My spring boot project uses an existing database, I have a new model entity/table in my project that must have a foreign key constraint with an existing table in the database.
I've tried to find solution online but all the answers are for the case where both the tables are present as entities in that project and using some #ManyToOne, #OneToMany annotations.
I can't define those annotations because I don't have the reference table as an entity or model in my project.
Let's say I have class like:
#Entity(name = "user")
public class User {
#Id
#GeneratedValue
private long userId;
private long departmentId;
I want to put a foreign key contraint on the departmentId column to reference to id column of the existing department table that isn't defined as a model or entity in my project.
Thanks
Just do it as normal
example
#Column(name = "department_id")
private Department departmentId;
You can later access it Department.departmentId. Hope this helps.
Try it like this
#ManyToOne
#JoinColumn(name="(column name of current entity)", referencedColumnName="(column name in target entity)")
private Department departmentId;
you can skip the referencedColumnName if the column name is same in both the entities
Related
It should be easy. Oracle has defined "generate always" for an id column. So there is no need to add this id to the insert statement. How do i define my entity that it is handling right.
#Entity
public class Example {
#Id
#GeneratedValue // if i remove this annotation than hibernate complains that i need to set it manually
#Column(name="ID", insertable=false, updatable=false)
private Long id;
}
in the error message i see that it still tries to add the id to the query.
My work-around for the column. Add the #id to an other column and remove the id column from entity definition :-D
I am trying to create new table and join with ManyToOne relation with my existing table
below is my implementation
New table
#Entity(name="request_city_id")
#Table(uniqueConstraints={#UniqueConstraints{columnNames={"request_id","cityId"})})
#Data
#NoArgsConstructor
#FieldDefault(level=AccessLevel.PRIVATE)
public class RequestCityId{
#GenratedValue(strategy=SEQUENCE, generator="seq_req_city_id")
#SequenceGenerator(name="seq_req_city_id", allocationSize=1)
#Column(name="rc_id")
#Id
long id;
#ManyToOne
#JoinColumn(name="request_id")
Request request;
String cityId;
String status
}
Existing table
#Entity(name="request")
#Data
#NoArgsConstructor
#FieldDefault(level=AccessLevel.PRIVATE)
public class Request{
String frequency
#GenratedValue(strategy=SEQUENCE, generator="seq_req_d")
#SequenceGenerator(name="seq_req_id", allocationSize=1)
#Column(name="request_id")
#Id
long id;
#OneToMany(cascade={ PERSIST, MERGE}, mappedBy="request", fetch=EAGER)
Set<RequestCityId> requestCityIds;
}
but when I am trying to insert into my new table I see my hibernate query gets stuck and just gets timed out after sometime, I am not sure what I am doing wrong here? If I just kep cascade type MERGE then getting
Hibernate Error: a different object with the same identifier value was already associated with the session
First you should create an getters and setters method to each entity.
Request Class
Request City Id Class
this code creates the tables and also saves the data into the table.
Using #Data in entity classes in not recommended because it may cause some problems with jpa as mentioned here.
Is it possible to Greate DDL using JPA with bidirectional mapping and without foreign key? If can, is it best practice?
#Entity
class Book{
int id;
String title;
#OneToMany(mappedBy="book")
Set<BookDetail> book_detail;
}
#Entity
class BookDetail{
int id;
String name;
String description;
#ManyToOne
Book book;
}
Yes. It is possible using a join table. It will have foreign keys of course.
#Entity
class Book{
#OneToMany
List<BookDetail> bookDetail;
}
#Entity
class BookDetail{
#ManyToOne(fetch = FetchType.LAZY)
Book book;
}
what is #JoinColumn and how it is used in Hibernate
You can't do it without at least one foreign key, since a DB needs to establish some connection between two entities - BookDetail and Book. It is possible to create two tables for these entities without a real foreign key by using plain integer attribute in BookDetail which will be storing a value of Book's id. But don't do that!
With a foreign key your DBMS generates constraints so it's known about the relationship and it prevents some unsafe deletions and insertions, so each BookDetail's row references existing Books one.
Without real foreign key you c accidentally remove a Book and you BookItem's
I have two entities :
#Entity
#Table(name="Registration")
public class Registration{
#Id
private UUID uuid;
#OneToMany(cascade = {CascadeType.PERSIST, CascadeType.REMOVE, CascadeType.MERGE}, fetch = FetchType.LAZY)
#JoinColumn(name="registration", nullable = false)
private List<Payment> payment;
}
#Entity
#Table(name="Payment")
public class Payment {
#Id
private UUID uuid;
/*#ManyToOne(targetEntity = Registration.class) <-- MappingException: Repeated column in mapping for entity
private Registration registration;*/
}
This entities create two tables :
TABLE `registration` (
`uuid` binary(16) NOT NULL,
PRIMARY KEY (`uuid`))
TABLE `payment` (
`uuid` binary(16) NOT NULL,
`registration` binary(16) NOT NULL,
PRIMARY KEY (`uuid`),
CONSTRAINT `FK_jgemihcy9uethvoe3l7mx2bih` FOREIGN KEY (`registration`) REFERENCES `registration` (`uuid`))
I'm using Rest Service. I can access to
registration.payment
but not
payment.registration
why ? I need a relation oneToMany bidirectionnal ?
Yes, you need to add the payment.registration #ManyToOne relationship if you use it in your code.
Take into account that JPA allows you to map a SQL database model to an object oriented one. Once you have the mapping between your objects and your database, you always work at the object level. That's why, although you have the relationship in the database, your Payment object doesn't know anything about it unless you map it to an attribute.
Of course it applies when you are using you data model objects or performing JPQL or Criteria queries. If you use native queries you have access to the database model as it is.
I'm using Spring Boot JPA with Gradle. I'm struggling to find a guide that I can follow which focusses on creating a relational database with the correct Syntax for Spring Boot. I had a go but I get this error
No property idTestCase found for type TestRun!
I want TestRun and TestData entities with a OneToOne relationship with each other, and a TestCase entity that has a OneToMany relationship with TestRun. I reckon that TestRun should contain the foreign keys for TestData and TestCase.
Many times I make changes and it will not build, and when it does build the tables do not look correct, this is what I created:
#Entity
public class TestRun {
#Id #GeneratedValue(strategy = GenerationType.AUTO)
private long testRunId;
private Boolean result;
#OneToOne #JoinColumn(name="testData_id")
private TestData testData;
#ManyToOne #JoinColumn(name="testCase_id")
private TestCase testCase;
}
#Entity
public class TestCase {
#Id #GeneratedValue(strategy = GenerationType.AUTO)
private long testCaseId;
private String name;
private String description;
#OneToMany(cascade=CascadeType.ALL, mappedBy="testCase",targetEntity=TestRun.class)
private Collection<TestRun> testRun;
}
#Entity
public class TestData {
#Id #GeneratedValue(strategy = GenerationType.AUTO)
private long testDataId;
#OneToOne(cascade=CascadeType.ALL, mappedBy="testData",targetEntity=TestRun.class)
private TestRun testRun;
}
From the guides it isn't clear to me what goes in #JoinColumn(name= some say it needs to link to a field on your POJO and some say it doesn't. If I create the foreign key field in my POJO then I get two foreign key fields in the database table and if I don't it doesn't build at all.
For example from the error I can infer it wants me to add the following fields to TestRun:
private long idTestCase;
private long idTestData;
But then my database appears as:
SELECT * FROM TEST_RUN;
TEST_RUN_ID
ID_TEST_CASE
ID_TEST_DATA
RESULT
TEST_CASE_ID
TEST_DATA_ID
(no rows, 3 ms)
I tried setting #JoinColumn(name= to the name of the primary key field on the other side of the relationship but again it did not build.
Many thanks
I found the guide at JBoss to be the most helpful in describing the different mappings.