Why datareader is forward only

Alok Pandey

15y10.2kLearn iOS Programming

Hi,

Why datareader is forward only?

Thanks, in advance

10 Replies

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Sam Hobbs15y ago
Performance. I think that one word is sufficient to explain why. If you only need forward-only access, then it is innefficient to do anything more than what forward-only requires. If you need to go backward or anything such as that, then there are other classes and such that can be used.

If the only requirement is to be able to access the previous record, then the code to retain the previous record is trivial.
Manikavelu Velayutham15y ago
I can simply consolidate the answer as below.
- ForwardOnly Resultsets provides better throughput.
- It uses less client and server resources.
- No need to maintain the current record position with respect to the records in the server.
- Data is read as stream and the records can be processed one by one.
- No Caching in the Data Access Layer.
- Forward only Result sets are suitable for reporting and data processing applications where the same operations is performed on the fetched records.
Vulpes15y ago
The problem with reverse traversal of any stream is that, in order to be sure that it will always work, you have to buffer all of the data. As the amount of data to be read from the stream could be huge, this would not be memory efficient and might even be out of the question.

Consequently, all the .NET stream readers I can think of (text, XML, data) are forward only and, if you need reverse traversal, you should cache the rows already read yourself or use a different approach.
Prabhu Raja15y ago
DataReader is a light weight component from microsoft. DataReader is same like as foreach loop, Forward and Read Only.

Why DataReader is Forward Only, the Answer is simple, To increase Performance Because i already described that DataReader is Light-weight Component. The Execution time is slow then work with Datasets. If we need Both Back and Forword Options, We may try with DataTables.

Dataset is an heavy-weight Component, But we Can use Dataset as DataSource But not DataReader as DataSource.
Manikavelu Velayutham15y ago
DataReader is Forward Only. Actual question is why the DataReader is Forward Only ?

Some said like it will fetch only one record at a time, thats why its forward only like that.

My question here is if the DataReader is capable of fetching only one record at a time, why cant it be developed to fetch the previous row also and why its developed to fetch only the next row and not the previous row ?

Any appropriate reason why it is developed in a way that it cant fetch the previous row ?
Prabhu Raja15y ago
Hi mani,

For Example: In Array's, the Index Option Allows to get next and previous data. Like that why we Can't do the same by using DataReader?
Manikavelu Velayutham15y ago
Anyway its going to read only one row at a time, why cant it be a previous row ?
Prabhu Raja15y ago
Hi,

DataReaader is connected object and one can process the rows that are returned by query, one at a time. It discards every row after you have gone through it and so it is extremely fast.It contains only read-only data, so no updates are allowed using DataReaderobjects.

Thank You
Hemant Kumar15y ago
Hi Alok ,

A DataReader is a stream of data that is returned from a database query. When the query is executed, the first row is returned to the DataReader via the stream. The stream then remains connected to the database, poised to retrieve the next record. The DataReader reads one row at a time from the database and can only move forward, one record at a time. As the DataReader reads the rows from the database, the values of the columns in each row can be read and evaluated, but they cannot be edited.

Generally we use datareader ado.net control where we don't need go to previous row like binding a dropdown or data repeater control. To keep it light weighted microsoft support forward only functionality in datareader control.
Pravin More15y ago
Hi Alok,
because DataSet works as connected architecture . The DataReader reads one row at a time
from the database and can only move forward, one record at a time. when it reads next row it descards pervious row,thats the reason it cant go backward.In prohramming language it work as 1way linked list.

Thank You,
Pravin.