model
Phone numbers is a common entity for both the Student and employee . How to share the phonenumbers as common Child entity to both the Student and Employee.
What you want to do is create a one-to-many relationship between Student and PhoneNumbers and another one-to-many relationship between Employee and PhoneNumbers. In order to do this you can use the annotations #OneToMany and #JoinColumn. Here's how the code for Employee would look:
#Entity
#Table(name="employees")
public class Employee {
...
#OneToMany
#JoinColumn(name="phone_number_id")
private List<PhoneNumber> phoneNumbers;
...
}
This is an example for unidirectional association, there is also a bidirectional one. For more detailed explanation of both associations you can check out this article.
Related
I have two entities Estate and PropertyTags in a Spring Boot application. The Estate entity has a many-to-many relationship with the PropertyTag (PropertyTag is also used by other entities)
This is the Estate entity:
#Entity
public class Estate{
#Id
private Long id;
.
.
#ManyToMany
private Set<PropertyTag> propertyTags;
.
.
// other properties
}
And the PropertyTag class:
#Entity
public class PropertyTag{
#Id
private Long id;
private String tagName;
// getters and setters
}
The above relationship created 3 database tables with one table for foreign keys of the relationship.
I need a repository method (or query) that will retrieve an Estate that will take and argument of an estate Id and property tag object.
I tried using the hibernate keywords as below:
public interface EstateRepository extends JpaRepository<Estate, Long> {
Optional<Estate> findByIdAndPropertyTagsContaining(Long estateId, PropertyTag childTag);
}
But that did not work.
I do not want to retrieve an estate via its ID and manually loop through its property tags to check if a tag exists in its collection. I feel this can be done with a query of the database
I am not so good at writing custom queries. I need help with the query to do that.
Thank you.
To get an Estate entity by the PropertyTag entity you can also just use the id of the PropertyTag and try
Optional<Estate> findByIdAndPropertyTags_Id(Long estateId, Long propertyTagId);
Which should return the Estate containing a tag with the given ID.
Containing is used for String searching
I am doing many to one mapping in hibernate. I am using the existing tables which I created earlier for one to many mapping (customer and order) but when I am trying to map and update those table I couldn't able to I don't know how should I processed? and I would like to insert the data meaning I would like to create some more orders using command line runner for that customer.
Could you please help me with this
Appreciate your help.
Mapping one-to-many and many-to-one association
Both associations are the same association seen from the perspective of the owing and subordinate entities and respectively.
Student one-to-many Address
Address many-to-one Student
#OneToMany annotation can be applied to a field or property value of "one" end entity class for a collection or an array representing the mapped "many" end of the association.
#ManyToONe relationship between two entities is by managing the FK(Foreign key) of the "one" end entity, as a column in the "many" entity table.
> **Bidirectional one-to-many using ```#JoinColumn```**
#Entity
public class Student{
#OneToMany(cascade = CasecadeType.ALL)
#JoinTable(name="Student_FK")
public set<Address> getAddress(){
return address;
}
}
One-to-Many side as the owing side, You have to remove the mappedBy element and set the #ManyToOne #JoinColumn as insertable and updatable to false. This Solution is not optimized and will produce some additional UPDATE Statement.
#Entity
public class Address{
#ManyToOne(cascade = CasecadeType.ALL)
#JoinColumn(name="STUDENT_FK", insertable = false, updatable = false)
public Student student;
}
For more details look at this link Link
For example, if you have an order table in Hibernate and a product table that receives an order, it is mapped as a one to many relationship.Then,Must I write the mapping relationship in code here? In my project, I permanently store order information in a database I have, but in that case, does it need to be a mapping relationship?There's nothing else to do except delete cascade i think.
If you want to use the association in your business code, you also need to model in your domain model. In the described example, I would expect a many-to-many association between the Order and the Product entity. You could model it as a uni- (= only on 1 entity) or bidirectional (= on both entities) association.
Here is a quick example. I provide a very detailed description of all kinds of associations in my guide to association mappings.
public class Order {
#ManyToMany
private Set<Product> products;
...
}
public class Product {
#ManyToMany(mappedBy = "products")
private Set<Order> orders;
...
}
I have an entity Order who declares #ManyToMany relationship.
#ManyToMany is represented by a separate entity with a link to Order.
When I create the instance of Order I can't save #ManyToMany because I'm getting order_id cannot be null.
So I saved Order entity separately from #ManyToMany, created #ManyToMany object, then saved it through own repository, but now I can't attach this #ManyToMany to the Order object.
And when I find Order - it has a null collection of #ManyToMany.
How to update Orders with #ManyToMany?
Your description is unclear, but I'll assume you need to make sure to set your associations right before saving.
Let's assume your other class is called OtherClass. It should have a method called "addOrder", that you need to call before saving it with a repository/dao.
#Entity
public class OtherClass {
#ManyToMany
private List<Order> orders;
public void addOrder(Order order) {
orders.add(order);
order.getOthers().add(this);
}
}
I have an Employee entity class which has a one to many relationship with Skills entity class.
Should we specify cascade in Employee class or in Skills class to achieve the below mentioned conditions
An entry in employee might not have an entry in skills
An entry in employee might have multiple entries in skills
If we delete employee then the corresponding skills of the employee should also be deleted
Map entities like below will fulfill the requirements.
In Employee entity :
#OneToMany(mappedBy="employee",cascade = CascadeType.ALL,fetch=FetchType.LAZY)
private Set<Skill> skills;
In Skill Entity :
#ManyToOne
private Employee employee;
An entry in employee might have multiple entries in skills -- #OneToMany will do this.
If we delete employee then the corresponding skills of the employee should also be deleted --- cascade all will do this.