{"id":83,"date":"2015-07-23T14:57:22","date_gmt":"2015-07-23T14:57:22","guid":{"rendered":"http:\/\/www.solewing.org\/blog\/?p=83"},"modified":"2015-07-23T16:27:38","modified_gmt":"2015-07-23T16:27:38","slug":"hibernate-envers-onetomany-list-and-ordercolumn","status":"publish","type":"post","link":"http:\/\/www.solewing.org\/blog\/2015\/07\/hibernate-envers-onetomany-list-and-ordercolumn\/","title":{"rendered":"Hibernate Envers, @OneToMany List, and @OrderColumn"},"content":{"rendered":"

Using Hibernate Envers<\/a> with a @OneToMany<\/code> association for a List<\/code> property that uses @OrderColumn<\/code> requires a little extra glue. Without this extra glue, Envers will throw a NullPointerException<\/code> in a lazy initializer when you try to load revisions.<\/p>\n

Suppose our domain model has a Sponsor entity. A Sponsor can have multiple business names, represented by a Sponsor Name entity. The names are ordered by preference, so we use a @OneToMany<\/code> with a List<\/code>. Here’s how we might map the Sponsor entity.<\/p>\n

[java]
\n@Entity
\n@Audited
\n@Access(AccessType.FIELD)
\npublic class SponsorEntity {<\/p>\n

@OneToMany(mappedBy = “sponsor”, fetch = FetchType.LAZY, orphanRemoval = true)
\n @OrderColumn(name = “name_index”)
\n private List names = new ArrayList<>();<\/p>\n

}
\n[\/java]<\/p>\n

And here’s the SponsorNameEntity.<\/p>\n

[java]
\n@Entity
\n@Audited
\n@Access(AccessType.FIELD)
\npublic class SponsorNameEntity {<\/p>\n

@Column(nullable = false)
\n private String name;<\/p>\n

@ManyToOne(optional = false, fetch = FetchType.LAZY)
\n private SponsorEntity sponsor;<\/p>\n

}
\n[\/java]<\/p>\n

If we use these entities with Hibernate Envers, we’ll get an NPE when we try to load revisions of the SponsorEntity<\/code>. It happens because the name_index<\/code> column specified by the @OrderColumn<\/code> annotation is not included in the audit table for SponsorNameEntity<\/code>.<\/p>\n

We can fix this easily, with an additional field on SponsorNameEntity<\/code> and an extra annotation on SponsorEntity<\/code>. The extra field on SponsorNameEntity<\/code> is used to expose the value of the order column as a field:<\/p>\n

[java]
\n@Entity
\n@Audited
\n@Access(AccessType.FIELD)
\npublic class SponsorNameEntity {<\/p>\n

\/\/ This field is used to capture the value of the column named
\n \/\/ in the @OrderColumn annotation on the referencing entity.
\n @Column(insertable = false, updatable = false)
\n private int name_index;<\/p>\n

@Column(nullable = false)
\n private String name;<\/p>\n

@ManyToOne(optional = false, fetch = FetchType.LAZY)
\n private SponsorEntity sponsor;<\/p>\n

}
\n[\/java]<\/p>\n

In SponsorEntity<\/code> we use an additional annotation to inform Envers about the field that contains the order column value:<\/p>\n

[java]
\n@Entity
\n@Audited
\n@Access(AccessType.FIELD)
\npublic class SponsorEntity {<\/p>\n

@OneToMany(mappedBy = “sponsor”, fetch = FetchType.LAZY, orphanRemoval = true)
\n @OrderColumn(name = “name_index”)
\n @AuditMappedBy(mappedBy = “sponsor”, positionMappedBy = “name_index”)
\n private List names = new ArrayList<>();<\/p>\n

}
\n[\/java]<\/p>\n

The positionMappedBy<\/code> attribute of the @AuditMappedBy<\/code> annotation informs Envers that the position of each entry in the list is given by the value of the name_index<\/code> field that we added to SponsorNameEntity<\/code>. It seems a little redundant, but we’re required to also specify the value of the mappedBy<\/code> attribute, which should be the same as the value given in the @OneToMany<\/code> annotation.<\/p>\n

If you discover that you need this fix after you’ve already got some revisions out there in your audit tables, don’t forget to<\/p>\n

    \n
  1. Add the column specified by @OrderColumn<\/code> to the appropriate audit table. In our example, this column goes into the audit table for SponsorNameEntity<\/code>.<\/li>\n
  2. Initialize the column value in each of the existing rows. You can usually query the table associated with the entity to get the appropriate index value — e.g. in our case we’d query the table for SponsorNameEntity<\/code> to get the name_index<\/code> column value and use it to update the corresponding rows in the audit table.<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"

    Using Hibernate Envers with a @OneToMany association for a List property that uses @OrderColumn requires a little extra glue. Without this extra glue, Envers will throw a NullPointerException in a lazy initializer when you try to load revisions. Suppose our domain model has a Sponsor entity. A Sponsor can have multiple business names, represented by […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[14],"tags":[28,27,16,29],"class_list":["post-83","post","type-post","status-publish","format-standard","hentry","category-javaee","tag-envers","tag-hibernate","tag-javaee-2","tag-jpa"],"_links":{"self":[{"href":"http:\/\/www.solewing.org\/blog\/wp-json\/wp\/v2\/posts\/83","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.solewing.org\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.solewing.org\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.solewing.org\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.solewing.org\/blog\/wp-json\/wp\/v2\/comments?post=83"}],"version-history":[{"count":7,"href":"http:\/\/www.solewing.org\/blog\/wp-json\/wp\/v2\/posts\/83\/revisions"}],"predecessor-version":[{"id":90,"href":"http:\/\/www.solewing.org\/blog\/wp-json\/wp\/v2\/posts\/83\/revisions\/90"}],"wp:attachment":[{"href":"http:\/\/www.solewing.org\/blog\/wp-json\/wp\/v2\/media?parent=83"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.solewing.org\/blog\/wp-json\/wp\/v2\/categories?post=83"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.solewing.org\/blog\/wp-json\/wp\/v2\/tags?post=83"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}