IDataReader , SqlDataReader difference

Question

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MIDL

using (IDataReader reader = cmd.ExecuteReader())
        {
            while (reader.Read())
            {
                // get data from the reader
            }
        }

MIDL

using (SqlDataReader reader = cmd.ExecuteReader())
        {
            while (reader.Read())
            {
                // get data from the reader
            }
        }

Hi,

Can someone tell me the difference between these two pieces of code ? Why use IDataReader ?

Posted 26-May-11 0:29am

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parmar_punit 26-May-11 10:02am

Kindly see my new solution...... :)

4 solutions

Solution 4

IDataReader is the generic interface that all data readers implement (including SqlDataReader). There is not much difference in your codes except that using the base interfaces allow you to change the database provider easily without any code change (like switching over from SQL Server to Oracle).

Posted 26-May-11 5:07am

Shameel

Solution 3

This is second time, i'm submitting my Solution....
this time i'm not updating the solution, but put a different solution here......

There is not any difference between using that two different code....
if you are familiar with the Fundamental of C++ then you should know about it that Base type (pointer variable) can refereed to its derived type object...
Here, IDataReader is a base type of DataReader class so it can easily point out to its derived class object...

Thanks & Regards
Punit Parmar

Posted 26-May-11 4:03am

parmar_punit

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parmar_punit · Accepted Answer · 2011-05-26T00:47:00

Solution 2

IDataReader is an InterFace while SqlDataReader is class.... you can see it in the Object browser if you have Visual Studio....
for more details visit...
Link1[^]
Link2[^]

Posted 26-May-11 0:47am

parmar_punit

shanmugam_13 · Accepted Answer · 2011-05-26T00:40:00

Solution 1

SqlDataReader is For only Sql Server where as ,IdataReader is used for all the Relational databases.

Posted 26-May-11 0:40am

shanmugam_13

Comments

Close Network 26-May-11 6:46am

Then, I have a new question. Interface does not hold any definition. Interface can not be instantiated. How can this code be valid ?

IDataReader reader = cmd.ExecuteReader()

cmdExecuteReader returns an object with a value in memory. reader is interface. How can an object be assigned to an interface ? isnt interface just a contract with not method definitions inside ?

Sergey Alexandrovich Kryukov 19-Sep-11 18:37pm

Your understanding of interfaces it totally incorrect. Think about what you say -- if what you think was true, interfaces would be completely useless. You need to understand run-time types and compile-time types. In your sample, reader has compile time type of IDataReader, but its run-time type after assignment becomes the type of some concrete implementation class depending on concrete data provider. The goal is working with interface references, not with class references. As run-time types, they are always implementation class references.

Does it makes things more clear to you?
--SA

parmar_punit 26-May-11 9:54am

The reference variable is created at the time you writing IdataReader reader = cmd.ExecuteReader();
It is possible to create a reference variable of Interface but you are not allowed to initiate an object..
and if you know the Fundamental of C++, Base type can refereed to its derived type...
here IDataReader is a base type of DataReader so it can easily point out to its derived class object...
Thanks & Regards,
Punit Parmar

Sergey Alexandrovich Kryukov 19-Sep-11 18:38pm

Correct. I tried to explain it in some different way above, please see.
--SA