How to store an enumeration?

nbhatia · **Posted:** Wed Aug 31, 2005 12:49 am

I have an Order class that uses a simple enumeration:

Code:

    public enum OrderStatus
    {
        CREATED,
        MODIFIED,
        SUBMITTED,
        CLOSED
    }

    public class Order
    {
        private OrderStatus status;
        ...
    }

What is the recommended approach to save this enumeration using NHibernate?

- What does the mapping file look like?
- What is the column type in the database? Should the enumerations be stored as numbers of strings?

Thanks.

KPixel · **Posted:** Wed Aug 31, 2005 4:33 am

Read:
Char enumerations
Enumeration Bug?

nbhatia · **Joined:** Sun Sep 25, 2005 11:35 pm **Posts:** 57

Thanks. After reading these posts it appears that it is easier to store enums as numbers in the database, which is fine with me. Couple of questions:

1) I tried the following two mappings. They both seem to work fine and there is no change in behavior. Is this intentional? (perhaps because enums are the same as Int32 in .NET). Which one is the preferred way?

Code:

<property name="Status" column="Status" type="TimeTrackerDomain.TimecardStatus, TimeTrackerDomain" />

<property name="Status" column="Status" type="Int32" />

2) The "Hibernate in Action" book talks about storing enums as VARCHARs (page 209 - "Using enumerated types"). Is this approach supported in NHibernate?

KPixel · **Posted:** Fri Sep 02, 2005 5:40 am

1) IMO, you should use the first mapping (or you can omit it and NHibernate will use reflection to find it)

2) I don't know how Java/Hibernate handle enums, but I don't think that NHibernate support that.

BillHawes · **Posted:** Mon Sep 05, 2005 4:42 am

You can use the NHibernate.Type.EnumStringType class to store your enumerations as VARCHAR or CHAR. This is an abstract class which you can easily subclass.

From the SDK docs, if you have the following enum

Code:

public enum MyEnum 
{
    On,
    Off,
    Dimmed
}

then you subclass EnumStringType as follows

Code:

public class MyEnumStringType : NHibernate.Type.EnumStringType
{
    public MyEnumStringType()
        : base( typeof( MyEnum ) )
    {
    }
}

And use a mapping like

Code:

...
    <property name="Status" type="MyEnumStringType, AssemblyContaining" />
...

This will map to a VARCHAR column in the database, and use the enum member names ("On", "Off", "Dimmed" in the example) instead of the numeric values.