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Topic: Explain what a diffgram is, and a good use for one?
Anamika singh
11 Oct 2010 at 03:37 AM
Explain what a diffgram is, and a good use for one?
Re: Explain what a diffgram is, and a good use for one?
12 Oct 2010 at 02:28 AM

The DiffGram is one of the two XML formats that you can use to render DataSet object contents to XML. A good use is reading database data to an XML file to be sent to a Web Service.
DiffGrams and DataSet
There are occasions when you want to compare the original data with the current data to get the changes made to the original data. One of the common example is saving data on Web Forms applications. When working with Web based data driven applications, you read data using a DataSet, make some changes to the data and sends data back to the database to save final data. Sending entire DataSet may be a costly affair specially when there are thousands of records in a DataSet. In this scenario, the best practice is to find out the updated rows of a DataSet and send only updated rows back to the database instead of the entire DataSet. This is where the DiffGrams are useful.
Note: Do you remember GetChanges method of DataSet? This method returns the rows that have been modified in the current version in a form of DataSet. This is how a DataSet knows the modified rows.
A DiffGram is an XML format that is used to identify current and original versions of data elements. Since the DataSet uses XML format to store and transfer data, it also use DiffGrams to keep track of the original data and the current data. When a DataSet is written as a DiffGram, not only a DiffGram stores original and current data, it also stores row versions, error information, and their orders.

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