why MySql Enum mapping needs it's own table?

highjo · **Joined:** Mon Mar 30, 2009 2:47 pm **Posts:** 15

Hello guys!
i've been tried to map Java 5 enum type to mysql enum type and came accross this article http://weblog.dangertree.net/2007/09/23/mapping-java-5-enums-with-hibernate/ and couldn't understand why there should be a table to hold the enum details or elements.i was expecting it to be map to a field in the table.the other version i got is to map a string property to the enum like suggested here http://stackoverflow.com/questions/1076604/mysql-enum-with-hibernate but it doesn't seem to be what i want.is there any other way to achieve that?THanks for reading

Froestel · **Posted:** Mon Sep 28, 2009 2:52 pm

Hi highjo,

highjo wrote:

... and couldn't understand why there should be a table to hold the enum details or elements.i was expecting it to be map to a field in the table...

You should probably read this to understand why it is done this way: http://en.wikipedia.org/wiki/Database_normalization

CU
Froestel

rodrigo.ipince · **Joined:** Sun Nov 22, 2009 6:42 pm **Posts:** 7

Hi Froestel,

I see why someone would like to put the Enum details in another table. However, wouldn't that become expensive since it'll require you to perform a join? Sure, the Enum table is small, but still..

And even if it's wrong in principle, is there a way to achieve what the original poster asked? Since I'm sure my enum is never going to change and is only used in 1 class, I'd rather have it map to an enum column in the database.

If I don't specify the type of my Enum field in the xml mapping file, I see that Hibernate is adding a column in my db with type 'tinyblob' and a cryptic value. Yet it manages to correctly map the cryptic value back to the appropriate Enum in my POJO. It does what I want it to do, but doesn't seem ideal. I want the db column to be an enum and the values to be the possible enum values (strings). Can you help me achieve this? BTW, I'm using MySQL.

Thanks!

rodrigo.ipince · **Joined:** Sun Nov 22, 2009 6:42 pm **Posts:** 7

It seems the 'cryptic' value i was talking about is the serialized version of the Enum... It seems any Serializable class for which there's no explicit mapping defined will be pushed into the DB as a tinyblob...

Froestel · **Posted:** Mon Nov 23, 2009 6:17 am

Hi rodrigo.ipince,

have you tried to map the enum as a component? This could probably work.

Anyway, why care about the way the value is stored in the database? This should usually not matter.

CU
Froestel

P.S.: BTW, it is not necessarily a tinyblob that is used. You can determine the size by passing an appropriate long attribute value in the mapping.