Assign null to a SqlParameter

问题

The following code gives an error - \"No implicit conversion from DBnull to int.\"

SqlParameter[] parameters = new SqlParameter[1];    
SqlParameter planIndexParameter = new SqlParameter(\"@AgeIndex\", SqlDbType.Int);
planIndexParameter.Value = (AgeItem.AgeIndex== null) ? DBNull.Value : AgeItem.AgeIndex;
parameters[0] = planIndexParameter;

回答1:

The problem is that the ?: operator cannot determine the return type because you are either returning an int value or a DBNull type value, which are not compatible.

You can of course cast the instance of AgeIndex to be type object which would satisfy the ?: requirement.

You can use the ?? null-coalescing operator as follows

SqlParameter[] parameters = new SqlParameter[1];     
SqlParameter planIndexParameter = new SqlParameter("@AgeIndex", SqlDbType.Int);
planIndexParameter.Value = (object)AgeItem.AgeIndex ?? DBNull.Value;
parameters[0] = planIndexParameter;

Here is a quote from the MSDN documentation for the ?: operator that explains the problem

Either the type of first_expression and second_expression must be the same, or an implicit conversion must exist from one type to the other.

回答2:

The accepted answer suggests making use of a cast. However, most of the SQL types have a special Null field which can be used to avoid this cast.

For example, SqlInt32.Null "Represents a DBNull that can be assigned to this instance of the SqlInt32 class."

int? example = null;
object exampleCast = (object) example ?? DBNull.Value;
object exampleNoCast = example ?? SqlInt32.Null;

回答3:

You need pass DBNull.Value as a null parameter within SQLCommand, unless a default value is specified within stored procedure (if you are using stored procedure). The best approach is to assign DBNull.Value for any missing parameter before query execution, and following foreach will do the job.

foreach (SqlParameter parameter in sqlCmd.Parameters)
{
    if (parameter.Value == null)
    {
        parameter.Value = DBNull.Value;
    }
}

Otherwise change this line:

planIndexParameter.Value = (AgeItem.AgeIndex== null) ? DBNull.Value : AgeItem.AgeIndex;

As follows:

if (AgeItem.AgeIndex== null)
    planIndexParameter.Value = DBNull.Value;
else
    planIndexParameter.Value = AgeItem.AgeIndex;

Because you can't use different type of values in conditional statement, as DBNull and int are different from each other. Hope this will help.

回答4:

With one line of code, try this:

var piParameter = new SqlParameter("@AgeIndex", AgeItem.AgeIndex ?? (object)DBNull.Value);

回答5:

Try this:

SqlParameter[] parameters = new SqlParameter[1];    
SqlParameter planIndexParameter = new SqlParameter("@AgeIndex", SqlDbType.Int);

planIndexParameter.IsNullable = true; // Add this line

planIndexParameter.Value = (AgeItem.AgeIndex== null) ? DBNull.Value : AgeItem.AgeIndex== ;
parameters[0] = planIndexParameter;

回答6:

If you use the conditional(ternary) operator the compiler needs an implicit conversion between both types, otherwise you get an exception.

So you could fix it by casting one of both to System.Object:

planIndexParameter.Value = (AgeItem.AgeIndex== null) ? DBNull.Value : (object) AgeItem.AgeIndex;

But since the result is not really pretty and you always have to remember this casting, you could use such an extension method instead:

public static object GetDBNullOrValue<T>(this T val)
{
    bool isDbNull = true;
    Type t = typeof(T);

    if (Nullable.GetUnderlyingType(t) != null)
        isDbNull = EqualityComparer<T>.Default.Equals(default(T), val);
    else if (t.IsValueType)
        isDbNull = false;
    else
        isDbNull = val == null;

    return isDbNull ? DBNull.Value : (object) val;
}

Then you can use this concise code:

planIndexParameter.Value = AgeItem.AgeIndex.GetDBNullOrValue();

回答7:

In my opinion the better way is to do this with the Parameters property of the SqlCommand class:

public static void AddCommandParameter(SqlCommand myCommand)
{
    myCommand.Parameters.AddWithValue(
        "@AgeIndex",
        (AgeItem.AgeIndex== null) ? DBNull.Value : AgeItem.AgeIndex);
}

回答8:

Consider using the Nullable(T) structure available. It'll let you only set values if you have them, and your SQL Command objects will recognize the nullable value and process accordingly with no hassle on your end.

回答9:

Try this:

if (AgeItem.AgeIndex != null)
{
   SqlParameter[] parameters = new SqlParameter[1];
   SqlParameter planIndexParameter = new SqlParameter("@AgeIndex", SqlDbType.Int);
   planIndexParameter.Value = AgeItem.AgeIndex;
   parameters[0] = planIndexParameter;
}

In other words, if the parameter is null just don't send it to your stored proc (assuming, of course, that the stored proc accepts null parameters which is implicit in your question).

回答10:

try something like this:

if (_id_categoria_padre > 0)
{
    objComando.Parameters.Add("id_categoria_padre", SqlDbType.Int).Value = _id_categoria_padre;
}
else
{
    objComando.Parameters.Add("id_categoria_padre", DBNull.Value).Value = DBNull.Value;
}

回答11:

int? nullableValue = null;
object nullableValueDB
{
   get{
       if(nullableValue==null)
          return DBNull.Value;
       else
          return (int)nullableValue;
   }
}

I'm solving like that.

回答12:

if (_id_categoria_padre > 0)
{
    objComando.Parameters.Add("id_categoria_padre", SqlDbType.Int).Value = _id_categoria_padre;
}
else
{
    objComando.Parameters.Add("id_categoria_padre", DBNull.Value).Value = DBNull.Value;
}

回答13:

if (AgeItem.AgeIndex== null)  
    cmd.Parameters.Add(new SqlParameter("ParaMeterName", SqlDbType.DateTime).Value = DBNull);  
else  
    cmd.Parameters.Add(new SqlParameter("ParaMeterName", SqlDbType.DateTime).Value = AgeItem.AgeIndex);

回答14:

This is what I simply do...

        var PhoneParam = new SqlParameter("@Phone", DBNull.Value);
        if (user.User_Info_Phone != null)
        {
            PhoneParam.SqlValue = user.User_Info_Phone;
        }

        return this.Database.SqlQuery<CustLogonDM>("UpdateUserInfo @UserName, @NameLast, @NameMiddle, @NameFirst, @Address, @City, @State, @PostalCode, @Phone",
            UserNameParam, NameLastParam, NameMiddleParam, NameFirstParam, AddressParam, CityParam, StateParam, PostalParam, PhoneParam).Single();

回答15:

            dynamic psd = DBNull.Value;

            if (schedule.pushScheduleDate > DateTime.MinValue)
            {
                psd = schedule.pushScheduleDate;
            }


            sql.DBController.RunGeneralStoredProcedureNonQuery("SchedulePush",
                     new string[] { "@PushScheduleDate"},
                     new object[] { psd }, 10, "PushCenter");

回答16:

A simple extension method for this would be:

    public static void AddParameter(this SqlCommand sqlCommand, string parameterName, 
        SqlDbType sqlDbType, object item)
    {
        sqlCommand.Parameters.Add(parameterName, sqlDbType).Value = item ?? DBNull.Value;
    }

回答17:

I use a simple method with a null check.

    public SqlParameter GetNullableParameter(string parameterName, object value)
    {
        if (value != null)
        {
            return new SqlParameter(parameterName, value);
        }
        else
        {
            return new SqlParameter(parameterName, DBNull.Value);
        }
    }

回答18:

My code, working in real project Look the ternary operator beafore make the sqlparameter this is the best way for me, withou problems:

    public bool Key_AddExisting
    (
          string clave
        , int? idHito_FileServer
        , int? idTipoDocumental_Almacen
        , string tipoExp_CHJ
        , int idTipoExp_Verti2
        , int idMov_Verti2
    )
    {
        List<SqlParameter> pars = new List<SqlParameter>()
        {
              new SqlParameter { ParameterName = "@Clave", Value = clave }
    LOOK -> , idHito_FileServer == null ? new SqlParameter { ParameterName = "@IdHito_FileServer", Value = DBNull.Value } : new SqlParameter { ParameterName = "@IdHito_FileServer", Value = idHito_FileServer }
    LOOK -> , idTipoDocumental_Almacen == null ? new SqlParameter { ParameterName = "@IdTipoDocumental_Almacen", Value = DBNull.Value } : new SqlParameter { ParameterName = "@IdTipoDocumental_Almacen", Value = idTipoDocumental_Almacen }
            , new SqlParameter { ParameterName = "@TipoExp_CHJ", Value = tipoExp_CHJ }
            , new SqlParameter { ParameterName = "@IdTipoExp_Verti2", Value = idTipoExp_Verti2 }
            , new SqlParameter { ParameterName = "@IdMov_Verti2", Value = idMov_Verti2 }
        };

        string sql = "INSERT INTO [dbo].[Enlaces_ClavesCHJ_MovimientosVerti2] " +
            "( " +
            "  [Clave] " +
            ", [IdHito_FileServer] " +
            ", [IdTipoDocumental_Almacen] " +
            ", [TipoExp_CHJ] " +
            ", [IdTipoExp_Verti2] " +
            ", [IdMov_Verti2] " +
            ") " +
            "VALUES" +
            "( " +
            "  @Clave" +
            ", @IdHito_FileServer" +
            ", @IdTipoDocumental_Almacen" +
            ", @TipoExp_CHJ" +
            ", @IdTipoExp_Verti2" +
            ", @IdMov_Verti2" +
            ")";

        return DbBasic.ExecNonQuery(ref this.conn, sql, pars);
    }

来源：https://stackoverflow.com/questions/4555935/assign-null-to-a-sqlparameter

标签

dbnull

sqlparameter