i'm new at JPA and need some advice.
I have two tables, Car and Driver linked as ManyTyOne. And I would obtain Car entity with info about several drivers. Now i can get from Driver only driver_id, it looks like this, but need to receive also drivers name and lastName.
Class Car:
#Entity
public class Car {
#JsonIgnoreProperties({"telephone", "mail",})
#ManyToOne
#JoinColumn(name = "driver_id"),
private Driver driver;
...
}
#Entity
class Driver:
#JsonIgnoreProperties({"telephone", "mail",})
public class Driver {
private Long id;
private String firstName;
private String lastName;
private String telephone;
private String mail;
...
}
Table car SQL:
CREATE TABLE `car` (
`id` decimal(20) unsigned NOT NULL AUTO_INCREMENT,
`driver_id` bigint(20) DEFAULT NULL,
PRIMARY KEY (`id`),
FOREIGN KEY (driver_id) REFERENCES driver(id),
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
At first I think that it's possible to receive also drivers name and surname the next way:
#JoinColumns({#JoinColumn(name = "driver_id"),
#JoinColumn(name = "first_name"),
#JoinColumn(name = "last_name")})
But documentation says, that #JoinColums is sutable only for composite fk.
Please give me a hint, how can i do whats needed.
Assuming your Driver class is an entity (you didn't put in the #Entity annotation in the above code.)
Your current mapping is saying that each driver can drive multiple cars. Since the many to one only exists on the Car side, there's no way to go from Driver to Car. To do that, you would need to have a #OneToMany mapping going from Driver to Car. (Also, shouldn't this be a many to many mapping? each Driver can drive multiple cars. and each car can have multiple drivers?)
In any case, given the mapping as above, you should be able to access driver.firstName and driver.lastName. What is the error when you are attempting to do that?
Related
I created an entity/table for a book, and I want to achieve that each element can reference another book to create a series.
I came up with this:
#Entity
public class Book {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer bookId;
#Lob
private String text;
#OneToOne
#JoinColumn(name = "book_id")
private Book previousPart;
}
However, the attribute previousPart is not seen as a column in my Database, while the others are. Is there a different annotation I have to use or is this the wrong way to model a relationship like this? Or do I have to use the type Integer instead of Book directly (I thought this was what the framework does internally)?
Try this way:
#OneToOne
#JoinColumn
private Book previousPart;
In your code you defined the book_id field as the join-column, which is an already existing column (the id itself), so actually you linked all entries to themselves.
I'm new to Stackoverflow, so I will make my best to conforms with usage. I was wondering if there were a way to get a complete list of changes/snapshots of a given Entity. For now it works well with edition of Singular Properties, as well as Addition and Deletion to Collection Property. But I'm unable to find when a Child Entity in the Collection Property was updated.
Given two Entities, and a LinkEntity:
#Entity
class Person {
#Id
Long id;
#OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
Set<LinkAddress> addresses;
}
#Entity
class Address {
#Id
Long id;
#OneToMany(mappedBy = "address")
Set<Address> persons;
}
#Entity
class LinkPersonAddress {
#Id
Long id;
#ManyToOne
#ShallowReference
Person person;
#ManyToOne
#ShallowReference
Address address;
String linkType;
}
My use case is following. I get a specific Person by Id #1, and then mutate the type of specific Address (ie. HOME --> WORK). I save the Person back with the modified Set and let JPA Cascade my changes. Although all Spring Data Repositories for Person, Address, and LinkPersonAddress are annotated with #JaversSpringDataAuditable, I cannot retrieve this "update" using Javers QueryBuilder with the class Person and Id #1. It makes sense as I should query the class LinkPersonAddress instead, but how can I specify that I want only the changes from LinkPersonAddress relevant to Person with Id #1.
PS: Please apologize any typos in code snippets, as I didn't write it in my Dev Environment.
Let's start from the mapping. You did it wrong, Address is a classical ValueObject (see https://javers.org/documentation/domain-configuration/#value-object) not Entity. Because:
Address doesn't have its own identity (primary key genereted by a db sequence doesn't count)
Address is owned by the Person Entity. Person with its Addresses forms the Aggregate.
When you correct the mapping, you can use ChildValueObjects filter, see https://javers.org/documentation/jql-examples/#child-value-objects-filter
I have an entity class that is simply a ManyToMany with extra column, as follows:
#Entity
#Table(name = "view_templates_device_types")
public class ViewTemplateDeviceTypeEntity implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#ManyToOne
#JoinColumn(name = "view_template_id")
private ViewTemplateEntity viewTemplate;
#Id
#ManyToOne
#JoinColumn(name = "device_type_id")
private DeviceTypeEntity deviceType;
#Column(name = "priority", nullable = false)
private int priority;
public ViewTemplateDeviceTypeEntity() {
}
...
}
I noticed that when I create a new object of this type, set viewTemplate and deviceType to values that have corresponding data in the db and I call entityManager.persist(entity) the data is stored. But when I call entityManager.merge(entity) instead of persist I get an exception:
SQL Error: 1048, SQLState: 23000
Column 'view_template_id' cannot be null
I thought that calling merge should result with data inserted into database in case it is not stored yet. It is quite important to me to use merge here (because of cascades). What can I do to make it work?
As per the JPA spec, section 2.4
"A composite primary key must correspond to either a single persistent field or property or to a set of such fields or properties as described below. A primary key class must be defined to represent a composite primary key. Composite primary keys typically arise when mapping from legacy databases when the database key is comprised of several columns. The EmbeddedId or IdClass annotation is used to denote a composite primary key. See Sections 11.1.17 and 11.1.22.".
So you either need #IdClass or #EmbeddedId. Anything else is non-portable and prone to error. I am very surprised of any JPA provider that does not throw out warnings for this.
I'm trying to use entities with a MySQL ndbcluster table. This table type doesn't allow foreign keys, but up until now it hasn't been a problem with my entities.
However, I have run into a bit of a problem, when I try to load an entity using the EntityManager's createNativeQuery method. I need to use this method due to my inability to do this: How to make a CriteriaBuilder join with a custom "on" condition?
My MySQL table looks like this:
CREATE TABLE `category` (
`id` SMALLINT(6) NOT NULL AUTO_INCREMENT,
`category_id` SMALLINT(6) NULL DEFAULT NULL,
PRIMARY KEY (`id`),
INDEX `category_id` (`category_id`)
)
COLLATE='utf8_general_ci'
ENGINE=ndbcluster
ROW_FORMAT=DEFAULT
If I change the table engine to innodb, and add foreign keys, the createNativeQuery method works fine.
My entity class looks like this:
#Entity
#Table(name = "category")
public class Category implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "id")
private Short id;
#OneToMany(mappedBy = "categoryId")
private List<Category> categoryList;
#JoinColumn(name = "category_id", referencedColumnName = "id")
#ManyToOne
private Category categoryId;
public Category() {
}
// getters and setters
}
Even without foreign keys, this entity works fine when I use the CriteriaBuilder for a query, but unfortunately not everything is possible with the CriteriaBuilder.
I get an error when I call getResultList on a Query object created with createNativeQuery. I don't know if this is a bug, or if something should be added to my entity class to make this work.
The error says:
Exception [EclipseLink-6044] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.QueryException
Exception Description: The primary key read from the row [ArrayRecord(
=> 2519
=> 2463
=> Tools)] during the execution of the query was detected to be null. Primary keys must not contain null.
Query: ReadAllQuery(referenceClass=Category sql="select * from `category`")
at org.eclipse.persistence.exceptions.QueryException.nullPrimaryKeyInBuildingObject(QueryException.java:895)
at org.eclipse.persistence.internal.descriptors.ObjectBuilder.buildObject(ObjectBuilder.java:584)
at org.eclipse.persistence.internal.descriptors.ObjectBuilder.buildObject(ObjectBuilder.java:560)
at org.eclipse.persistence.queries.ObjectLevelReadQuery.buildObject(ObjectLevelReadQuery.java:717)
at org.eclipse.persistence.queries.ReadAllQuery.registerResultInUnitOfWork(ReadAllQuery.java:769)
...
My table contains 1 row, where id=1 and category_id=null, so there are no primary keys with a null-value, despite what the error says. If I remove that row or set category_id=1, I don't get an error.
Need help, please.
Managed to make it work by switching from EclipseLink (JPA 2.0) to OpenJPA (JPA 2.0). Seems like there is a bug somewhere in EclipseLink 2.3.2 and/or GlassFish 3.1.2.2.
I've used EclipseLink (JPA 2.0) in another project of mine, using a slightly different version Netbeans + GlassFish 3.1.1, where I used createNativeQuery on an entity class for a non-relational myisam table. This never caused any problem. It really must be a bug.
But problem solved. Bye, bye EclipseLink, hello OpenJPA.
The issue is case sensitivity. In MySQL your column "id" will be defined in the database as "ID" unless you quote it. If you switch your mappings to upper case it should fix the issue (i.e. "ID").
You could also quote the column name ("'id'")
or set the persistence unit property,
"eclipselink.jpa.uppercase-column-names"="true"
I am using JPA in my application. In one of the table, I have not used primary key (I know its a bad design).
Now the generated entity is as mentioned below :
#Entity
#Table(name="INTI_SCHEME_TOKEN")
public class IntiSchemeToken implements Serializable {
private static final long serialVersionUID = 1L;
#Column(name="CREATED_BY")
private String createdBy;
#Temporal( TemporalType.DATE)
#Column(name="CREATED_ON")
private Date createdOn;
#Column(name="SCH_ID")
private BigDecimal schId;
#Column(name="TOKEN_ID")
private BigDecimal tokenId;
public IntiSchemeToken() {
}
public String getCreatedBy() {
return this.createdBy;
}
public void setCreatedBy(String createdBy) {
this.createdBy = createdBy;
}
public Date getCreatedOn() {
return this.createdOn;
}
public void setCreatedOn(Date createdOn) {
this.createdOn = createdOn;
}
public BigDecimal getSchId() {
return this.schId;
}
public void setSchId(BigDecimal schId) {
this.schId = schId;
}
public BigDecimal getTokenId() {
return this.tokenId;
}
public void setTokenId(BigDecimal tokenId) {
this.tokenId = tokenId;
}
}
Here In my project, eclipse IDE shows ERROR mark(RED colored cross) on this class and the error is "The entity has no primary key attribute defined".
Can anyone tell me, How to create an entity without primary key ?
Thanks.
You can't. An entity MUST have a unique, immutable ID. It doesn't have to be defined as a primary key in the database, but the field or set of fields must uniquely identify the row, and its value may not change.
So, if one field in your entity, or one set of fields in your entity, satisfies these criteria, make it (or them) the ID of the entity. For example, if there is no way that a user can create two instances in the same day, you could make [createdOn, createdBy] the ID of the entity.
Of course this is a bad solution, and you should really change your schema and add an autogenerated, single-column ID in the entity.
If your Primary Key(PK) is a managed super class which is inherited in an entity class then you will have to include the mapped super class name in the persistence.xml file.
Look at the bug report:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=361042
If you need to define a class without primary key, then you should mark that class as an Embeddable class. Otherwise you should give the primary key for all entities you are defining.
You can turn off (change) validation that was added.
Go to workspace preferences 'Java Persistence->JPA->Errors/Warnings' next 'Type' and change 'Entity has no primary key' to 'Warnning'.
In addition to http://en.wikibooks.org/wiki/Java_Persistence/Identity_and_Sequencing#No_Primary_Key you can use some build-in columns like ROWID in Oracle:
Oracle legacy table without good PK: How to Hibernate?
but with care:
http://www.orafaq.com/wiki/ROWID
Entity frameworks doesn't work for all kind of data (like statistical data which was used for analysis not for querying).
Another solution without Hibernate
If
- you don't have PK on the table
- there is a logical combination of columns that could be PK (not necessary if you can use some kind of rowid)
-- but some of the columns are NULLable so you really can't create PK because of DB limitation
- and you can't modify the table structure (would break insert/select statements with no explicitly listed columns at legacy code)
then you can try the following trick
- create view at database with virtual column that has value of concatenated logical key columns ('A='||a||'B='||'C='c..) or rowid
- create your JPA entity class by this view
- mark the virtual column with #Id annotation
That's it. Update/delete data operations are also possible (not insert) but I wouldn't use them if the virtual key column is not made of rowid (to avoid full scan searches by the DB table)
P.S. The same idea is partly described at the linked question.
You need to create primary key ,If not found any eligible field then create auto increment Id.
CREATE TABLE fin_home_loan (
ID int NOT NULL AUTO_INCREMENT,
PRIMARY KEY (ID));
Just add fake id field.
In Postgres:
#Id
#Column(name="ctid")
String id;
In Oracle:
#Id
#Column(name="ROWID")
String rowid;