I am using JPA annotations and when i have relation OneToMany - ManyToOne, when i see my entity in the ManyToOne, the joinColumn is always with null value.
Next i will show my example, i have Product:
#Entity
#Table(name = "PC_PRODUCT")
public class Product extends LaunchEntity {
private static final long serialVersionUID = 1L;
#XmlElement(name = "Product_Name", required = true)
protected String productName;
#XmlElement(name = "Product_Description")
protected String productDescription;
#XmlElement(name = "Product_To_Charge")
#OneToMany(mappedBy = "product", cascade=CascadeType.MERGE)
protected List<ChargeRelation> productToCharge;
And, this is my ChargeRelation class:
#Entity
#Table(name="PC_CHARGE_RELATION")
public class ChargeRelation
extends RelationEntity
{
private static final long serialVersionUID = 1L;
#XmlElement(name = "Charge", required = true)
#OneToOne(cascade = CascadeType.MERGE)
protected Charge charge;
#XmlTransient
#ManyToOne(cascade=CascadeType.MERGE)
#JoinColumn(name="PRODUCT_ID")
protected Product product;
I am reading a xml file, convert data for a string, make unmarshall for my root object and persist this object.
The problem is when i found a charge relation in my string, the values are inserted on the charge relation table but the column with the product_id is always null.
I have all setters and getters defined. How i can force this to make the manual insert? thanks
Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB 2 (JSR-222) expert group.
EclipseLink JAXB (MOXy) has an extension called #XmlInverseReference that allows you to map the back-pointer.
Product
#Entity
#Table(name = "PC_PRODUCT")
public class Product extends LaunchEntity {
#XmlElement(name = "Product_To_Charge")
#OneToMany(mappedBy = "product", cascade=CascadeType.MERGE)
protected List<ChargeRelation> productToCharge;
}
ChargeRelation
The #XmlInverseReference annotation is used where you previously had #XmlTransient. #XmlInverseReference acts like #XmlTransient during the marshal operation, and will populate the back-pointer during an unmarshal operation.
#Entity
#Table(name="PC_CHARGE_RELATION")
public class ChargeRelation extends RelationEntity {
#XmlInverseReference(mappedBy = "productToCharge")
#ManyToOne(cascade=CascadeType.MERGE)
#JoinColumn(name="PRODUCT_ID")
protected Product product;
}
For More Information
http://blog.bdoughan.com/2010/07/jpa-entities-to-xml-bidirectional.html
http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html
Note that JPA provider reflects the state of many-to-one side of relationship when saving it to the database.
However, JAXB only populates one-to-many side during XML unmarshalling, therefore you need to populate many-to-one side manually after unmarshalling.
Related
Mongodb is a no-schema document database, but in spring data, it's necessary to define entity class and repository class, like following:
Entity class:
#Document(collection = "users")
public class User implements UserDetails {
#Id private String userId;
#NotNull #Indexed(unique = true) private String username;
#NotNull private String password;
#NotNull private String name;
#NotNull private String email;
}
Repository class:
public interface UserRepository extends MongoRepository<User, String> {
User findByUsername(String username);
}
Is there anyway to use map not class in spring data mongodb so that the server can accept any dynamic JSON data then store it in BSON without any pre-class define?
First, a few insightful links about schemaless data:
what does “schemaless” even mean anyway?
“schemaless” doesn't mean “schemafree”
Second... one may wonder if Spring, or Java, is the right solution for your problem - why not a more dynamic tool, such a Ruby, Python or the Mongoshell?
That being said, let's focus on the technical issue.
If your goal is only to store random data, you could basically just define your own controller and use the MongoDB Java Driver directly.
If you really insist on having no predefined schema for your domain object class, use this:
#Document(collection = "users")
public class User implements UserDetails {
#Id
private String id;
private Map<String, Object> schemalessData;
// getters/setters omitted
}
Basically it gives you a container in which you can put whatever you want, but watch out for serialization/deserialization issues (this may become tricky if you had ObjectIds and DBRefs in your nested document). Also, updating data may become nasty if your data hierarchy becomes too complex.
Still, at some point, you'll realize your data indeed has a schema that can be pinpointed and put into well-defined POJOs.
Update
A late update since people still happen to read this post in 2020: the Jackson annotations JsonAnyGetter and JsonAnySetter let you hide the root of the schemaless-data container so your unknown fields can be sent as top-level fields in your payload. They will still be stored nested in your MongoDB document, but will appear as top-level fields when the ressource is requested through Spring.
#Document(collection = "users")
public class User implements UserDetails {
#Id
private String id;
// add all other expected fields (getters/setters omitted)
private String foo;
private String bar;
// a container for all unexpected fields
private Map<String, Object> schemalessData;
#JsonAnySetter
public void add(String key, Object value) {
if (null == schemalessData) {
schemalessData = new HashMap<>();
}
schemalessData.put(key, value);
}
#JsonAnyGetter
public Map<String, Object> get() {
return schemalessData;
}
// getters/setters omitted
}
I have an entity called ReferenceForm which contains an AutoPopulatingList of ReferenceItems. It looks like this:
#Entity
public class ReferenceForm implements Serializable{
private static final long serialVersionUID = -5633788166190438576L;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
long id;
#lob
private AutoPopulatingList<ReferenceItem> referenceItems;
}
If I add no annotation at all to the AutoPopulatingList, the field type which hibernate creates is varbinary(255). This causes string truncation errors. To work around this, I used the #lob annotation. This felt questionable at the time, but it worked fine. At this point I was just using HSQLDB.
Now the application needs to run against MSSQL. I have generated the schema using Hibernate, and referenceItems ia an image column on the ReferenceForm table. The items themselves are stored in the ReferenceItem table.
Is #lob an appropriate annotation here?.
EDIT: ReferenceItem looks like this:
#Entity
public class ReferenceItem implements Serializable {
private static final long serialVersionUID = -9077063073733429102L;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
long id;
private Title title;
private String firstName;
private String surname;
private String positionHeld;
private String institutionCompany;
#Embedded
private Address address;
#Embedded
private Telephone telephone;
private String email;
private boolean existingReference;
private String fileName;
public ReferenceItem() {
}
...getters and setters
}
SECOND EDIT:
Thanks to Willome for suggesting using #OneToMany. In the end, this is what worked.
//from
#lob
private AutoPopulatingList<ReferenceItem> referenceItems;
//to
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private List<ReferenceItem> referenceItems = new AutoPopulatingList<ReferenceItem>(ReferenceItem.class);
#OneToMany accurately describes the nature of the relationship
Use the interface (List) instead of the implementation when defining the field. See http://docs.jboss.org/hibernate/core/3.3/reference/en/html/collections.html
Define the CascadeType, otherwise this error appears on saving the entity: org.hibernate.TransientObjectException: object references an unsaved transient instance
Make the FetchType EAGER otherwise you cannot load the form in a different transaction: this error appears: failed to lazily initialize a collection of role: ReferenceForm.referenceItems, could not initialize proxy - no Session
You should replace your #Lob annonation with a #OneToMany and replace the AutoPopulatingList with a collection-valued field declared as an interface type (Check out the topic 6.1. Persistent collections on this link http://docs.jboss.org/hibernate/core/3.3/reference/en/html/collections.html.)
//#Lob
#OneToMany(mappedBy = "referenceForm")
private AutoPopulatingList<ReferenceItem> referenceItems; //fail AutoPopulatingList is not an interface
#OneToMany(mappedBy = "referenceForm")
private Set<ReferenceItem> referenceItems; // OK with Set/Collection/List
Thanks to Willome for suggesting using #OneToMany. In the end, this is what worked.
//from
#lob
private AutoPopulatingList<ReferenceItem> referenceItems;
//to
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private List<ReferenceItem> referenceItems = new AutoPopulatingList<ReferenceItem>(ReferenceItem.class);
#OneToMany accurately describes the nature of the relationship
Use the interface (List) instead of the implementation when defining
the field. See
http://docs.jboss.org/hibernate/core/3.3/reference/en/html/collections.html
Define the CascadeType, otherwise this error appears on saving the
entity: org.hibernate.TransientObjectException: object references an
unsaved transient instance
Make the FetchType EAGER otherwise you
cannot load the form in a different transaction: this error appears:
failed to lazily initialize a collection of role:
ReferenceForm.referenceItems, could not initialize proxy - no Session
I am totally new at this, I am sorry if it is stupid question.
I am trying to design database model for Google App Engine in JPA, but I am unable to get it right. When I find the way I can't get annotations right or I am getting error about M:N not supported in Google App Engine.
I need entity user to have multiple groups and groups have multiple users and there are users who are also group admins.
My basic model was User -> usergroup(user; group; (bool)isAdmin) <-Group
Can somebody give a clean and simple example of how to define relationships?
Please try this.
#Entity
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Key id;
private String name;
#ManyToOne(fetch = FetchType.LAZY)
private UserGroup usergroup;
}
class userGroup
#Entity
public class UserGroup {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Key id;
private String name;
private boolean admin;
#OneToMany(mappedBy = "usergroup", cascade = CascadeType.ALL)
private List<User> users = new ArrayList<User>();
}
please be noticed GAE have limitation on JPA you can read more here
I don't know anything about Google App Engine, but I can help with JPA though.
The problem here is the "isAdmin" column, which prevents the data model to be a simple #ManyToMany relationship with a joiner table.
With the introduction of this field, in the data model you need a Map on the User entity with key=Group and value=isAdmin, similarly you need a corresponding Map in the Group entity in order to know if each User is an admin.
This is modeled with #ElementCollection in the following way:
#Entity
#Table(name="User")
public class User
{
#Id
#GeneratedValue(strategy= GenerationType.TABLE)
private int id;
private String name;
#ElementCollection
#CollectionTable(name="Users_Groups", joinColumns={#JoinColumn(name="userId")})
#MapKeyJoinColumn(name="groupId")
#Column(name="isAdmin")
private Map<Group, Boolean> groups;
}
#Entity
#Table(name="Group")
public class Group
{
#Id
#GeneratedValue(strategy= GenerationType.TABLE)
private int id;
private String name;
#ElementCollection
#CollectionTable(name="Users_Groups", joinColumns={#JoinColumn(name="groupId")})
#MapKeyJoinColumn(name="userId", insertable=false, updatable=false)
#Column(name="isAdmin", insertable=false, updatable=false)
private Map<User, Boolean> users;
}
The important annotation is #ElementCollection, the other annotations are just to name the specific columns of the collection table and make sure they match from both entities: #CollectionTable gives the name of the table and the name of the column representing the id in the current entity. #MapKeyJoinColumn gives the name of the column representing the id of the "key" element in the Map, and #Column gives the name of the "value" element in the map.
I'm not sure if the insertable=false and updatable=false are needed in one of the entities, might avoid adding duplicate rows due to the cyclic dependency between User and Group.
Also you need to manually create the collection table, because at least EclipseLink tries to create it with two "groupId" and "isAdmin" columns. You might consider reviewing the design if it is absolutely needed a cyclic dependency between User and Group.
I am currently working with GWT, GAE and using JPA as my ORM. I have an issue where the keys that GAE is generating are too large reasonably to be used on a mobile device with RequestFactory. The amount of data in a small list is overwhelming due to the size of the ID/KEY when converted to String.
I am using String for my key's so that I can handle inheritence.
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
protected String key;
This creates a key that is very long example "agxzbWFydGJhcnNpdGVyFAsSDUVzdGFibGlzaG1lbnQYuAIM" and gets larger due to storing object type and parent in the key.
I need a way to create a smaller unique id but still have the ability to handle inheritence in GAE. I tried Long as the #Id/key but was not able to use a #OneToMany relationship on my objects due to the relationship that is built into the String/Key key.
The other option is to create a sequence for each class and use a Long property for that id. There is an example below but I am not sure how to handle a generated Long sequence in app engine.
#GeneratedValue
private Long friendlyClassSpecificKey;
Any advice would be appreciated. If there is another option other than using the sequence for each class type I am interested but if not is there an example of creating a sequence (That is not the #ID) for a specific class?
I came up with a good solution for smaller keys. I think the best way to do this cleanly is to use jpa/jdo 2 for app engine with an unowned relationship. This way you can fetch the keys from (Long) id using just their type and not have to use the parent relationship.
This is the base datstore object and notice I am using the app engine key.
#Entity
#Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class DatastoreObject {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Key key;
public Long getId() {
return key.getId();
}
}
This class will use the #Unowned attribute supported in jpa 2 so that the inventory's key does not contain the parent establishment key. Otherwise you would have to pass the parent id in also and resolve that to a key based on type. This is because in an owned relationship the child key contains the parent key also.
#Entity
public class Establishment extends DatastoreObject {
#Unowned
#OneToOne(cascade = CascadeType.ALL)
private Inventory inventory;
}
Then in my dao base class I use the class
public class DaoBase<T extends DatastoreObject> {
protected Class<T> clazz;
#SuppressWarnings("unchecked")
public DaoBase() {
clazz = (Class<T>) ((ParameterizedType) getClass()
.getGenericSuperclass()).getActualTypeArguments()[0];
}
/**
* Find an object by it's shortened long id
* #param id
* #return
* #throws EntityNotFoundException
*/
public T find(Long id) {
if (id == null) {
return null;
}
EntityManager em = ThreadLocalPersistenceManager.getEntityManager();
Key key = getKey(id);
T obj = em.find(clazz, key);
return obj;
}
protected Key getKey(Long id) {
return KeyFactory.createKey(clazz.getSimpleName(), id);
}
}
I'm getting into problems with JPA. I'm trying to implement a database that allows users to follow other users and be followed.
I think I'd need (summing up) something like this:
USER_TABLE: id | userName
RELATIONSHIP_TABLE: id | follower | followed | acceptation
I have two entities (also summed up):
#Entity
public class User implements Serializable {
#Id
private Long id;
private String userName;
#OneToMany
private Collection<Relationship> followings;
}
#Entity
public class Relationship implements Serializable {
#Id
private Long id;
private User follower;
private User followed;
private boolean accepted;
}
My problem is that I'm not sure if it's possible to do this, because I obtain more tables that the two that I need.
Can anybody help me?
Thanks and sorry about my english.
You obtain more tables because you did not make the associations bidirectional. JPA has no way to know that Relationship.follower is the other side of the User.followings if you don't tell:
#Entity
public class User implements Serializable {
#OneToMany(mappedBy = "follower")
private Collection<Relationship> followings;
// ...
}
#Entity
public class Relationship implements Serializable {
#ManyToOne
#JoinColumn(name = "follower")
private User follower;
#ManyToOne
#JoinColumn(name = "followed")
private User followed;
// ...
}
The documentation of course explains how that works.