Working on a bug today, there was a list of items with a set of sub items coming back from the database via Hibernate. Something like this in pseudocode:<\/p>\n
\r\n@Entity\r\n@Table(name = "PARENT", schema = "USER")\r\npublic class Parent implements Serializable {\r\n\r\nprivate Long id;\r\nprivate String name;\r\nprivate List<Child> childList = new ArrayList<Child>();\r\n\r\n@Id\r\n@SequenceGenerator\r\n@Column(name="PARENT_ID")\r\npublic Long getId() {\r\nreturn id;\r\n}\r\n\r\npublic void setId(Long id) {\r\nthis.id = id;\r\n}\r\n\r\n@Id\r\n@Column\r\npublic String getName() {\r\nreturn name;\r\n}\r\n\r\npublic void setName(String name) {\r\nthis.name = name;\r\n}\r\n\r\n@OneToMany(mappedBy = "parent",fetch = FetchType.EAGER)\r\n@Cascade(CascadeType.ALL)\r\npublic List<Child> getChildList() {\r\nreturn childList;\r\n}\r\n\r\npublic void setChildList(List<Child> childList) {\r\nthis.childList = childList;\r\n}\r\n}\r\n\r\n@Entity\r\n@Table(name = "CHILD", schema = "USER")\r\npublic class Child implements Serializable {\r\n\r\nprivate Long id;\r\nprivate String name;\r\nprivate Parent parent;\r\n\r\n@Id\r\n@SequenceGenerator\r\n@Column(name="CHILD_ID")\r\npublic Long getId() {\r\nreturn id;\r\n}\r\n\r\npublic void setId(Long id) {\r\nthis.id = id;\r\n}\r\n\r\n@Id\r\n@Column\r\npublic String getName() {\r\nreturn name;\r\n}\r\n\r\npublic void setName(String name) {\r\nthis.name = name;\r\n}\r\n\r\n@ManyToOne\r\n@JoinColumn(name = "PARENT_ID")\r\npublic Parent getParent() {\r\nreturn parent;\r\n}\r\n\r\npublic void setParent(Parent parent) {\r\nthis.parent = parent;\r\n}\r\n}\r\n\r\n@Repository\r\npublic class ParentDao implements SomeGenericDao {\r\n\r\npublic List<JasperReportTemplate> getAllActiveTemplates(Long firmId) {\r\nfinal Criteria criteria = getCurrentSession()\r\n .createCriteria(getModelClass())\r\n .(DO SOME CRITERIA ETC>);\r\nreturn criteria.list();\r\n}\r\n}\r\n<\/pre>\nHere are your data sets for PARENT(parent_id, name):<\/p>\n
And your data sets for CHILD(child_id,parent_id(foreign key),name)<\/p>\n
When you try to make a list of *just* PARENT with this configuration you end up getting:<\/p>\n
But what you want is this:<\/p>\n
It’s because of that EAGER fetch — it forces everything to be in ONE BIG QUERY with all the tables so you get a Cartesian result. What you really want is just unique PARENT values.<\/p>\n
Solutions<\/strong><\/p>\n Removing “EAGER”<\/strong><\/p>\n First, if you remove the EAGER, you won’t be loading any CHILD data. This could be problematic because the CHILD data won’t be available without making another data call to hydrate those objects. Depends on what you want.<\/p>\n Returning a Set instead of a List from the DAO<\/strong><\/p>\n Another solution is something like this in the DAO in your java, that will return a set object that automatically filters the unique objects:<\/p>\n Supposably this is a workaround. it does work though.<\/p>\n Setting @Fetch<\/strong><\/p>\n yet another solution, and one that I use, is to just set @Fetch on the child property:<\/p>\n I’ve also had success with using FetchMode.SELECT. This forces Hibernate to do a subquery on the child instead of one massive query — and you get all the data back.<\/p>\n","protected":false},"excerpt":{"rendered":" Working on a bug today, there was a list of items with a set of sub items coming back from the database via Hibernate. Something like this in pseudocode: Here are your data sets for PARENT(parent_id, name): (1,”parent1″) (2,”parent2″) And your data sets for CHILD(child_id,parent_id(foreign key),name) (1,1,”child1″) (2,1,”child2″) (3,2,”child3″) (4,2,”child4″) When you try to make […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"http:\/\/10kdev.net\/index.php?rest_route=\/wp\/v2\/posts\/620"}],"collection":[{"href":"http:\/\/10kdev.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/10kdev.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/10kdev.net\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/10kdev.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=620"}],"version-history":[{"count":15,"href":"http:\/\/10kdev.net\/index.php?rest_route=\/wp\/v2\/posts\/620\/revisions"}],"predecessor-version":[{"id":634,"href":"http:\/\/10kdev.net\/index.php?rest_route=\/wp\/v2\/posts\/620\/revisions\/634"}],"wp:attachment":[{"href":"http:\/\/10kdev.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=620"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/10kdev.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=620"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/10kdev.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=620"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}\r\n Set = new LinkedHashSet();\r\n set.addAll(criteria.list());\r\n return set;\r\n<\/pre>\n
\r\n @OneToMany(mappedBy = "parent",fetch = FetchType.EAGER)\r\n @Cascade(CascadeType.ALL)\r\n @Fetch(FetchMode.SUBSELECT)\r\n public List<Child> getChildList() {\r\n return childList;\r\n }\r\n<\/pre>\n