Reader with access database

abed akhi

14y2.4k.NET

Hi,

I just want to know if my information are correct:

the reader with the sql or.. database can always access the reader.read() method but if there is no data found it retrieves 0 or null as result,

but with the access database if there is no data then the reader.read() is false and does not access the content written in reader.read()

which means in sql when I put
reader.read(){
//write a code

}

the reader accesses the code but retrieves null result if no data found but with the access database the reader does not even access the code if no data found right?

6 Replies

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Vulpes14y ago
Accepted answer
AFAIK, the Read() method of all the .NET data readers (SqlDataReader, OleDbDataReader, OdbcDataReader etc) behaves the same.

It attempts to advance to the next record and, if there is one, returns true. Otherwise, when there are no more records to read, it returns false.

It follows that you can only access the record if the Reader() method returns true.

Initially, it's set at a position just before the first record and so needs to be called before the first record can be accessed.
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abed akhi14y ago
No what I was doing is that I was adding:
int id=0;

and then the while (reader.read()){id=Int32.parse(reader[0].tostring)} and then if id!=0 do something, :) I think that because I did it since too long my ideas are jumbled thanks again you're right.
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Vulpes14y ago
There is actually a record there and the value of its first column (the column with an index of 0) happens to be 0.

If that's an Id column, then I don't know how the existence of such a record could come about without knowing the structure of the database and the query used to build the record-set.
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abed akhi14y ago
but I used sql database before with asp.net and when I placed

sqlcommand s=new sqlcommand("Select id from table where username=etc");

while (reader.read())
{
id=Int32.Parse(reader[0].tostring());

}

I had an id=0 althought there wasn't any username that is called etc...

so it entered the .read() method even if it's false..

Or am I missing something here?
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Vulpes14y ago
The .NET DataReader.Read() returns false when there are no more records to read.

I think you may be confusing the situation with similar functions in other languages (such as C) which typically return 0 if there are no more records.

In C#, there are no conversions defined between the int and bool types even though bools are represented by single bytes with values of 0 (for false) or 1 (for true).
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abed akhi14y ago
thanks, but I think that with a sql database the reader do access the while(reader.read) even if there is no data and returns the value of 0 cz I already worked on sql databases..
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