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You should set ParentTableRelation for the DetailTables, which define the relation between the data in the master and detail view. Also make sure to set SelectParameters in the object data source for the detail table. For additional help read this help topic.
The GridView will automatically load needed data when expanded, and you do not need care about ItemCommand and Selecting events. Check the following attached demo. And if you are unable to resolve the issue, open a formal support ticket, and send us your code with the declaration of the grid and datasources.
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