Hi Vibhu,
I think it would be a good idea if you tell us
what the business rule is. You said "But in a business
world a NULL for an int field or an O in the int field may
mean different things." Give us an example and you will
get more help.
Maybe what you should do is:
If Id is null return a value like -32768.
If Name is nulll return a values(string) as (UNKNOW).
Using this technique you now that the Id or Name fields
are null.
Thanks!!
>-----Original Message-----
>I do agree that database null and DbNull are different.
>But in a business world a NULL for an int field or an O
in
>the int field may mean different things.
>I am aware of the boxing feature. It is not useful though
>to just turn an int to an object. Then I have to know
what
>type it is to cast it back
>So i am think of creating owr own types Integer, Float,
>Double and then provide static methods
> public static Integer GetInteger(IDataReader reader,
>string columnName) {
> int value;
> int columnNum = reader.GetOrdinal
>(columnName);
> if(reader.IsDBNull(columnNum)){
> return null;
> }else{
> value =(int)reader[columnName];
> return new Integer(value);
> }
>
> }
>
> public static string GetString(IDataReader
reader,
>string columnName){
> int columnNum = reader.GetOrdinal
>(columnName);
> if(reader.IsDBNull(columnNum)){
> return null;
> }else{
> return (string)reader[columnName];
> }
> }
>>-----Original Message-----
>>null in a database means unknown value, while a null in
>c# or java means
>>unassigned value. there are subtle differences, this is
>why dbnull is not
>>mapped to null.
>>
>>..net value types (unlike java) have no base class. to
>use them as an object
>>(called boxing) you just assign them to the base class
>object, which can
>>hold a reference to any value type.
>>
>> int i = 0;
>> object o = i;
>>
>>you cast to unbox
>>
>> i = (int) o;
>>
>>you can use object to get around the if on the
>datareader, but you will need
>>the if on every reference to the object, as a Db.Null or
>null will not cast
>>to an int. if you just want to cast Db.Null to 0 or "",
>then supplay a
>>static function.
>>
>>static int ToInt(IDataReader dr, string colName)
>>{
>> int columnNum = dr.GetOrdinal(colName);
>> if (dr.IsDBNull(columnNum))
>> return 0;
>> else
>> return dr.GetInt32(columnNum);
>>}
>>
>>
>>
>>
>>"Vibhu Srinivasan" <(E-Mail Removed)> wrote in
>message
>>news:002101c34a23$ca0609d0$(E-Mail Removed)...
>>> I am using data reader for reading tables.
>>> I have some issues with ADO readers, having come from a
>>> java perspective
>>>
>>> When reading a table say Account table ( which has two
>>> fields Id(int), Name(varchar)) both can be null
>>>
>>> In the C# code i end up doing
>>>
>>> int id = (int)reader["Id"];
>>> string name = (string)reader["Name"];
>>>
>>> 1) If the id or name Name is NULL this blows up with a
>ull
>>> pointer . So i have to
>>>
>>> int columnNum =
>>> reader.GetOrdinalcolumnName);
>>>
>>> if(reader.IsDBNull(columnNum)){
>>> then read the column.
>>> }
>>>
>>> This int is a value type , how can i represent a NULL
>>> object in the system. Is there a equivalent int object(
>>> something like the Integer class in java to represent a
>>> NULL value.
>>>
>>> 2) Is there a way to set up reader to retutn a DBNull
>>> object if there are null values in the database.
>>> What i ideally want to do is
>>> reader.GetInteger("ColumnName"){
>>>
>>> }
>>> that returns a Integer and similarly reader.SetInteger
>>> (Integer){
>>>
>>> }
>>> like i can easily do in the Java world.
>>> Not quite sure why this was left out in .NET
>>>
>>> Appreciate any feedback
>>> Vibhu Srinivasan
>>
>>
>>.
>>
>.
>
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