Which .NET data type is best for mapping the NUMBER Oracle data type in NHibernate?

I've seen some examples in which decimal is used in NHibernate projects for mapping to whole number columns in Oracle. Right now I'm using int and long in my program.

What are the advantages of decimal over int/long? Does it perform better?

> I've seen decimal used instead of int/long in various examples. I'm just trying to understand why

That's probably because .NET decimal and Oracle NUMBER maps a bit better than long and NUMBER and it also gives you more flexibility. If you at a later stage add a scale in the Oracle column then you wouldn't have to change datatype if you already used decimal.

decimal is certainly slower than int and long since the later two are supported in hardware. That said, you have to crunch some serious amount of data for it to make any difference. I still think that you should use long if that that's what you're dealing with and then you should also let the table column definitions represent that. NUMBER(18,0) for long and so on.

The reason decimal maps a little better is that long is 64 bits and decimal is (kind of) 128 bits.

.NET

> > Type: decimal
> > Approximate Range: ±1.0 × 10^−28 to ±7.9 × 10^28
> > Precision: 28-29 significant digits

> > Type: long
> > Range: –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
> > Precision: 18 (19 for ulong) significant digits

Oracle

NUMBER defaults to 38 significant digits and scale 0 (integer).

> > Type: NUMBER
> > Range: +- 1 x 10^-130 to 9.99...9 x 10^125
> > Precision: 38 significant digits

Microsoft is aware of the problem and notes

> This data type is an alias for the > NUMBER(38) data type, and is designed > so that the OracleDataReader returns a > System.Decimal or OracleNumber instead > of an integer value. Using the .NET > Framework data type can cause an > overflow.

Come to think of it you actually need BigInteger to be able to represent the same number of significant digits as to what NUMBER defaults to. I've never seen anyone do that and I would suppose it's a very rare need. Also BigInteger still wouldn't cut it since NUMBER can be of positive and negative infinity.

[.NET: Int32] = [Oracle:NUMBER(2)..NUMBER(9)*] 
[.NET: Int64] = [Oracle:NUMBER(10)..NUMBER(18)*]
[.NET: Double] = [Oracle:NUMBER(x, 0)..NUMBER(x, 15)*]
[.NET: Double] = [Oracle: FLOAT]
[.NET: Decimal] = [Oracle:NUMBER]  

NUMBER(1,0) 	=> Boolean    		
NUMBER(5,0)	    => Int16/short.MaxValue == 32767    
NUMBER(10,0)	=> Int32/int.MaxValue == 2,147,483,647    
NUMBER(19,0)	=> Int64/long.MaxValue == 9,223,372,036,854,775,807