Store Map<Enum, Enum> as String

Question

I need help with storing a map in JPA2, where both keys and values are enums (Map<Enum, Enum>). With Hibernate as my JPA provider it stores the enums as a blob but I need the data stored as strings. I tried the following annotations to fix this problem:

@ElementCollection(fetch = FetchType.EAGER)
@MapKeyEnumerated(value = EnumType.STRING)
public Map<Enum, Enum> getElementsMap() {
 return elementsMap;
}

But the data is still being stored into the DB as blob. Has anyone solved this problem?

• Niklas B.: Saving a map as a string doesn't sound sensible at all. Have you heard of data normalization?
• user1289877: Sorry, I write this question in wrong manner, now it's fixed, I mean keys and it's values.
• Niklas B.: You can just use toString() on both the keys and values. What's the problem?
• user1289877: I don't thik so that this is the very basic stuff, look at this post: forum.hibernate.org/viewtopic.php?f=1&t=999270&start=0 Maybe you should consult a Java beginners book.
• user1289877: @Niklas B. Before you write something and someone recommended that he should read something, think twice! If you really don't understand a problem and don't know the specific solution, please don't spam questions with your irrelevant comments and try to study somethink before you post your answer.

Answer 1

@Enumerated is used to to define type for value. Following maps to table where column for both key and value are varchars and name of the enum will be saved:

@Enumerated(EnumType.STRING)
@ElementCollection(fetch = FetchType.EAGER)
@MapKeyEnumerated(value = EnumType.STRING)
public Map<MyEnum, MyOtherEnum> elementsMap = new HashMap<>();

It will produce roughly following table:

[NAME_OF_ENTITY]_ELEMENTSMAP (
 NAME_OF_ENTITY_ID INTEGER, 
 ELEMENTSMAP VARCHAR(255), 
 ELEMENTSMAP_KEY VARCHAR(255)
)

• user1289877: Thanks for your post, I tried it, but didn't help me. I use postgresql db and hibernate create int8, bytea, bytea data types in table.

Answer 2

Almost each and every Java Object has a toString() method If you want to represent your Map in the database, then I suggest this be your option.

However I have to ask are you sure it is the MAP you wish to store and not the elements of the keys or values?

• user1289877: Yes, it's the keys and it's values, Sorry I'm starting with JPA2 and hibernate, can you post the here the changes in code which must I do to store this keys and values as String?