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Ways to save enums in database

Asked 2008-10-23T14:11:15.093
149

What is the best way to save enums into a database?

I know Java provides name() and valueOf() methods to convert enum values into a String and back. But are there any other (flexible) options to store these values?

Is there a smart way to make enums into unique numbers (ordinal() is not safe to use)?

Update

Thanks for all awesome and fast answers! It was as I suspected.

However, a note to toolkit: That is one way. The problem is that I would have to add the same methods to each enum type that I create. That's a lot of duplicated code and, at the moment, Java does not support any solutions for this (a Java enum cannot extend other classes).

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We never store enumerations as numerical ordinal values anymore; it makes debugging and support way too difficult. We store the actual enumeration value converted to string:

public enum Suit { Spade, Heart, Diamond, Club }

Suit theSuit = Suit.Heart;

szQuery = "INSERT INTO Customers (Name, Suit) " +
          "VALUES ('Ian Boyd', %s)".format(theSuit.name());

and then read back with:

Suit theSuit = Suit.valueOf(reader["Suit"]);

The problem was in the past staring at Enterprise Manager and trying to decipher:

Name          Suit
------------  ----
Kylie Guénin  2
Ian Boyd      1

verses

Name          Suit
------------  -------
Kylie Guénin  Diamond
Ian Boyd      Heart

the latter is much easier. The former required getting at the source code and finding the numerical values that were assigned to the enumeration members.

Yes it takes more space, but the enumeration member names are short, and hard drives are cheap, and it is much more worth it to help when you're having a problem.

Additionally, if you use numerical values, you are tied to them. You cannot nicely insert or rearrange the members without having to force the old numerical values. For example, changing the Suit enumeration to:

public enum Suit { Unknown, Heart, Club, Diamond, Spade }

would have to become :

public enum Suit { 
      Unknown = 4,
      Heart = 1,
      Club = 3,
      Diamond = 2,
      Spade = 0 }

in order to maintain the legacy numerical values stored in the database.

How to sort them in the database

The question comes up: lets say i wanted to order the values. Some people may want to sort them by the enum's ordinal value. Of course, ordering the cards by the numerical value of the enumeration is meaningless:


                        
                        

                            answered 2008-10-23T14:21:58.300

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