“Specified cast is not valid” when populating DataTable from OracleDataAdapter.Fill()

Question

I can\'t seem to find this question anywhere on Google (or StackOverflow), which really surprised me, so I\'m putting it on here to help others in the same situation.

I

Answer 1

Answering my own question:

So it seems that the Oracle number type can hold many more decimal places than the C# decimal type and if Oracle is trying to return more than C# can hold, it throws the InvalidCastException.

Solution?

In your sql, round any results that might have too many decimal places to something sensible. So I did this:

SELECT acct_no, ROUND(market_value/mv_total, 8)  -- rounding this division solves the problem
FROM myTable
WHERE NVL(market_value, 0) != 0
AND NVL(mv_total, 0) != 0

And it worked.

The take away is: Incompatibility between Oracle number type and C# decimal. Restrict your Oracle decimal places to avoid the invalid cast exceptions.

Hope this helps someone else!