Enum in Hibernate, persisting as an enum

问题:

In my MySQL database, there's the column "gender enum('male','female')"

I've created my enum "com.mydomain.myapp.enums.Gender", and in my Person entity I'm defined "Gender gender".

Now I'd want to keep the enum type in my MySQL database, but when I launch my application I get:

Wrong column type in MyApp.Person for column Gender. Found: enum, expected: integer

Why is this? This would be the equivalent as if I'd annotated my "Gender gender" with "@Enumerated(EnumType.ORDINAL)", which I haven't. EnumType seems only to be able to be either ORDINAL or STRING, so how do I specify that it should treat the field as an enum, not as an int? (not that there's much difference, but enough for it to get upset about it.)

回答1:

My understanding is that MySQL enum type is very proprietary and not well supported by Hibernate, see this comment from Gavin King (this related issue is a bit different but that's not the important part).

So, I actually think that you'll have to use your own UsereType and I'd recommend to use the Flexible solution - working version from the Java 5 EnumUserType (see Appfuse's Java 5 Enums Persistence with Hibernate for an example).

Personally, I'd just forget the idea to use MySQL enum, I'm not convinced that the "benefits" are worth it (see this answer for more details).

回答2:

If you give Hibernate a column definition, it won't try to guess one:

@Column(columnDefinition = "enum('MALE','FEMALE')") @Enumerated(EnumType.STRING) private Gender gender; 

If you aren't relying on Hibernate to generate your schema for any reason, you don't even have to provide real values for the columnDefinition. This way, you remove an instance where you need to keep the values in sync. Just keep your Java enum and your Liquibase or SQL script in sync:

@Column(columnDefinition = "enum('DUMMY')") @Enumerated(EnumType.STRING) private ManyValuedEnum manyValuedEnum; 

回答3:

Try to use @Enumerated(EnumType.STRING) and define your enum like this

enum Gender {   male,   female } 

Note lower case values.

This will work at least with VARCHAR columns. It will store enum as string 'male' or 'female'.

回答4:

not sure why it is not in Hibernate documentation but you can do this

com.a.b.MyEnum         12              

回答5:

Not for this case but if someone is using XML mapping:

com.myorg.persistence.data.State   

The database column type must be numeric e.g. tinyint on a mysql to make reading ordinal values possible.

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