Hibernate map an association as a map

Question

I have a MessengerData class which contains a list of resources. This my object MessengerData:

"messengerData":{  
   "fr":[  
    { 
      "messengerType":"ImageCategoryTitle",
      "imageURL":"https://assets.pernod-ricard.com/uk/media_images/test.jpg"
    }
    "EN":[
    {
      "messengerType":"ImageCategoryTitle",
      "imageURL":"https://assets.pernod-ricard.com/uk/media_images/test.jpg",
    }
]

This is how I define my object MessengerData:

@Entity
public class MessengerData
{

@Basic
@Id
@GeneratedValue(generator = "notification-system-uuid")
@GenericGenerator(name = "notification-system-uuid", strategy = "uuid")
private String messengerDataId;


@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER) /* , mappedBy = "idResource" */
@JoinTable(name = HemisTablesNames.MESSENGER_RESOURCES, joinColumns = @JoinColumn(name = "idResource"),
        inverseJoinColumns = @JoinColumn(name = "messengerDataId"))
private Map<String, Set<Resource>> resources;
}

But I am getting this exception: Use of @OneToMany or @ManyToMany targeting an unmapped class: com.ubiant.hemis.type.MessengerData.resources[java.util.Set]

Could someone help me with this ?

One of [these problems](https://stackoverflow.com/a/4956930/3959856) maybe? Resouce is not mapped with Hiberate — Jack Flamp, Sep 20 '18 at 13:22

Thomas · Accepted Answer · 2018-09-20T13:36:33.093

Hibernate doesn't seem to support multimaps (that's what resources is) directly but you could provide your own custom type like described here: https://xebia.com/blog/mapping-multimaps-with-hibernate/ .

However, since your data seems to be Json anyway you could go one more step and directly map the resources as json, i.e. into a text column (or a json column if the db supports it): http://fabriziofortino.github.io/articles/hibernate-json-usertype/

We're doing something similar, which on an outline looks like this (this is a generic type, in most cases a more specific POJO will be better):

 class JsonData extends HashMap<String, Object> { ... }

 //JsonbUserType is a custom implementation based on code like the one linked above
 class JsonDataUT extends JsonbUserType<JsonData > { ... }

Then in package-info.java of the package the user type is in we have this:

@TypeDefs ( {    
  @TypeDef ( name = "JsonDataUT ", typeClass = JsonDataUT.class, defaultForType = JsonData.class ),
  ... 
})
package our.package;

And our entities then just contain this:

@Column( name = "data_column")
private JsonData data;

One advantage of this is that we don't have to bother with more complex mappings, especially if types are dynamic.

One (major) disadvantage, however, is that you can't use that property in query conditions since Hibernate wouldn't know how to filter in a json column (we're using Postgres so it would really be a jsonb typed column, hence the usertype name) and afaik there's not reasonable way to provide custom functions etc. to enable things like where data.someFlag is true in HQL.

Hibernate map an association as a map

1 Answers1