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How to map a Map<String,String> using annotations?

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borkert

Post subject: How to map a Map<String,String> using annotations?

Posted: Tue Mar 27, 2012 9:50 am

Newbie

Joined: Tue Nov 01, 2005 12:38 pm
Posts: 12

Hello,

I'm trying to switch from XML configuration to annotation based configuration, but I'm stuck with a problem that I thought should not be that hard to solve, sadly I could not find anything about it that works.

I got a class named Event, the Event contains a Map<String,String> of the Events attributes. With the XML configuration this can be mapped easily:

Code:

        <map access="field" name="attributes" table="eventattributes" lazy="false">
            <key column="id"/>
            <index column="key" length="1024" type="string"/>
            <element column="value" length="4096" type="string"/>
        </map>

My current approach with annotations is the following:

Code:

    @ElementCollection(targetClass = String.class, fetch = FetchType.EAGER)
    @MapKeyClass(String.class)
    @AttributeOverrides({
            @AttributeOverride(name="key", column=@Column(name = "key", length = 1024)),
            @AttributeOverride(name="value", column=@Column(name = "value", length = 4096))
    })
    private Map<String,String> attributes = new TreeMap<String,String>();

Using this causes a exception I do not understand:

Code:

Caused by: org.hibernate.MappingException: Repeated column in mapping for collection: xxx.domain.EventDO.attributes column: count
   at org.hibernate.mapping.Collection.checkColumnDuplication(Collection.java:341)

@CollectionOfElements worked, but it is deprecated, and I don't know how to adjust the column sizes.

Regards,

Sven

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borkert

Post subject: Re: How to map a Map<String,String> using annotations?

Posted: Wed Mar 28, 2012 10:39 am

Newbie

Joined: Tue Nov 01, 2005 12:38 pm
Posts: 12

No idea anyone? ö.ö

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borkert

Post subject: Re: How to map a Map<String,String> using annotations?

Posted: Thu Mar 29, 2012 8:05 am

Newbie

Joined: Tue Nov 01, 2005 12:38 pm
Posts: 12

Now I found out that the following nearly works:

Code:

    @ElementCollection(fetch = FetchType.EAGER)
    @MapKeyColumn(name = "key", length = 1024)
    @Column(name = "value", length = 4069)
    private Map<String,String> attributes = new TreeMap<String,String>();

Sadly this causes a join over the attribues table, so I get duplicate results. I understand why I join causes duplicate results, this is described in the FAQ, but I do not understand why Hibernate tries to fill this Map with a join at all. The XML based configuration I used first causes a query to the attributes table for each row returned, so there is no join and there are no duplicate results.

Regards,

Sven

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borkert

Post subject: Re: How to map a Map<String,String> using annotations?

Posted: Thu Mar 29, 2012 9:44 am

Newbie

Joined: Tue Nov 01, 2005 12:38 pm
Posts: 12

I found the solution:

Code:

    @ElementCollection(fetch = FetchType.EAGER)
    @Fetch(value = FetchMode.SELECT)
    @MapKeyColumn(name = "key", length = 1024)
    @Column(name = "value", length = 4069)
    private Map<String,String> attributes = new TreeMap<String,String>();

Setting the FetchMode to SELECT causes Hibernate to do a select to the attributes table for every result object it returns. So there is no join and no duplicate results.

Still wondering why the default mode is to use a join, I can't imagine any use for that.

Regards,

Sven

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