I have 2 entities and want to perform an inner join on the ID of these two tables. How do I do that? After joining the tables, how do I get the values?
First entity: Employee.java
#Entity
#Table(name = "emp")
public class Employee {
#Id
#Column(name = "id", nullable = false)
private int id;
#Column(name = "language", nullable = false)
private String language;
Second entity: Username.java
#Entity
#Table(name = "users")
public class Username {
#Id
#Column(name = "id", nullable = false)
private int id;
#Column(name = "name", nullable = false)
private String name;
Thanks
I don't know it's helpful for your or not but,
You have to give relationship between those table first(Here i defined bidirectional relationship).
I suppose there is #OneToOne mapping. As like follow,
In Employee Table,
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "username_id")
private Username username;
#OneToOne(mappedBy = "employee")
private Employee employee;
Same way whenever you need those data base on requirement then Place Query as following way in your Employee Repository,
#Query(nativeQuery = true, value="<your-join-query>")
public Employee getEmployeeAllDetails();
For more brief detail follow this kind of tutorials which give you better idea regurding working mechenisum.
https://howtodoinjava.com/
https://www.baeldung.com/
Related
I am struggling with the following problem that I've been trying to solve. After checking solutions on StackOverflow and articles on Baeldung I still get different JPA errors when trying to map the following ONE-TO-ONE relationship between 2 Oracle SQL tables with composite PK in a SpringBoot application:
MASTER
ID
VERSION
1
2022.1
Constraint:
PK_MASTER PRIMARY KEY(ID, VERSION)
MASTER_DETAILS
MASTER_ID
VERSION
DETAILS
1
2022.1
details
Constraint:
PK_MASTER_DETAILS PRIMARY KEY(MASTER_ID, VERSION)
FK_MASTER_DETAILS FOREIGN KEY(MASTER_ID, VERSION) REFERENCES MASTER(ID, VERSION)
After some failures in trying to map it using the #OneToOne JPA annotation with both classes having #EmbeddedId set on the composite PK, I also installed JPA Buddy to check how it will be generated and that resulted in the following 4 classes:
Master.java
#Getter
#Setter
#Entity
#Table(name = "master")
public class Master {
#EmbeddedId
private MasterId id;
#OneToOne(mappedBy = "master")
private MasterDetails masterDetails;
}
MasterId.java
#Getter
#Setter
#Embeddable
public class MasterId implements Serializable {
private static final long serialVersionUID = 8254837075462858051L;
#Column(name = "id", nullable = false)
private BigDecimal id;
#Lob
#Column(name = "version", nullable = false)
private String version;
}
MasterDetails.java
#Getter
#Setter
#Entity
#Table(name = "master_details")
public class MasterDetails {
#EmbeddedId
private MasterDetailsId id;
#MapsId
#OneToOne(fetch = FetchType.LAZY, optional = false)
#JoinColumns({
#JoinColumn(name = "master_id", referencedColumnName = "id", nullable = false),
#JoinColumn(name = "version", referencedColumnName = "version", nullable = false)
})
private Master master;
#Lob
#Column(name = "details", nullable = false)
private String details;
}
MasterDetailsId.java
#Getter
#Setter
#Embeddable
public class MasterDetailsId implements Serializable {
private static final long serialVersionUID = -8375336118866998644L;
#Column(name = "master_id", nullable = false)
private BigDecimal masterId;
#Lob
#Column(name = "version", nullable = false)
private String version;
}
When running the SpringBoot application with this JPA structure the run time error received is:
org.hibernate.PropertyNotFoundException: Could not locate field [id] on class [org.project.packages.MasterDetails]
After removing the #MapsId that cause this error the application starts but when trying to insert data in the tables I get the following error:
org.hibernate.id.IdentifierGenerationException: null id generated for:class org.project.packages.MasterDetails
Checking in the H2 test database I noticed that the FK on the Master_Details table was not present, but only the PK was set.
I would appreciate any help in pointing out how this problem can be solved: other annotations required (Cascade/FetchType) or in case there are any changes to be made to the database level (I also tried adding a separate identifier column in the Master_Details table defined as PK and only keep the FK to the Master table). Thanks in advance!
After many tries, I figured out to solve the issue.
I had to use a common key between the two entities and also FetchType.LAZY.
MasterDetails.class
public class MasterDetails {
#EmbeddedId
#AttributeOverrides({
#AttributeOverride(name="ID", column=#Column(name="MASTER_ID"))
})
private MasterId id;
#OneToOne(fetch = FetchType.LAZY, optional = false)
#JoinColumns({
#JoinColumn(name = "master_id", referencedColumnName = "id", nullable = false),
#JoinColumn(name = "version", referencedColumnName = "version", nullable = false)
})
private Master master;
#Lob
#Column(name = "guidance", nullable = false)
private String guidance;
}
Master.class
public class MasterSheet {
#EmbeddedId
private MasterId id;
#OneToOne(mappedBy = "master", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private MasterDetails masterDetails;
}
I want to join column without object reference. is that possible?
I want to do foreign key without object reference like that
#Data
#Entity
#Table(name = "HRM_EMPLOYEE_SALARY_INCREMENT")
public class EmployeeSalaryIncrement implements Serializable {
private static final long serialVersionUID = 9132875688068247271L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name="ID")
private Integer id;
#Column(name = "REFERENCE_NO")
private String referenceNo;
#ManyToOne
#JoinColumn(name = "AUTHORITY", referencedColumnName = "id")
private Integer authority;
#ManyToOne
#JoinColumn(name = "PART_TWO_REGISTER_ID")
private Integer partTwoRegisterId;
#Column(name = "PART_TWO_ORDER_NO")
private String partTwoOrderNo;
#Column(name = "REMARKS")
private String remarks;
#Column(name = "HRM_TYPE")
private Integer hrmType;
}
If I found solve this problem, it will helpful for me.
Joining is not needed in this case. If you only need the foreign key value, then simply add the column as a #Column like any other:
#Data
#Entity
#Table(name = "HRM_EMPLOYEE_SALARY_INCREMENT")
public class EmployeeSalaryIncrement implements Serializable {
private static final long serialVersionUID = 9132875688068247271L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name="ID")
private Integer id;
#Column(name = "AUTHORITY")
private Integer authority;
// other fields
// ...
}
No, I don't think that you can join columns between two entities without adding the reference of one to the related entity. You will have to create one entity class corresponding to each of your relational database table and add the reference of one to the other to establish relation.
However, I understand that you may not need all the attributes from your related table based upon your use case, and only wish to select one column from it. You can do that either by only adding required attributes in your joined table entity class (if you are sure you won't need other attributes for that table anywhere else).
Or you can use custom queries using JPQL in your repository class which selects only the required attributes from the tables that you have joined.
I will show you an example of the second way:
//Say, this is your entity class where you wish to join other table to fetch only one attribute from the joined table-
#Entity
#Table(name = "TABLE1", schema = "SCHEMA1")
public class Table1 {
#Id
#Column(name = "ID")
private String id;
#Column(name = "TABLE2_COLUMN")
private String table2Column;
#ManyToOne(fetch = FetchType.EAGER)
#JoinColumn(name = "TABLE2_COLUMN1")
private Table2 table2; //refrence of the joined table entity object
}
// And this is the joined table entity class
#Entity
#Table(name = "TABLE2", schema = "SCHEMA1")
public class Table2 {
#Id
#Column(name = "ID")
private String id;
#Column(name = "TABLE2_COLUMN1")
private String table2Column1;
#Column(name = "TABLE2_COLUMN2")
private String table2Column2; // The column which we want to select from the joined table
}
In your repository class -
#Repository
public interface Table1Repository extends JpaRepository<Table1, String> {
#Query("SELECT t1 FROM Table1 t1 WHERE t1.id = :id")
public List<Table1> getTable1Rows(#Param("id") String id);
#Query("SELECT t1.table2.table2Column2 FROM Table1 t1 WHERE t1.id = :id")
public String getTable2Column2(#Param("id") String id);
}
Based upon the response from Markus Pscheidt below, I agree when he said there's no need to join the entities if you only need the attribute which is a foreign key. As foreign key is already present as an attribute in your entity (or table) you are working with.
If you need to fetch any other column apart from foreign key, then you may use JPQL to fetch the exact column that you wish to select.
I have 2 class
public class User {
#Id
#Column(name = "id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String age;
#OneToOne
#JoinColumn(name = "address_id", referencedColumnName = "id")
private Address address;
}
and
public class Address {
#Id
#Column(name = "id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String building;
private String country;
#OneToOne(mappedBy = "address")
private User user;
}
in my table address, I have a few rows.
When I insert table user with data
{
"id":null,
"name":"Foo",
"age":"18",
"address":{
"id":1,
"building":"Too",
"country":"ABS"
}
}
Table user have 1 row with address_id =1.
I insert same data as above
Table user have 2 row with address_id =1.
My answer is: why 2 table connected by one to one can happen the above case?
You can find your answer here
Why #OneToOne is allowing duplicate associations?
Basically, #JoinColumn(name = "address_id", referencedColumnName = "id") alone doesn't serve the semantics of one-to-one in the database, you need to add unique=true into the #JoinColumn, which makes it #JoinColumn(name = "address_id", referencedColumnName = "id", unique = true).
Side-note: I suggest you drop your tables and then re-creating them before trying this out. If you are using Hibernate, you can set hibernate.hbm2ddl.auto to create-drop
I have a table Student which is one to many with Address table and Address have many to one relation to Student table.
public class Student{
#Id
#Column(name = "stud_id", nullable = false)
private String stud_id;
#Column(name = "stud_name", nullable = false)
private String stud_name;
#OneToMany(mappedBy = "student")
private List<Address> addresses;
}
public class Address{
#Id
#Column(name = "address_id", nullable = false)
private String address_id;
#Column(name = "address_name", nullable = false)
private String address_name;
#ManyToOne
#JoinColumn(name = "stud_id", nullable = false)
private Student student;
}
How do i filter something like get All Student addresses address_name in 'Something'.
Expected return should be Student object so that i can traverse into Address which is filtered as 'Something' using Spring JPA repository with SpringConvention or by #Query. Please help
try this if you have a collection of addressNames to filter against
#Query("select a.student from Address a where a.address_name in (?1)")
List<Student> findStudentsByAddressNameIn(List<String> addressNames);
or if you want to filter by address_name = 'something'
#Query("select a.student from Address a where a.address_name = ?1")
List<Student> findStudentsByAddressName(String addressNameFilter);
or if you want to filter by address_name contains 'something' set addressNameFilter to "%" + addressNameFilter + "%" and use
#Query("select a.student from Address a where a.address_name like ?1")
List<Student> findStudentsByAddressNameLike(String addressNameFilter);
I have two entities. One of them is a child of the other one with a relation with OneToMany. Is it possible to implement search criteria that looks up simultaneously in both the main entity and all the child entities?
Example: I have a Company with many employees. If I search with some text, I want to retrieve all the companies, which title contains that text or its employee's names contain that text.
Here are the example entities:
#Entity
public class Company extends AbstractEntity {
#Column(nullable = false, unique = true)
private String uuid;
#Column(nullable = false)
private String companyName;
#OneToMany(mappedBy = “company”, cascade = CascadeType.ALL, fetch = FetchType.EAGER, orphanRemoval = true)
protected Set<Employee> employees = new HashSet<>();
}
#Entity
public class Employee extends AbstractEntity {
#Column(nullable = false, unique = true)
private String uuid;
#Column(nullable = false)
private String firstName;
#Column(nullable = false)
private String lastName;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = “company_id”, nullable = false)
#OnDelete(action = OnDeleteAction.CASCADE)
private Company company;
}
Here is the example query, that I want to transform into Specification criteria
#Query(value = “SELECT DISTINCT c from Company c left outer join c.employees e
WHERE c.companyName LIKE CONCAT('%',:text,'%')
or e.firstName LIKE CONCAT('%',:text,'%')
or e.lastName LIKE CONCAT('%',:text,'%')”)
If you are using Spring JPA data repository, your interface method would look like this.
Company findByCompanyNameConatainingOrEmployeesFirstNameConatainingOrEmployeeslastNameConataining(String searchTextCompanyTitle, String searchTextEmployeeFName, String searchTextEmployeeLName);
If you are not using data repository, please explain your data access design to get an accurate answer.