ExecuteScalar();
... will try to implicitly convert the result to string, like below:
string getusername = (string)command.ExecuteScalar();
The regular casting operator will fail if the object is null.
Try using the as-operator, like this:
string getusername = command.ExecuteScalar() as string;
sql = "select username from usermst where userid=2"
var _getusername = command.ExecuteScalar();
if(_getusername != DBNull.Value)
{
getusername = _getusername.ToString();
}
Check out the example below:
using System;
using System.Data;
using System.Data.SqlClient;
class ExecuteScalar
{
public static void Main()
{
SqlConnection mySqlConnection =new SqlConnection("server=(local)\\SQLEXPRESS;database=MyDatabase;Integrated Security=SSPI;");
SqlCommand mySqlCommand = mySqlConnection.CreateCommand();
mySqlCommand.CommandText ="SELECT COUNT(*) FROM Employee";
mySqlConnection.Open();
int returnValue = (int) mySqlCommand.ExecuteScalar();
Console.WriteLine("mySqlCommand.ExecuteScalar() = " + returnValue);
mySqlConnection.Close();
}
}
from this here
SQL NULL value
equivalent in C# is DBNull.Value
if a NULLABLE column has no value, this is what is returned
comparison in SQL: IF ( value IS NULL )
comparison in C#: if (obj == DBNull.Value)
visually represented in C# Quick-Watch as {}
Best practice when reading from a data reader:
var reader = cmd.ExecuteReader();
...
var result = (reader[i] == DBNull.Value ? "" : reader[i].ToString());
In my experience, there are some cases the returned value can be missing and thus execution fails by returning null. An example would be
select MAX(ID) from <table name> where <impossible condition>
The above script cannot find anything to find a MAX in. So it fails. In these such cases we must compare the old fashion way (compare with C# null)
var obj = cmd.ExecuteScalar();
var result = (obj == null ? -1 : Convert.ToInt32(obj));
If you either want the string or an empty string in case something is null, without anything can break:
using (var cmd = new OdbcCommand(cmdText, connection))
{
var result = string.Empty;
var scalar = cmd.ExecuteScalar();
if (scalar != DBNull.Value) // Case where the DB value is null
{
result = Convert.ToString(scalar); // Case where the query doesn't return any rows.
// Note: Convert.ToString() returns an empty string if the object is null.
// It doesn't break, like scalar.ToString() would have.
}
return result;
}
Always have a check before reading row.
if (SqlCommand.ExecuteScalar() == null)
{
}
This is the easiest way to do this...
sql = "select username from usermst where userid=2"
object getusername = command.ExecuteScalar();
if (getusername!=null)
{
//do whatever with the value here
//use getusername.toString() to get the value from the query
}
In your case either the record doesn't exist with the userid=2 or it may contain a null value in first column, because if no value is found for the query result used in SQL command, ExecuteScalar() returns null.
Alternatively, you can use DataTable to check if there's any row:
SqlCommand cmd = new SqlCommand("select username from usermst where userid=2", conn);
SqlDataAdapter adp = new SqlDataAdapter(cmd);
DataTable dt = new DataTable();
adp.Fill(dt);
string getusername = "";
// assuming userid is unique
if (dt.Rows.Count > 0)
getusername = dt.Rows[0]["username"].ToString();
private static string GetUserNameById(string sId, string connStr)
{
System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection(connStr);
System.Data.SqlClient.SqlCommand command;
try
{
// To be Assigned with Return value from DB
object getusername;
command = new System.Data.SqlClient.SqlCommand();
command.CommandText = "Select userName from [User] where userid = #userid";
command.Parameters.AddWithValue("#userid", sId);
command.CommandType = CommandType.Text;
conn.Open();
command.Connection = conn;
//Execute
getusername = command.ExecuteScalar();
//check for null due to non existent value in db and return default empty string
string UserName = getusername == null ? string.Empty : getusername.ToString();
return UserName;
}
catch (Exception ex)
{
throw new Exception("Could not get username", ex);
}
finally
{
conn.Close();
}
}
Slight conjecture: if you check the stack for the exception, it is being thrown then the ADO.NET provider for Oracle is reading the underlying rowset to get the first value.
If there is no row, then there is no value to find.
To handle this case execute for a reader and handle Next() returning false for the case of no match.
I Use it Like This with Microsoft Application Block DLL (Its a help library for DAL operations)
public string getCopay(string PatientID)
{
string sqlStr = "select ISNULL(Copay,'') Copay from Test where patient_id=" + PatientID ;
string strCopay = (string)SqlHelper.ExecuteScalar(CommonCS.ConnectionString, CommandType.Text, sqlStr);
if (String.IsNullOrEmpty(strCopay))
return "";
else
return strCopay ;
}
I have seen in VS2010
string getusername = command.ExecuteScalar();
gives compilation error,
Cannot implicitly convert type object to string.
So you need to write
string getusername = command.ExecuteScalar().ToString();
when there is no record found in database it gives error
Object reference not set to an instance of an object
and when I comment '.ToString()', it is not give any error. So I can say ExecuteScalar not throw an exception. I think anserwer given by #Rune Grimstad is right.
I had this issue when the user connecting to the database had CONNECT permissions, but no permissions to read from the database. In my case, I could not even do something like this:
object userNameObj = command.ExecuteScalar()
Putting this in a try/catch (which you should probably be doing anyway) was the only way I could see to handle the insufficient permission issue.
object objUserName;
objUserName = command.ExecuteScalar();
if (objUserName == null) //if record not found ExecuteScalar returns null
{
return "";
}
else
{
if (objUserName == DBNull.Value) //if record found but value in record field is null
{
return "";
}
else
{
string getusername = objUserName.ToString();
return getusername;
}
}
/* Select some int which does not exist */
int x = ((int)(SQL_Cmd.ExecuteScalar() ?? 0));
I used this in my vb code for the return value of a function:
If obj <> Nothing Then
Return obj.ToString()
Else
Return ""
End If
Try this code, it appears to solve your problem.
Dim MaxID As Integer = Convert.ToInt32(IIf(IsDBNull(cmd.ExecuteScalar()), 1, cmd.ExecuteScalar()))
I'm using Oracle.
If your sql returns numeric value, which is int, you need to use Convert.ToInt32(object). Here is the example below:
public int GetUsersCount(int userId)
{
using (var conn = new OracleConnection(...)){
conn.Open();
using(var command = conn.CreateCommand()){
command.CommandText = "select count(*) from users where userid = :userId";
command.AddParameter(":userId", userId);
var rowCount = command.ExecuteScalar();
return rowCount == null ? 0 : Convert.ToInt32(rowCount);
}
}
}
Try this
sql = "select username from usermst where userid=2"
string getusername = Convert.ToString(command.ExecuteScalar());