String and null vs DBNULL

  • Thread starter Thread starter tshad
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T

tshad

I have a function that is being passed as an object but is really a string
so that I can handle DBNull.Value.

You cannot pass a DBNull.Value to a string parameter but you can pass a null
value. Not sure why this is but if I have the following:

private static void SetAddressFields(Address adress, object zip)

where Address is class which has a string property of zip (address.Zip).

In the routing I have the following code:

if (zip != DBNull.Value)
address.Zip = (string)zip;
else
address.FieldToNull("Zip");

Where address.FieldToNull handles null entries.

What is confusing is that if I do:

SetAddressFields(address, dr["Zip"]);

And dr["Zip"] is equal to DBNull.Zip,

my test works: if (zip != DBNull.Value).

If I call the same function where I pass a null where zip is equal to null:

SetAddressFields(address, zip)

or

SetAddressFields(address, null);

Both of these pass back a false from the DBNull.Value test because null is
not DBNull.Value test.

But the code still works.

You can set a string to null, but not to DBNull.Value.

I thought that I would have to change the code to:

if (zip != DBNull.Value && zip != null)

To handle both situations but since you can set a string to null, you only
have to handle the DBNull situation.

Is there another way to handle both situations?

Thanks,

Tom
 
Perhaps.

Have you looked at this?

if (String.IsNullOrEmpty(zip) == false)
{
// your code here
}
 
....also, System.DbNull is a class, so the types are not the same. Meaning,
you'd have to cast your object to the appropriate type, but once you cast it
to a DbNull, I'm betting there's no reason to test to see if it is DbNull,
right?
 
jp2msft said:
Perhaps.

Have you looked at this?

if (String.IsNullOrEmpty(zip) == false)
{
// your code here
}
Click to expand...
But would String.IsNullOrEmpty handle both "null" and DBNull.Value?

Thanks,

Tom
tshad said:
I have a function that is being passed as an object but is really a
string
so that I can handle DBNull.Value.

You cannot pass a DBNull.Value to a string parameter but you can pass a
null
value. Not sure why this is but if I have the following:

private static void SetAddressFields(Address adress, object zip)

where Address is class which has a string property of zip (address.Zip).

In the routing I have the following code:

if (zip != DBNull.Value)
address.Zip = (string)zip;
else
address.FieldToNull("Zip");

Where address.FieldToNull handles null entries.

What is confusing is that if I do:

SetAddressFields(address, dr["Zip"]);

And dr["Zip"] is equal to DBNull.Zip,

my test works: if (zip != DBNull.Value).

If I call the same function where I pass a null where zip is equal to
null:

SetAddressFields(address, zip)

or

SetAddressFields(address, null);

Both of these pass back a false from the DBNull.Value test because null
is
not DBNull.Value test.

But the code still works.

You can set a string to null, but not to DBNull.Value.

I thought that I would have to change the code to:

if (zip != DBNull.Value && zip != null)

To handle both situations but since you can set a string to null, you
only
have to handle the DBNull situation.

Is there another way to handle both situations?

Thanks,

Tom
Click to expand...
Click to expand...
 
No, but...

Again, DbNull is a class that is defined to be null.

I don't understand what you are asking. DbNull does not have a Value property.

Have you created your own DbNull class? If you are using the standard
System.DbNull, it does not have any properties.

Perhaps you could right-click on your DbNull and click Go To Definition to
help me better understand your question.

tshad said:
jp2msft said:
Perhaps.

Have you looked at this?

if (String.IsNullOrEmpty(zip) == false)
{
// your code here
}
Click to expand...
But would String.IsNullOrEmpty handle both "null" and DBNull.Value?

Thanks,

Tom
tshad said:
I have a function that is being passed as an object but is really a
string
so that I can handle DBNull.Value.

You cannot pass a DBNull.Value to a string parameter but you can pass a
null
value. Not sure why this is but if I have the following:

private static void SetAddressFields(Address adress, object zip)

where Address is class which has a string property of zip (address.Zip).

In the routing I have the following code:

if (zip != DBNull.Value)
address.Zip = (string)zip;
else
address.FieldToNull("Zip");

Where address.FieldToNull handles null entries.

What is confusing is that if I do:

SetAddressFields(address, dr["Zip"]);

And dr["Zip"] is equal to DBNull.Zip,

my test works: if (zip != DBNull.Value).

If I call the same function where I pass a null where zip is equal to
null:

SetAddressFields(address, zip)

or

SetAddressFields(address, null);

Both of these pass back a false from the DBNull.Value test because null
is
not DBNull.Value test.

But the code still works.

You can set a string to null, but not to DBNull.Value.

I thought that I would have to change the code to:

if (zip != DBNull.Value && zip != null)

To handle both situations but since you can set a string to null, you
only
have to handle the DBNull situation.

Is there another way to handle both situations?

Thanks,

Tom
Click to expand...
Click to expand...
Click to expand...
 
jp2msft said:
No, but...

Again, DbNull is a class that is defined to be null.

I don't understand what you are asking. DbNull does not have a Value
property.

Have you created your own DbNull class? If you are using the standard
System.DbNull, it does not have any properties.

Perhaps you could right-click on your DbNull and click Go To Definition to
help me better understand your question.
Click to expand...


Actually, the class DBNull has a static field called Value.

A way to use it is shown in MSDN at
http://msdn.microsoft.com/en-us/library/system.dbnull.value.aspx.
 
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