Casting datareader value to a to a Nullable variable

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I'm trying to run the following code but get a conversion error.

How can I rewrite my code to achieve the same ?

C#

boolResult= (bool?)dataReader["BOOL_FLAG"] ?? true;
intResult= (int?)dataReader["INT_VALUE"] ?? 0;

Thanks

Posted 23-Mar-11 8:33am

elad2109

Updated 23-Mar-11 8:43am

Sandeep Mewara

v2

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4 solutions

Solution 1

You can try

C#

bool boolResult= dataReader.GetBoolean(dataReader.GetOrdinal("BOOL_FLAG"));
int intResult= dataReader.GetInt32(dataReader.GetOrdinal("INT_VALUE"));

I hope it will works. Have a look on this Link[^] also

Edit: Modified for independent of column location. See comments.

Posted 23-Mar-11 8:47am

TweakBird

Updated 23-Mar-11 9:32am

v3

Comments

elad2109 23-Mar-11 15:22pm

I don't want depend on coulmn location. This is a bad practice.

TweakBird 23-Mar-11 15:30pm

This not depend on column location.
bool boolResult= dataReader.GetBoolean(dataReader.GetOrdinal("BOOL_FLAG"));
int intResult= dataReader.GetInt32(dataReader.GetOrdinal("INT_VALUE"));

elad2109 23-Mar-11 15:38pm

What happens if the returned value from the dataReader.GetOrdinal("BOOL_FLAG") is a DBnull value ?

TweakBird 23-Mar-11 23:53pm

Simple thing dear, you can apply conditional operator. already Mike given.

Solution 3

C#

bool boolVar = false;
if (!bool.TryParse(dataReader["BOOL_FLAG"], out boolVar))
    throw new Exception("Didn't read a boolean!");

int intVar = int.MinValue;
if (!int.TryParse(dataReader["INT_VALUE"], out intVar))
    throw new Exception("Didn't read a boolean!");

If you need nullable values, you could set them in the if statement like

C#

bool boolVar = false;
bool? finalBool = false;
if (!bool.TryParse(dataReader["BOOL_FLAG"], out boolVar))
    finalBool = null;
else
    finalBool = (bool?) boolVar;

int intVar = int.MinValue;
int? finalInt = int.MinValue
if (!int.TryParse(dataReader["INT_VALUE"], out intVar))
    finalInt = null
else
    finalInt = (int?) intVar;

Hope this helps!

Hogan

Posted 23-Mar-11 8:52am

snorkie

Comments

elad2109 23-Mar-11 15:31pm

The probelm wasn't the casting but catching a null value.

snorkie 24-Mar-11 14:07pm

I agree that the problem is about catching a null value. However, the code I posted will catch a null via the .TryParse method and I understand it to be much safer if other invalid values are passed in. Sorry that you didn't like it! Good luck! --Hogan

elad2109 24-Mar-11 14:19pm

Didn't mean to offend you. I should have used other words. sorry.

snorkie 24-Mar-11 14:29pm

No offense taken. I wanted to clarify my answer.If I'm wrong, then I need to know so I stop making mistakes. This is a great way to validate/refute what I do every day. The .TryParse method has saved me lots of headache for unvalidated input. --Hogan

Solution 4

Check the blog here for a generic extension solution.

Posted 27-Aug-12 20:12pm

Kai Sevelin

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Wendelius · Accepted Answer · 2011-03-23T08:52:00

Solution 2

Values coming from database are not null if the data is null. You should check against System.DBNull.Value. Something like:

boolResult = dataReader["BOOL_FLAG"] == System.DBNull.Value ? null : (bool?)dataReader.GetBoolean(colNumber);

Posted 23-Mar-11 8:52am

Wendelius

Updated 23-Mar-11 9:20am

v2