Re: c# string.IsNullOrEmpty - C# Discussion Boards

31-May-16 6:59

here is my table sql :

user----------term
John..........diligent
Jane..........new

I have a variable : termUser

and I find easily its value by Sql request when the user is saved it in the mysql table and this user see his term on the screen by (due to) the variable : termUser.
I try it by 2 way ( by if condition) and those way are correct results

/* ......... Sql request ... */

string termUser = String.Empty;
string catchTerm = String.Empty;

while (dataMySqlReader.Read())
{
    catchTerm = (string)dataMySqlReader["user"];  

        // here is 1st way : 
        if (catchTerm != null)
        {
            termUser = (string)dataMySqlReader["term"];
        }
        else
        {
            termUser = "callow";

        }

        // et voici 2e version aussi marche 

        if (String.IsNullOrEmpty(catchTerm))
        {
            termUser = "callow";
        }
        else
        {
            termUser = (string)dataMySqlReader["term"];

        }

}

If the user is not in the mysql table, I think that SQL return 'NULL', so in this case, I want to affect this variable (termUser) by 'callow' : It's only for to display on his monitor.
But my code can not affect my variable.

I changed also my condition but I have not success by this :

     if (String.IsNullOrEmpty(catchTerm))
         //...

<pre>
    if (string.IsNullOrEmpty(catchTerm) == true)
    //...
    </pre>

how I can affect my variable termUser by 'callow when the user is not in my table ?

Thanks

Eddy Vluggen31-May-16 19:40

31-May-16 19:40

A "null" value in a database is not the same an empty string; you might want to compare to

<a href="https://msdn.microsoft.com/nl-nl/library/system.dbnull.value%28v=vs.110%29.aspx">DBNull.Value</a>[<a href="https://msdn.microsoft.com/nl-nl/library/system.dbnull.value%28v=vs.110%29.aspx" target="_blank" title="New Window">^</a>]

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Bernhard Hiller31-May-16 23:55

Bernhard Hiller

31-May-16 23:55

Eddy Vluggen wrote:
A "null" value in a database is not the same an empty string

You haven't ever worked with an Oracle DB, have you? Big Grin | :-D

Eddy Vluggen1-Jun-16 0:04

1-Jun-16 0:04

Aw, I did, but it has been a while since Oracle 7 and selecting from 'dual' Smile | :)

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V.1-Jun-16 1:19

1-Jun-16 1:19

I believe this works in Oracle too?
Confused | :confused:

If issues, please explain, you made me curious... $Shucks | :-\$

(MQOTD rules and previous solutions)

Bernhard Hiller1-Jun-16 4:07

Bernhard Hiller

1-Jun-16 4:07

Well, look at it from a different perspective. Imagine a questionnaire. Someone left a free-text field empty. Does that translate to a null value or string.Empty? Hence an empty string and a null string are the same in an Oracle database. If there's a "not null" constraint on the text field, you cannot insert an empty string either.
At first, I thought that's a WTF. But now I think they got it right.

V.31-May-16 20:09

31-May-16 20:09

As Eddy Vluggen mentioned:

if(dataMySqlReader["user"] != DBNull.Value){
//do this
}
else{
//do that
}

hope this helps.

(MQOTD rules and previous solutions)

modified 1-Jun-16 7:32am.

Richard Deeming1-Jun-16 1:30

Richard Deeming

1-Jun-16 1:30

Won't that produce an InvalidCastException if the field is null?

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- Homer

V.1-Jun-16 1:32

1-Jun-16 1:32

Oops, my copy/paste error ... D'Oh! | :doh:

I'll fix that...

(MQOTD rules and previous solutions)

aspkiddy1-Jun-16 2:50

1-Jun-16 2:50

Thanks but it does not work

Eddy Vluggen1-Jun-16 2:52

1-Jun-16 2:52

What does "not work" mean exactly?

Did it throw an error? If yes, what was the message?

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aspkiddy1-Jun-16 3:05

1-Jun-16 3:05

my variable can not affected

Eddy Vluggen1-Jun-16 5:00

1-Jun-16 5:00

Show us some updated code, maybe we could talk about it Smile | :)

Bastard Programmer from Hell Suspicious | :suss:

If you can't read my code, try converting it here[^]

V.1-Jun-16 2:52

1-Jun-16 2:52

What's the error ?

Why doesn't it work?

(MQOTD rules and previous solutions)

aspkiddy1-Jun-16 2:56

1-Jun-16 2:56

But this version works ! Thumbs Up | :thumbsup:

it is very strange Sniff | :^)

/* ......... Sql request ... */

string termUser = String.Empty;
termUser = "callow";   // newwwwwwwww
string catchTerm = String.Empty;

while (dataMySqlReader.Read())
{
    catchTerm = (string)dataMySqlReader["user"];  
        if (catchTerm != null)
        {
            termUser = (string)dataMySqlReader["term"];
        }

}

V.1-Jun-16 3:00

1-Jun-16 3:00

if dataMySqlReader["user"] is null this thing will crash I think...
Note that I updated my previous answer by removing the string cast (that was a copy/paste error)...

also this:

string termUser = String.Empty;
termUser = "callow";   // newwwwwwwww

is useless, use:

string termUser = "callow";

(MQOTD rules and previous solutions)

aspkiddy1-Jun-16 3:08

1-Jun-16 3:08

but
My variable [termUser] is affected by "callow" with this code : Thumbs Up | :thumbsup:

it is very strange Sniff | :^)

/* ......... Sql request ... */

string termUser = String.Empty;
termUser = "callow";   // newwwwwwwww
string catchTerm = String.Empty;

while (dataMySqlReader.Read())
{
    catchTerm = (string)dataMySqlReader["user"];  
        if (catchTerm != null)
        {
            termUser = (string)dataMySqlReader["term"];
        }

}

Matt T Heffron1-Jun-16 9:25

Matt T Heffron

1-Jun-16 9:25

Just an observation:
Unless the SQL query returns exactly one record, the while loop will end up setting catchTerm to the "user" column from the last record returned, and termUser will be the "term" column from the last record where "user" isn't null (or empty).
Is there a reason that the "user" column can't be checked as part of the SQL query?

"Fairy tales do not tell children the dragons exist. Children already know that dragons exist. Fairy tales tell children the dragons can be killed."
- G.K. Chesterton

aspkiddy2-Jun-16 5:12

2-Jun-16 5:12

I think if the record does not exist, C # does not fit into the while loop

Do I Need The Observer Design Pattern In My Situation

Matt T Heffron2-Jun-16 6:20

Matt T Heffron

2-Jun-16 6:20

Yes, but if the SQL query returns more than one record, then the effects I mentioned will happen.
If the SQL query is structured to return only a single record (or none), then there's no issue.

"Fairy tales do not tell children the dragons exist. Children already know that dragons exist. Fairy tales tell children the dragons can be killed."
- G.K. Chesterton

MadDashCoder31-May-16 6:12

MadDashCoder

31-May-16 6:12

Suppose I have a hotel app where users can check to see if there is any vacant rooms in my hotel.

The vacancy status changes as old customers checkout and new ones checkin.

Does this situation require the Observer Design Pattern? Also if this is a WCF REST app, how do I simulate multiple people using this app?

modified 31-May-16 12:19pm.

Re: Do I Need The Observer Design Pattern In My Situation

Eddy Vluggen31-May-16 19:42

Re: Do I Need The Observer Design Pattern In My Situation

31-May-16 19:42

It's not required; you could simply register checkins in a database.

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If you can't read my code, try converting it here[^]

MadDashCoder1-Jun-16 0:51

MadDashCoder

1-Jun-16 0:51

Hi Eddy, thank you so much for sharing your thought on this.

What is the best way to stress test a WCF RESTful service to simulate multiple users accessing my app?

Re: Do I Need The Observer Design Pattern In My Situation

Eddy Vluggen1-Jun-16 0:57