@OneToMany Column Returns LazyInitializationException - Spring

Question

I have the following mapping in my User DTO to store a Map of user properties:

@Entity(name = "User")
public class User{

    @Id
    @Column(name = "Id")
    private long userId;

    @OneToMany
    @JoinColumn(name = "properties")
    private Map<Long, Property> properties= new LinkedHashMap<Long, LkpAIT>();

}

@Entity(name = "Property")
public class Property{

    @Id
    @Column(name = "Id")
    private long propertyId;

    @Column(name = "Name")
    private String propertyName;

} 

And the following @Controller method

@RequestMapping(value = "/getUser", produces = "application/json", method = RequestMethod.GET)
public @ResponseBody Page<LkpFeed> getLookupFeeds(Model model) {
    page = 1;
    Page<User> users = userRepo.getUsers(new PageRequest(page, 100)); //returns 100 users
    return feeds;
}

The @Controller method executes fine (all users are found) however when the return statement executes, I get the following error:

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.myapp.dto.Properties.properties, could not initialize proxy - no Session
    org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:575)
    org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:214)
    org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:155)
    org.hibernate.collection.internal.PersistentMap.isEmpty(PersistentMap.java:145)
    com.fasterxml.jackson.databind.ser.std.MapSerializer.serialize(MapSerializer.java:399)
    com.fasterxml.jackson.databind.ser.std.MapSerializer.serialize(MapSerializer.java:27)
    com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:505)
    com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:639)
    com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152)
    com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:100)

Based on the exception my properties field is what's causing the error. I've experimented with fetchTypes and PersistenceContexts but am currently at a loss. Any ideas?

Answer 1

You can do several things

1. add fetch Eager in @OneToMany

    @Entity(name = "User") public class User{ @Id @Column(name = "Id") private long userId; @OneToMany(fetch=FetchType.EAGER) @JoinColumn(name = "properties") private Map<Long, Property> properties= new LinkedHashMap<Long, LkpAIT>(); } 

2. Or if you don't want the Properties in your returned JSON when you want to list only the users. You can add a @JsonIgnore for properties

    @Entity(name = "User") public class User{ @Id @Column(name = "Id") private long userId; @JsonIgnore @OneToMany @JoinColumn(name = "properties") private Map<Long, Property> properties= new LinkedHashMap<Long, LkpAIT>(); }