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If you would like to set how many rows can be selected in a `CGridView you would have to set selectableRows by giving it a value to the column that puts a checkbox CCheckBoxColumn to the grid.
Example:
[ 'id' => 'checkitems', 'class' => 'CCheckBoxColumn', 'selectableRows' => 100]
Setting it like below it would allow selecting only one row at a time:
[ 'id' => 'checkitems', 'class' => 'CCheckBoxColumn']