Small c# challenge [modified]

[Ennis Ray Lynch Jr]

you could also rewrite the query

SELECT
isnul(foo, '')
FROM
wherever

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[cpkilekofp]

Marc Clifton wrote:

And yeah, you can really get rid of the if this way: object Foo;...temp.Foo=rd[0];

That's what I would have thought from the C# 2.0 spec. But I have to ask: have you tried it, and observed it to work?

[cpkilekofp]

Ennis Ray Lynch, Jr. wrote:

you could also rewrite the query SELECT isnul(foo, '')FROM wherever

Oh, yes, I ALWAYS want a VARCHAR(0) returned when I'm expecting a double :laugh:

[Ennis Ray Lynch Jr]

I wasn't paying any attention. I just squeezed in an emergency production db fix using that exact code so I naturally used the ''.

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[James Simpson]

You could also write a set of extension methods for DbDataReader eg public static double? GetDoubleOrDefault(this DbDataReader src, int index) { return GetDoubleOrDefault(src, index, 0); } public static double? GetDoubleOrDefault(this DbDataReader src, int index, double? def) { return this.IsDbNull(index) == true ? def : this.GetDouble(index) } then your example might be: temp.Foo = rd.GetDoubleOrDefault(0); or temp.Foo = rd.GetDoubleOrDefault(0, 0);

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[Simon P Stevens]

I like that. Keeps the code nice and readable.

Simon

[PIEBALDconsult]

I wouldn't use the tertiary operator in this case either, most times I use it to avoid a local variable: System.Console.Writeline ( rd [ 0 ] == System.DBNull.Value ? "null" : rd [ 0 ].ToString() ) ; In this case I'd initialize Foo to null in the class (shouldn't it be anyway?) and then:

if ( rd [ 0 ] != System.DBNull.Value )
{
temp.Foo = (double) rd [ 0 ] ;
}

But this kind of stuff belongs encapsulated in something, perhaps pass the DataReader to the constructor of myClass and hide the details there. This is why my wrapper for ExecuteScalar requires the user to pass in a value to use in case of null.

    public virtual T
    ExecuteScalar<T>
    (
        T IfNull
    )
    {
        lock ( this.cmd )
        {
            **T    result    = IfNull ;**
            bool wasclosed = this.IsClosed ;
            
            try
            {
                object temp ;
                
                if ( wasclosed )
                {
                    this.Open() ;
                }

                temp = this.cmd.ExecuteScalar() ;

                **if ( ( temp != null ) && ( temp != System.DBNull.Value ) )
                {
                    result = (T) temp ;
                }**
            }
            catch ( System.Exception err )
            {
                throw ( WrapDataException ( "ExecuteScalar" , this.cmd , err ) ) ;
            }
            finally
            {
                if ( wasclosed )
                {
                    this.Close() ;
                }
            }

            return ( result ) ;
        }
    }

[Giorgi Dalakishvili]

rd[0] returns object, not double.

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[Giorgi Dalakishvili]

In that case how will you know if the database contained zero or it was null and isnull turned it into zero?

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[Ennis Ray Lynch Jr]

That is why I usually use the ternary operator. However, if you are using .NET 1.0 or 1.1 my solution is valid for your question.

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[Giorgi Dalakishvili]

What if you have several properties in your class? Code will get very ugly.

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[Giorgi Dalakishvili]

Type of conditional expression cannot be determined because there is no implicit conversion between '<null>' and 'double' Giorgi Dalakishvili #region signature My Articles / My Latest Article[^] / My blog[^] #endregion

modified on Thursday, October 23, 2008 11:33 AM

[Ennis Ray Lynch Jr]

Follow the subthread I have already responded to this, it was a mistake on my part and should have been isnull(foo, 0) or more fully isnull(foo, cast(0 as float))

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[Giorgi Dalakishvili]

Sorry, some characters got swallowed. The code will not compile.

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[Chris Losinger]

1. initialize temp's properties to null 2. try { do all your Get*() calls } or, write Get*Default functions which do the null test and assign either the recordset value, or a default value in case the field is null.

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[Ennis Ray Lynch Jr]

Ah, yeah, sometimes the ternary is a bear because of the typing. Cast using (double?) instead I believe. Really, however, if this is to migrate into a programming question it should not be in the lounge. The logic is inferrable from what I wrote.

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[Giorgi Dalakishvili]

Nice solution. My solution is similar but a little bit different.

Ennis Ray Lynch, Jr. wrote:

Really, however, if this is to migrate into a programming question it should not be in the lounge.

I don't think it's a programming question as I already had solution when I posted it.

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[cpkilekofp]

;-) Happens to the best of us, and even me occasionally :laugh:

[Marc Clifton]

cpkilekofp wrote:

But I have to ask: have you tried it, and observed it to work?

It works because all the fields are objects, unless you use a typed data reader. Marc

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[Marc Clifton]

Giorgi Dalakishvili wrote:

rd[0] returns object, not double.

Yes, I know. What did you mean? I was being flippant, because you obviously have to deal with converting the object to a double at some point. But it was a way to get rid of the "if". Marc

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