CODEWITHSUNDEEP
c#dbnull
Thomas
Thomas

Reputation: 6670

DBNull From DataSet Cast to Nullable Constructor

I have a constructor with a signature that looks something like:

public Something(UInt64 uid, UInt64? parentUniqueId)
{
    // ...
}

The constructor is called with the result of a database retrieval. It is possible that the parentUniqueId returns as DBNull.

Currently, the calling code looks something like:

var s = new Something(uid: Convert.ToUint64(row[0]), ConvertTo.Unit64(row[1]))

That doesn't work, so I tried (in the second cast) to do (Unit64?)row[1]; but, that is freaking out.

The challenge here is that Something is a base class that accepts "specified" arguments, e.g. Unit64 and it is being called from an inheriting class that accepts a DataRow. So, you can imagine:

public SomethingSpecific(DataRow row)
    : base(
        uid: Convert.ToUInt64(row[0]))
        // etc...
     )
{ }

Is this possible in one line? How would I handle the DBNull conversion?

Upvotes: 1

Views: 137

Answers (2)

NineBerry
NineBerry

Reputation: 28499

Write your own convert method like this:

public static class MyConvert
{
    public static UInt64? ToUInt64OrNull(object value)
    {
        if(Convert.IsDBNull(value) || value == null)
        {
            return null;
        }
        else
        {
            return Convert.ToUInt64(value);
        }

    }
}

null and DBNull are two very different values. So you have to explicitly handle them both.

Then use it like this:

var s = new Something(uid: Convert.ToUInt64(row[0]), MyConvert.ToUInt64OrNull(row[1]))

It is assumed that row[0] will never be null or DBNull, but that row[1] can be DBNull and will be passed as null to the constructor then.

This is how you would use it when writing your child class:

public SomethingSpecific(DataRow row)
    : base(
        uid: Convert.ToUInt64(row[0]),
        parentUniqueId: MyConvert.ToUInt64OrNull(row[1])
        // etc...
     )
{ }

Upvotes: 3

DHN
DHN

Reputation: 4865

How about a bit more defensive programming? E.g.

var s = new Something(uid: row[0] != null ? Convert.ToUInt64(row[0]) : default(UInt64), parentUniqueId: row[1] != null ? Convert.ToUInt64(row[1]) : default(UInt64?));

It's not nice but it would do the trick.

Upvotes: 1

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