Handle null value in Reader

Hi Varius,

Basic engineering rule is start from basic  if you got any problem or issue.

Here also we have to start from basic that is always use Convert.ToString, Convert.Todecimal  this will handle the null value by default.

My Suggetion don't use direct Data reader value, create model,DTO or class and transfer data the required data. This will help you not only use the data but also for further process.

Regards,

Thank you Amit, that has done it!

So the question is how do I add null in the list

private void AddIfNotNull(List list, object value)
{
    if (value != DBNull.Value && value != null && !string.IsNullOrWhiteSpace(value.ToString()))
    {
        list.Add(decimal.Parse(value.ToString()));
    }
    else
    {
        list.Add(null);
    }
}

I tried with adding else condition but doesn't allow null

The reason I want to ignore null values is because I use yValues in a Chart. If I assign 0 to null then the Chart looks like

What I want is for the line to stop where the value is not null i.e August in my chart

Thank you Amit, I tried first solution proposed by you and I have the following error

To handle null values safely, you can use decimal.TryParse instead of decimal.Parse to avoid errors if any of the Result values are null or not in a correct format. Here's how you can modify your code:

while (rdr.Read())
{
    decimal[] yValues =
    {
        TryParseDecimal(rdr["Result1"]),
        TryParseDecimal(rdr["Result2"]),
        TryParseDecimal(rdr["Result3"]),
        TryParseDecimal(rdr["Result4"]),
        TryParseDecimal(rdr["Result5"]),
        TryParseDecimal(rdr["Result6"]),
        TryParseDecimal(rdr["Result7"]),
        TryParseDecimal(rdr["Result8"]),
        TryParseDecimal(rdr["Result9"]),
        TryParseDecimal(rdr["Result10"]),
        TryParseDecimal(rdr["Result11"]),
        TryParseDecimal(rdr["Result12"])
    };
}

private decimal TryParseDecimal(object value)
{
    return decimal.TryParse(value?.ToString(), out var result) ? result : 0m;  // Return 0 or any default value for null or invalid input
}

If you'd like to ignore null values entirely and not add them to the array, you can dynamically build a list of values and only include those that are not null. For example:

while (rdr.Read())
{
    List yValues = new List();

    AddIfNotNull(yValues, rdr["Result1"]);
    AddIfNotNull(yValues, rdr["Result2"]);
    AddIfNotNull(yValues, rdr["Result3"]);
    AddIfNotNull(yValues, rdr["Result4"]);
    AddIfNotNull(yValues, rdr["Result5"]);
    AddIfNotNull(yValues, rdr["Result6"]);
    AddIfNotNull(yValues, rdr["Result7"]);
    AddIfNotNull(yValues, rdr["Result8"]);
    AddIfNotNull(yValues, rdr["Result9"]);
    AddIfNotNull(yValues, rdr["Result10"]);
    AddIfNotNull(yValues, rdr["Result11"]);
    AddIfNotNull(yValues, rdr["Result12"]);
}

private void AddIfNotNull(List list, object value)
{
    if (value != DBNull.Value && value != null && !string.IsNullOrWhiteSpace(value.ToString()))
    {
        list.Add(decimal.Parse(value.ToString()));
    }
}

If a value is null and you want to provide a default value (e.g., 0):

while (rdr.Read())
{
    decimal[] yValues =
    {
        ParseDecimal(rdr["Result1"]),
        ParseDecimal(rdr["Result2"]),
        ParseDecimal(rdr["Result3"]),
        ParseDecimal(rdr["Result4"]),
        ParseDecimal(rdr["Result5"]),
        ParseDecimal(rdr["Result6"]),
        ParseDecimal(rdr["Result7"]),
        ParseDecimal(rdr["Result8"]),
        ParseDecimal(rdr["Result9"]),
        ParseDecimal(rdr["Result10"]),
        ParseDecimal(rdr["Result11"]),
        ParseDecimal(rdr["Result12"])
    };
}

private decimal ParseDecimal(object value)
{
    if (value == DBNull.Value || value == null || string.IsNullOrWhiteSpace(value.ToString()))
    {
        return 0;
    }
    
    return decimal.Parse(value.ToString());
}

Well, I will have null values for sure but I want them handled. I tried with

rdr["Result12"] == DBNull.Value ? default(int) : decimal.Parse(rdr["Result12"].ToString())

and it makes value equal to 0. I rather want to ignore this value, to not be visible in the list if possible not to make it 0

Hi Marius,

Better to check null first before parse. 

List yValues = new List();

while (rdr.Read())
{
    for (int i = 1; i <= 12; i++)
    {
        string columnName = $"Result{i}";
        object result = rdr[columnName];

        // Check for null or DBNull and parse only if valid
        if (result != DBNull.Value && decimal.TryParse(result.ToString(), out decimal value))
        {
            yValues.Add(value);
        }
        else
        {
            yValues.Add(0); // Add default value if null or parsing fails
        }
    }
}