What is a null value answer?

A null value in a relational database is used when the value in a column is unknown or missing . A null is neither an empty string (for character or datetime data types) nor a zero value (for numeric data types).

Do empty strings take up RAM?

Even a string of length zero can require memory to store it, depending on the format being used . In most programming languages, the empty string is distinct from a null reference (or null pointer) because a null reference points to no string at all, not even the empty string.

What is an example of a NULL value?

A null indicates a lack of a value, which is not the same thing as a zero value. For example, consider the question "How many books does Adam own?" The answer may be "zero" (we know that he owns none) or "null" (we do not know how many he owns) .

What is a NULL answer?

"Null" essentially means that the question has not been answered . " 0" is an. answer, you don't want to confuse the two.

What is the difference between null and empty string?

The Java programming language distinguishes between null and empty strings. An empty string is a string instance of zero length, whereas a null string has no value at all . An empty string is represented as "" . It is a character sequence of zero characters.

Is it better to use string empty?

Use String. Empty when emphasizing clarity and readability in your code .In scenarios where multiple instances of an empty string might be used, String. Empty can lead to better performance due to its one-time initialization.

Why do we use empty strings?

An empty string is useful when the data comes from multiple resources . NULL is used when some fields are optional, and the data is unknown.

What is considered a NULL value?

A NULL value is used to represent a missing value, but it usually has one of three different interpretations: The value unknown (value exists but is not known) Value not available (exists but is purposely withheld) Attribute not applicable (undefined for this tuple)

What is a NULL response?

A null response indicates that there was no successful connection when you attempt to connect to our gateway ."

Is NULL value 1 or 0?

Unlike zero, null values are not an absolute or something quantifiable; they're an unknown . As such they should not be stored as numbers (i.e. 0, -999, 999, etc.).

The answer to that is rather simple: a NULL means that there is no value , we're looking at a blank/empty cell, and 0 means the value itself is 0.

DropDownLists and NULL values

Neil

I'd like to know what the best method is for handling NULL (or 0)
values within a DropDownList.

If a database lookup value is optional I would normally consider
leaving it NULL but this leads to problems with DropDownLists because
there is no value to bind to and an eror is raised.

I considered a method whereby the DropDownList has a an index value of
0 inserted with a space character as the text after it has retrieved
the data from the source table. As it has a 0 index value it would
appear at the top of the list and would indicate that no selection had
been made. Within the database the column would be defined with a
default value of 0. Thus the 0 value retrieved from the db would bind
to the 0 value inserted into the DropDownList.

I've tried to get this approach to work but the code always errors
because there is no value to bind the retrieved db value against. I've
obviously not got the 0 value insertion code in the right place.

The web form is filling a formview control via a sqldatasource
following the selection of a record on a gridview.
Can someone point me in the right direction as to how such optional
lookup data in a dropdownlist should be handled

Jan 30 '06 #1

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Neil,
Try posting some snippet code i'm sure it would help people here to
help you.
What you can do is don't let your selected value go to the DB unless
some option value has been selected.
use ddl.selectedind ex(this gives you the index of the DropDownList)
Hope that helps
Patrick

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Jan 30 '06 #2

Wiktor Zychla [C# MVP]

> I'd like to know what the best method is for handling NULL (or 0)

values within a DropDownList.

I also had this problem when binding to an object layer (ObjectDataSour ce).
my solution is as follows:

1) in the OnDataBound event of the dropdown I call a method that inserts an
element to the top of the list (["empty", "empty"])

2) I set the SelectedValue:

SelectedValue=' <%# Eval("expressio n")!=null ? Eval("expressio n").ToString ()
: null %>'>

note that when null is used as the SelectedValue, the top most element will
be choosen (in this case it is the ["empty", "empty"] element.

3) I read the SelectedValue:

string v_exp = DropDown.Select edValue;
int? id = v_exp == "empty" ? new Nullable<int>() : int.Parse( v_exp );

Regards,

Wiktor Zychla

Jan 30 '06 #3

Neil

>What you can do is don't let your selected value go to the DB unless

some option value has been selected.

Is it possible to do this when using a sqldatasource with a formview?
Wouldn't this approach mean that you'd have to change the update
statement assigned to the sqldatasource to remove the value of any
columns fed by a dropdownlist that hadn't been selected?

Rather than looking for a specific code resolution I was interested
more in the approach I should be taking based upon other's practices.
After all, this must be a common issue that developers handle.

Jan 30 '06 #4

Sinu

The best way is to test this way If(!object.Equa ls("obj1", null));
This gives the perfect ans. Any doubts then pls contact MICROSOFT!
--
Shrinivas Reddy.
Systems Analyst
Satyam Computer Services Ltd.
"Wiktor Zychla [C# MVP]" wrote:

I'd like to know what the best method is for handling NULL (or 0)
values within a DropDownList.
I also had this problem when binding to an object layer (ObjectDataSour ce).
my solution is as follows:
1) in the OnDataBound event of the dropdown I call a method that inserts an
element to the top of the list (["empty", "empty"])
2) I set the SelectedValue:
SelectedValue=' <%# Eval("expressio n")!=null ? Eval("expressio n").ToString ()
: null %>'>
note that when null is used as the SelectedValue, the top most element will
be choosen (in this case it is the ["empty", "empty"] element.
3) I read the SelectedValue:
string v_exp = DropDown.Select edValue;
int? id = v_exp == "empty" ? new Nullable<int>() : int.Parse( v_exp );
Regards,
Wiktor Zychla

Jan 30 '06 #5

sloan

I usually do a
ddlMyDDL.Items. insert(0 , new ListItem(0 , "--Select--"))

I'm going from memory, but what I mean is a new ListItem with the value of
0, text of "--Select--", and I use the Items.Insert (at position 0)
(which I do immediately AFTER the DataBind() method)

That may not be what you mean...as in..if the value coming from the DB is
null to begin with or something.

...

But what I propose will put that "fake" value in there.

If my database doesn't actually like a zero, in my businesslayer, I will
convert a 0 to DBNULL ...

...
Ok, I just did a quick google, and found this:
http://www.4guysfromrolla.com/webtech/073101-1.shtml

(They don't do the explicit ListItem.Value of 0 like I did, but its the same
concept)

"Neil" <ne*********@sy napse-partnership.com > wrote in message
news:11******** **************@ o13g2000cwo.goo glegroups.com.. .

I'd like to know what the best method is for handling NULL (or 0)
values within a DropDownList.
If a database lookup value is optional I would normally consider
leaving it NULL but this leads to problems with DropDownLists because
there is no value to bind to and an eror is raised.
I considered a method whereby the DropDownList has a an index value of
0 inserted with a space character as the text after it has retrieved
the data from the source table. As it has a 0 index value it would
appear at the top of the list and would indicate that no selection had
been made. Within the database the column would be defined with a
default value of 0. Thus the 0 value retrieved from the db would bind
to the 0 value inserted into the DropDownList.
I've tried to get this approach to work but the code always errors
because there is no value to bind the retrieved db value against. I've
obviously not got the 0 value insertion code in the right place.
The web form is filling a formview control via a sqldatasource
following the selection of a record on a gridview.
Can someone point me in the right direction as to how such optional
lookup data in a dropdownlist should be handled

Jan 31 '06 #6

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