Specified cast not valid.

Casts and the Convert methods work in slightly different ways.

As you know, row["ID"] returns an object reference. In this particular example, the object is actually a boxed Int64 (i.e. long in C#) with a value of 38990.

In order to unbox this object, you need to cast it to its exact type i.e. long, though there's nothing to stop you then casting that to another compatible type such as decimal.

So, I'd expect this line to work:

decimal d = (decimal)(long)row["ID"];

In the case of Convert.ToDecimal(object), all that's necessary is that whatever the object actually is can be represented as a decimal. The underlying code actually calls Int64's IConvertible.ToDecimal() method and in this case there's no problem in converting the long value directly to a decimal.

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Vulpes13y ago
Accepted answer
Casts and the Convert methods work in slightly different ways.

As you know, row["ID"] returns an object reference. In this particular example, the object is actually a boxed Int64 (i.e. long in C#) with a value of 38990.

In order to unbox this object, you need to cast it to its exact type i.e. long, though there's nothing to stop you then casting that to another compatible type such as decimal.

So, I'd expect this line to work:

decimal d = (decimal)(long)row["ID"];

In the case of Convert.ToDecimal(object), all that's necessary is that whatever the object actually is can be represented as a decimal. The underlying code actually calls Int64's IConvertible.ToDecimal() method and in this case there's no problem in converting the long value directly to a decimal.
Premkumar Ekkaladevi13y ago
Thanks - that was a good explanation.