Hi I have a two tables like below .
1) Task - id,name
2) Resource - id,name,defaultTask(foreign key to Task.id)
The mapping is one to Many - one task can have many resource.
The code for Task is like below.
#Entity
public class Task implements Serializable {
private long m_id;
private String m_name;
#Id
#GeneratedValue(
strategy = GenerationType.AUTO
)
public long getId() {
return this.m_id;
}
public void setId(long id) {
this.m_id = id;
}
public String getName() {
return this.m_name;
}
public void setName(String name) {
this.m_name = name;
}
#OneToMany
#JoinColumn(
name = "defaultTask"
)
private List<Resource> m_relatedResources;
public List<Resource> getrelatedResources() {
return m_relatedResources;
}
public void setrelatedResources(List<Resource> relatedResources) {
m_relatedResources = relatedResources;
}
And the code for Resource class is like below.
#Entity
public class Resource implements Serializable {
private Long m_id;
private String m_name;
#Id
#GeneratedValue(
strategy = GenerationType.AUTO
)
public Long getId() {
return this.m_id;
}
public void setId(Long id) {
this.m_id = id;
}
public String getName() {
return this.m_name;
}
public void setName(String name) {
this.m_name = name;
}
Task m_task;
#ManyToOne
#JoinColumn(
name = "defaultTask"
)
public Task getTask() {
return this.m_task;
}
public void setTask(Task task) {
this.m_task = task;
}
}
When i execute it I am getting an error like
Initial SessionFactory creation failed.org.hibernate.MappingException: Could not determine type for: java.util.List, for columns: [org.hibernate.mapping.Column(relatedResources)]
What have i done wrong ?How can i fix the problem ?
You can't apply annotations to methods or fields randomly. Normally, you should apply your annotations the same way as #Id..
In Task class OneToMany should be like
#OneToMany
#JoinColumn(
name = "defaultTask"
)
public List<Resource> getrelatedResources() {
return m_relatedResources;
}
Field access strategy (determined by #Id annotation). Put any JPA related annotation right above each method instead of field / property as for your id it is above method and it will get you away form exception.
Also there appears to be an issue with your bidrectional mapping metntioned by #PredragMaric so you need to use MappedBy which signals hibernate that the key for the relationship is on the other side. Click for a really good question on Mapped by.
Many mistakes here:
you're annotating fields sometimes, and getters sometimes. Half of the annotation will be ignored: you must be consistent. It's one or the other.
You're not respecting the Java Bean naming conventions. The getter must be getRelatedResources(), not getrelatedResources().
A bidirectional association must have an owner side and an inverse side. In a OneToMany, the One is always the inverse side. The mapping should thus be:
.
#ManyToOne
#JoinColumn(name = "defaultTask")
public Task getTask() {
return this.m_task;
}
and
#OneToMany(mappedBy = "task")
public List<Resource> getRelatedResources() {
return m_relatedResources;
}
I also strongly advise you to respect the Java naming conventions. Variables should be named id and name, not m_id and m_name. This is especially important if you choose to annotate fields.
You're mixing annotating fields and getters in the same entity, you should move your #OneToMany to a getter
#OneToMany
#JoinColumn(mappedBy = "task")
public List<Resource> getrelatedResources() {
return m_relatedResources;
}
and yes, as the others mentioned, it should be mappedBy = "task". I'll upvote this teamwork :)
#JoinColumn is only used on owner's side of the relation, ToOne side, which is Resource#task in your case. On the other side you should use mappedBy attribute to specify bidirectional relation. Change your Task#relatedResources mapping to this
#OneToMany(mappedBy = "task")
private List<Resource> m_relatedResources;
Also, as #Viraj Nalawade noticed (and others, obviously), mapping annotations should be on fields or properties, whatever is used for #Id takes precedence. Either move #Id to field, or move #OneToMany to getter.
Related
I have a enum of few status value
NEW, REVIEWD, PUBLISHED, PENDING, UPDATED, SPAM, DUPLICATE, IRRELEVANT, UNPUBLISHED
I don't want to use them as enumerated so created one entity for that. For convenient I want to keep a column in entity to initialize status from enum and convert that enumerated value to a Object of status entity. for this..
I have two entity. I want to refer a column with value from another entity.
Basically I want to initialize a object with formula.
Entities are
#Entity
#Table(name = "event_status")
public class EventStatus {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name="eventStatusId")
private Integer eventStatusId;
#Enumerated(EnumType.STRING)
#Column(unique = true,name="eventStatusType")
private EventStatusType eventStatusType;
public EventStatus() {
this(EventStatusType.NEW);
}
public EventStatus(EventStatusType eventStatusType) {
super();
this.eventStatusType = eventStatusType;
}
public Integer getEventStatusId() {
return eventStatusId;
}
public EventStatusType getEventStatusType() {
return eventStatusType;
}
public void setEventStatusId(Integer eventStatusId) {
this.eventStatusId = eventStatusId;
}
public void setEventStatusType(EventStatusType eventStatusType) {
this.eventStatusType = eventStatusType;
}
}
I have another entity in which I am referring object of this entity
#Entity
#Table(name = "event_")
#Inheritance(strategy = InheritanceType.JOINED)
public abstract class Event implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#Column(name = "id_")
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
#Transient
public EventStatusType eventStatusType = EventStatusType.NEW;
#ManyToOne(fetch = FetchType.EAGER, targetEntity = EventStatus.class)
#Formula("select * from event_status where eventStatusId= 1")
private EventStatus status;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public EventStatus getStatus() {
System.out.println("Event.getStatus() " + status);
return status;
}
public void setStatus(EventStatus status) {
System.out.println("Event.setStatus()");
this.status = status;
}
}
This is not giving any exception but not initializing this value.
Is it possible to initialize this EntityStatus with value of eventStatusType in Event entity
I would like to explain that based on the documentation:
5.1.4.1.5. Formula
Sometimes, you want the Database to do some computation for you rather than in the JVM, you might also create some kind of virtual column. You can use a SQL fragment (aka formula) instead of mapping a property into a column. This kind of property is read only (its value is calculated by your formula fragment).
#Formula("obj_length * obj_height * obj_width")
public long getObjectVolume()
The SQL fragment can be as complex as you want and even include subselects.
...
5.1.7.1. Using a foreign key or an association table
...
Note
You can use a SQL fragment to simulate a physical join column using the #JoinColumnOrFormula / #JoinColumnOrformulas annotations (just like you can use a SQL fragment to simulate a property column via the #Formula annotation).
#Entity
public class Ticket implements Serializable {
#ManyToOne
#JoinColumnOrFormula(formula="(firstname + ' ' + lastname)")
public Person getOwner() {
return person;
}
...
}
Also, we should use insertable = false, updatable = false, because such mapping is not editable
I have some trouble with Hibernate 4 and inheritance:
I use a ChildData class which inherit from BaseData by a JOIN inheritance strategy. My mapping is done by annotation in classes.
Everything is working fine except that when I delete a ChildData instance (with session.delete() or with a Hql query) the BaseData entry is also deleted.
I understand that in most case this is the awaited behavior, but for my particular case, I would like to preserve the BaseData entry no matter what for history purpose.
In other words I want all actions on the child class to be cascaded to base class except deletion.
I have already tried #OnCascade on the child class, with no success.
Is it a way to achieve this by code or do I have to use a SQL Trigger ON DELETE ?
EDIT :
Base Class
#Entity
#Table(name = "dbBenchHistory", uniqueConstraints = #UniqueConstraint(columnNames = "Name"))
#Inheritance(strategy = InheritanceType.JOINED )
public class DbBenchHistory implements java.io.Serializable {
private int id;
private String name;
private String computer;
private String eap;
private Date lastConnexion;
private Set<DbPlugin> dbPlugins = new HashSet<DbPlugin>(0);
private Set<DbSequenceResult> dbSequenceResults = new HashSet<DbSequenceResult>(
0);
public DbBenchHistory() {
}
public DbBenchHistory(int id, String name) {
this.id = id;
this.name = name;
}
public DbBenchHistory(int id, String name, String computer, String eap,
Date lastConnexion, Set<DbPlugin> dbPlugins,
Set<DbSequenceResult> dbSequenceResults) {
this.id = id;
this.name = name;
this.computer = computer;
this.eap = eap;
this.lastConnexion = lastConnexion;
this.dbPlugins = dbPlugins;
this.dbSequenceResults = dbSequenceResults;
}
#Id
#Column(name = "Id", unique = true, nullable = false)
#GeneratedValue(strategy=GenerationType.IDENTITY)
public int getId() {
return this.id;
}
public void setId(int id) {
this.id = id;
}
//Getters/Setters
Child Class :
#Entity
#Table(name = "dbBench")
#OnDelete(action=OnDeleteAction.NO_ACTION)
public class DbBench extends DbBenchHistory {
private Set<DbProgram> dbPrograms = new HashSet<DbProgram>(0);
private Set<DbUser> dbUsers = new HashSet<DbUser>(0);
public DbBench() {
}
public DbBench(Set<DbProgram> dbPrograms,
Set<DbUser> dbUsers) {
this.dbPrograms = dbPrograms;
this.dbUsers = dbUsers;
}
//Getters/Setters
But I'm starting to think that I was wrong from the beginning and that inheritance was not the good way to handle this. If nothing shows up I will just go for BenchHistory - Bench being a simple one-to-one relationship
EDIT2 :
I edit while I can't answer my own question for insuficient reputation
I feel completly stupid now that I found the solution, that was so simple :
As I said, I was using hibernate managed methods : session.delete() or hql query. Hibernate was doing what he was supposed to do by deletintg the parent class, like it would have been in object inheritance.
So I just bypass hibernate by doing the deletion of the child class with one of the simplest SqlQuery on earth. And the base class entry remain untouched.
I understand that I somehow violate the object inheritance laws, but in my case it is really handy.
Thanks to everyone for your time, and believ me when I say I'm sorry.
I don't think Hibernate/JPA supports this. What you basically want is conversion from a subclass to a superclass, and not a cascading delete. When you have an object of the subclass, the members from the superclass are treated no different than the members of the subclass.
This can be solved through writing some logic for it though:
public void deleteKeepSuperclassObject(final ChildData childData) {
final BaseData baseDataToKeep = new BaseData();
//populate baseDataToKeep with data from the childData to remove
em.persist(baseDataToKeep);
em.remove(childData);
}
I'm annotating my domain model for a shop (with JPA 2, using a Hibernate Provider).
In the shop every product can have a Category. Each category can be assigned to several super- and subcategories, meaning a category "candles" can have "restaurant" and "decoration" as parents and "plain candles" and "multi-wick candles" as children, etc.
Now I want to avoid cyclic references, i. e. a category "a" that has "b" as its parent which in turn has "a" as its parent.
Is there a way to check for cyclic references with a constraint in JPA? Or do I have to write some checks myself, maybe in a #PostPersist-annotated method?
Here's my Category class:
#Entity
public class Category {
#Id
#GeneratedValue
private Long id;
private String name;
#ManyToMany
private Set<Category> superCategories;
#ManyToMany(mappedBy="superCategories")
private Set<Category> subCategories;
public Category() {
}
// And so on ..
}
I believe you would have to check this through a business rule in your code. Why don't you separate these ManyToMany mappings in a separate Entity ? Like for example:
#Entity
#Table(name = "TB_PRODUCT_CATEGORY_ROLLUP")
public class ProductCategoryRollup {
private ProductCategory parent;
private ProductCategory child;
#Id
#GeneratedValue
public Integer getId() {
return super.getId();
}
#Override
public void setId(Integer id) {
super.setId(id);
}
#ManyToOne(fetch=FetchType.LAZY)
#JoinColumn(name="ID_PRODUCT_CATEGORY_PARENT", nullable=false)
public ProductCategory getParent() {
return parent;
}
public void setParent(ProductCategory parent) {
this.parent = parent;
}
#ManyToOne(fetch=FetchType.LAZY)
#JoinColumn(name="ID_PRODUCT_CATEGORY_CHILD", nullable=false)
public ProductCategory getChild() {
return child;
}
public void setChild(ProductCategory child) {
this.child = child;
}
}
In this way, you could before Saving a new entity, query for any existing Parent-Child combination.
I know I come back to the problem after several years but, I faced this problem, followed all of your resolutions and it didn't work for me. But I found the best solution using #JsonIgnoreProperties which solved the problem perfectly. In fact, I injected #JsonIgnoreProperties into the entity classes linked by a mapping like here:https://hellokoding.com/handling-circular-reference-of-jpa-hibernate-bidirectional-entity-relationships-with-jackson-jsonignoreproperties/
I'm coming from a C# entity framework background and looking at JPA in a Java project so I'm hoping that what I'm facing is just a conceptual problem.
I've got a legacy database that I can't alter the schema of and I need to write a DAL.
I've generated (simplified for the example) the following entities...
#Entity
#Table(name = "crag", catalog = "rad_dbo")
public class CragEntity {
private int id;
#Column(name = "id")
#Id
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
private int fkSubRegionId;
#Column(name = "fk_subRegionId")
#Basic
public int getFkSubRegionId() {
return fkSubRegionId;
}
public void setFkSubRegionId(int fkSubRegionId) {
this.fkSubRegionId = fkSubRegionId;
}
}
and
#Table(name = "subRegion", catalog = "rad_dbo")
#Entity
public class SubRegionEntity {
private int id;
#Column(name = "id")
#Id
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
}
I've tried adding a relationship to CragEntity so that I can access its subRegion
#ManyToOne
#JoinColumn(name="fk_SubRegionId",nullable=false)
private SubRegionEntity subRegion;
but when I try to run
select c from CragEntity c where c.subRegion.region = :area
I get an exception
java.lang.RuntimeException: org.hibernate.QueryException: could
not resolve property: subRegion of: uk.co.bmc.rad.dal.CragEntity
Hopefully this is possible and I'm being slow...
Many thanks in advance for any help!
In your query you are searching for the property "subRegion" though in your entity definition you have the name "fkSubRegionId", so you must change the var name or the query. ;)
EDIT: Sorry i misreaded the relation.
Can you access the property (without making an HQL query) with the relationship inside the code?
Unless, you want to pick only certain fields in your query I would recommend a query like:
from CragEntity c where c.subRegion.region='theRegion'
It turns out there were several issues - one conceptual, one with how IntelliJ had generated a relationship I was copying and one between the chair and keyboard...
IntelliJ had picked the region to subregion relationship with the owner at the "wrong" end - probably a schema issue rather than IntelliJ's fault. Once I realised that and figured out the fix I could copy that to CragEntity and SubRegionEntity
In CragEntity I added:
private SubRegionEntity subRegion;
#ManyToOne
#JoinColumn(name="fk_SubRegionId",nullable=false)
public SubRegionEntity getSubRegion() {
return subRegion;
}
public void setSubRegion(SubRegionEntity subRegion) {
this.subRegion = subRegion;
}
and then in SubRegionEntity I added:
private List<CragEntity> crags;
#OneToMany(mappedBy = "subRegion")
List<CragEntity> getCrags() {
return crags;
}
public void setCrags(List<CragEntity> crags) {
this.crags = crags;
}
Also, it seem that any entity class that is going to be one end of a relationship has to implement serializable (I guess the entities get serialized into the owner. So that needed adding onto SubRegionEntity and RegionEntity
The silliness on my part was of course that the query should have been c.subRegion.region.name otherwise I was comparing an object of type RegionEntity with a string... doh - very stupid mistake on my part.
I'm new to TDD but as always as soon as I wrote tests for what I thought should be happening with the existing code I was walked through my errors (and given google keywords by the exceptions and errors :-))
I'm trying to map two objects to each other using a ManyToMany association, but for some reason when I use the mappedBy property, hibernate seems to be getting confused about exactly what I am mapping. The only odd thing about my mapping here is that the association is not done on a primary key field in one of the entries (the field is unique though).
The tables are:
Sequence (
id NUMBER,
reference VARCHAR,
)
Project (
id NUMBER
)
Sequence_Project (
proj_id number references Project(id),
reference varchar references Sequence(reference)
)
The objects look like (annotations are on the getter, put them on fields to condense a bit):
class Sequence {
#Id
private int id;
private String reference;
#ManyToMany(mappedBy="sequences")
private List<Project> projects;
}
And the owning side:
class Project {
#Id
private int id;
#ManyToMany
#JoinTable(name="sequence_project",
joinColumns=#JoinColumn(name="id"),
inverseJoinColumns=#JoinColumn(name="reference",
referencedColumnName="reference"))
private List<Sequence> sequences;
}
This fails with a MappingException:
property-ref [_test_local_entities_Project_sequences] not found on entity [test.local.entities.Project]
It seems to weirdly prepend the fully qualified class name, divided by underscores. How can I avoid this from happening?
EDIT:
I played around with this a bit more. Changing the name of the mappedBy property throws a different exception, namely:
org.hibernate.AnnotationException: mappedBy reference an unknown target entity property: test.local.entities.Project.sequences
So the annotation is processing correctly, but somehow the property reference isn't correctly added to Hibernate's internal configuration.
I have done the same scenario proposed by your question. And, as expected, i get the same exception. Just as complementary task, i have done the same scenario but with one-to-many many-to-one by using a non-primary key as joined column such as reference. I get now
SecondaryTable JoinColumn cannot reference a non primary key
Well, can it be a bug ??? Well, yes (and your workaround works fine (+1)). If you want to use a non-primary key as primary key, you must make sure it is unique. Maybe it explains why Hibernate does not allow to use non-primary key as primary key (Unaware users can get unexpected behaviors).
If you want to use the same mapping, You can split your #ManyToMany relationship into #OneToMany-ManyToOne By using encapsulation, you do not need to worry about your joined class
Project
#Entity
public class Project implements Serializable {
#Id
#GeneratedValue
private Integer id;
#OneToMany(mappedBy="project")
private List<ProjectSequence> projectSequenceList = new ArrayList<ProjectSequence>();
#Transient
private List<Sequence> sequenceList = null;
// getters and setters
public void addSequence(Sequence sequence) {
projectSequenceList.add(new ProjectSequence(new ProjectSequence.ProjectSequenceId(id, sequence.getReference())));
}
public List<Sequence> getSequenceList() {
if(sequenceList != null)
return sequenceList;
sequenceList = new ArrayList<Sequence>();
for (ProjectSequence projectSequence : projectSequenceList)
sequenceList.add(projectSequence.getSequence());
return sequenceList;
}
}
Sequence
#Entity
public class Sequence implements Serializable {
#Id
private Integer id;
private String reference;
#OneToMany(mappedBy="sequence")
private List<ProjectSequence> projectSequenceList = new ArrayList<ProjectSequence>();
#Transient
private List<Project> projectList = null;
// getters and setters
public void addProject(Project project) {
projectSequenceList.add(new ProjectSequence(new ProjectSequence.ProjectSequenceId(project.getId(), reference)));
}
public List<Project> getProjectList() {
if(projectList != null)
return projectList;
projectList = new ArrayList<Project>();
for (ProjectSequence projectSequence : projectSequenceList)
projectList.add(projectSequence.getProject());
return projectList;
}
}
ProjectSequence
#Entity
public class ProjectSequence {
#EmbeddedId
private ProjectSequenceId projectSequenceId;
#ManyToOne
#JoinColumn(name="ID", insertable=false, updatable=false)
private Project project;
#ManyToOne
#JoinColumn(name="REFERENCE", referencedColumnName="REFERENCE", insertable=false, updatable=false)
private Sequence sequence;
public ProjectSequence() {}
public ProjectSequence(ProjectSequenceId projectSequenceId) {
this.projectSequenceId = projectSequenceId;
}
// getters and setters
#Embeddable
public static class ProjectSequenceId implements Serializable {
#Column(name="ID", updatable=false)
private Integer projectId;
#Column(name="REFERENCE", updatable=false)
private String reference;
public ProjectSequenceId() {}
public ProjectSequenceId(Integer projectId, String reference) {
this.projectId = projectId;
this.reference = reference;
}
#Override
public boolean equals(Object o) {
if (!(o instanceof ProjectSequenceId))
return false;
final ProjectSequenceId other = (ProjectSequenceId) o;
return new EqualsBuilder().append(getProjectId(), other.getProjectId())
.append(getReference(), other.getReference())
.isEquals();
}
#Override
public int hashCode() {
return new HashCodeBuilder().append(getProjectId())
.append(getReference())
.hashCode();
}
}
}
I finally figured it out, more or less. I think this is basically a hibernate bug.
edit: I tried to fix it by changing the owning side of the association:
class Sequence {
#Id
private int id;
private String reference;
#ManyToMany
#JoinTable(name="sequence_project",
inverseJoinColumns=#JoinColumn(name="id"),
joinColumns=#JoinColumn(name="reference",
referencedColumnName="reference"))
private List<Project> projects;
}
class Project {
#Id
private int id;
#ManyToMany(mappedBy="projects")
private List<Sequence> sequences;
}
This worked but caused problems elsewhere (see comment). So I gave up and modeled the association as an entity with many-to-one associations in Sequence and Project. I think this is at the very least a documentation/fault handling bug (the exception isn't very pertinent, and the failure mode is just wrong) and will try to report it to the Hibernate devs.
IMHO what you are trying to achieve is not possible with JPA/Hibernate annotations. Unfortunately, the APIDoc of JoinTable is a bit unclear here, but all the examples I found use primary keys when mapping join tables.
We had the same issue like you in a project where we also could not change the legacy database schema. The only viable option there was to dump Hibernate and use MyBatis (http://www.mybatis.org) where you have the full flexibility of native SQL to express more complex join conditions.
I run into this problem a dozen times now and the only workaround i found is doing the configuration of the #JoinTable twice with swapped columns on the other side of the relation:
class Sequence {
#Id
private int id;
private String reference;
#ManyToMany
#JoinTable(
name = "sequence_project",
joinColumns = #JoinColumn(name="reference", referencedColumnName="reference"),
inverseJoinColumns = #JoinColumn(name="id")
)
private List<Project> projects;
}
class Project {
#Id
private int id;
#ManyToMany
#JoinTable(
name = "sequence_project",
joinColumns = #JoinColumn(name="id"),
inverseJoinColumns = #JoinColumn(name="reference", referencedColumnName="reference")
)
private List<Sequence> sequences;
}
I did not yet tried it with a column different from the primary key.