check empty datagridview columns

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C#

i have one datagridview control and one submit button in my form. i have taken four columns in datagridview. what i want is, on click of the submit button first it will check, is there any null or empty column in grid view. if so, then it will show message box "Enter the value" otherwise all the records should be saved in database.
And one more thing records should be saved only a single time if the code is running in the loop.. i will be very thankful of yours if you give me solution....