I have a parent Entity with 2 child entities that are lazily loaded. I would like to load all the associated child entities when the parent entity is loaded
#Entity
public class Author {
#Id
#GeneratedValue
private Long id;
private String firstName;
private String lastName;
#OneToMany(mappedBy ="author",cascade= CascadeType.ALL,fetch=FetchType.LAZY)
private List<Post> posts;
#OneToMany(mappedBy ="author",cascade= CascadeType.ALL,fetch=FetchType.LAZY)
private List<Book> books;
}
Load all Books and Posts based on the Author firstname by using Dynamic query.
public interface AuthorRepository extends CrudRepository<Author, Long> {
public List<Author>findByFirstNameAndPostsAndBooks()
}
The Above Findby does not work, please assist me to construct the correct Query.
Also i am trying to avoid #Query or QueryDSL for the time being
To fetch authors by their firstname you should change you query to this:
public List<Author>findByFirstName(String firstname);
JPA will load the authors posts and books automatically because of your #OneToMany annotations in your Author class.
Add spring.jpa.properties.hibernate.enable_lazy_load_no_trans=true to your application.properties file to enable lazy loading without transactional annotations.
Related
I have a database table in which there is a field which I do not want to map to my model class while making a get call. Is there any annotation to handle this use case?
When persisting Java objects into database records using an Object-Relational Mapping (ORM) framework, we can ignore fields by adding the #Transient annotation to those fields.
#Entity
#Table(name = "Users")
public class User {
#Id
private Integer id;
private String email;
private String password;
#Transient
private Date loginTime;
// getters and setters
}
I have two objects, one parent and one child as follows :
#Entity
#Table(name="category")
public class CategoryModel {
private #Id #GeneratedValue Long id;
private String name;
#OneToMany(mappedBy="category", cascade=CascadeType.PERSIST)
private List<AttributeModel> attributes;
}
#Entity
#Table(name="attribute")
public class AttributeModel {
private #Id #GeneratedValue Long id;
private String name;
#ManyToOne(cascade = CascadeType.ALL)
#JoinColumn(name="category_id")
private CategoryModel category;
}
I also have dtos which maps to these model objects but I ommited them.
When I try to save a category object with this payload Attribute values are also created in the attribute table but with null category ids.
{
"name":"Chemicals",
"attributes":[
{"name": "volume"}, {"name":"humidity"}
]
}
What can I do to have my attribute values persisted into the database with the category id which is created before them?
First of all, this problem is not a "Spring Data JPA" problem, it is a JPA (probably Hibernate) problem.
Analysis
Since you left out the code for the controller and the JSON mapping, I have to guess a bit:
fact 1: The relationship between category and attributes is controlled by the attribute AttributeModel.category but not by CategoryModel.attributes. (That is how JPA works).
observation 2: Your JSON object define CategoryModel.attributes (i.e. opposite to how JPA works).
Without knowing your JSON mapping configuration and controller code, I would guess that the problem is: that your JSON mapper does not set the AttributeModel.category field when it deserialises the JSON object.
Solution
So you need to instruct the JSON mapper to set the AttributeModel.category field during deserialisation. If you use Jackson, you could use:
#JsonManagedReference and
#JsonBackReference
#Entity
#Table(name="category")
public class CategoryModel {
...
#JsonManagedReference
#OneToMany(mappedBy="category", cascade=CascadeType.PERSIST)
private List<AttributeModel> attributes;
}
#Entity
#Table(name="attribute")
public class AttributeModel {
...
#JsonBackReference
#ManyToOne(cascade = CascadeType.ALL)
#JoinColumn(name="category_id")
private CategoryModel category;
}
I solved this by manually setting child object's reference to the parent object as follows :
public Long createCategory(CategoryDto categoryDto) {
CategoryModel categoryModel = categoryDto.toModel(true,true);
categoryModel.getAttributes().forEach(a -> a.setCategory(categoryModel));
return categoryRepository.save(categoryModel).getId();
}
I've a question about One to One unidirectional Mapping in Spring Boot.
I've a Customer class with a One to One unidirectional mapping to an Address class.
But when I try to associate a new customer with an existing Address, the database is updated.
So two Customers are now associated with the one Address.
As I understand it only one Customer should be associated with one unique Address. Do I understand the concept correctly, or am I doing something wrong in Spring Boot/ Spring Data JPA/ Hibernate?
Customer
#Entity
public class Customer {
#Id
private Long cId;
private String cName;
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name="aid")
private Address cAddr;
:
}
Address
#Entity
public class Address {
#Id
private Long aid;
private String town;
private String county;
:
}
data.sql
insert into address values (100, "New York", "NY");
insert into customer values (1, "John Smith", 100);
Application.java
#Override
public void run(String... args) throws Exception {
Customer c1 = new Customer((long)5, "Mr. Men");
Optional<Address> a100 = ar.findById((long)100);
c1.setcAddr(a100.get());
cr.save(c1);
}
Database
There are 2 options on how to make #OneToOne relation: unidirectional and bidirectional: see hibernate doc.
When you scroll down a little bit you will find the following:
When using a bidirectional #OneToOne association, Hibernate enforces the unique constraint upon fetching the child-side. If there are more than one children associated with the same parent, Hibernate will throw a org.hibernate.exception.ConstraintViolationException
It means that you'll have the exception only on fetching and when you have a bidirectional association. Because Hibernate will make an additional query to find the dependent entities, will find 2 of them, which doesn't fit #OneToOne relation and will have to throw an exception.
One way to "fix" uniqueness for your entities, is to make cAddr unique:
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name="aid", unique=true)
private Address cAddr;
If you create your db tables, by setting hbm2ddl property this will add a unique constraint to the aid column.
I really recommend to read the following:
#OneToOne javadoc itself provides examples of how to do everything correctly (for you Examples 1 and 2 are the most useful)
Check Vlad's blog about #OneToOne. It must be the best you can find. At least jump to the chapter "The most efficient mapping" and implement it bidirectional and sharing the PK, using #MapsId.
Also maybe you will come up to the idea to use #ManyToOne option (at least i can imagine that customer can have multiple addresses)
This is not One-to-Many relation. It's One-to-Many as One object has multiple related objects. Checkout this article.
Example:
Post.java
#Getter
#Setter
#AllArgsConstructor
#NoArgsConstructor
#Entity
#Table
public class Post {
#Id
#GeneratedValue
#Column(name = "post_id")
private Long id;
#Column
private String postHeader;
#OneToMany(
cascade = CascadeType.ALL,
orphanRemoval = true
)
private List<Comment> comments = new ArrayList<>();
public void addComment(Comment comment) {
comments.add(comment);
}
public void removeComment(Comment comment) {
comments.remove(comment);
}
// equals() and hashCode()
}
Comment:
#Getter
#Setter
#AllArgsConstructor
#NoArgsConstructor
#Entity
#Table
public class Comment {
#Id
#GeneratedValue
#Column(name = "postcom_id")
private Long id;
#Column
private String text;
// equals() and hashCode()
}
Check out step "3. Uni-directional one-to-one mapping demonstration" at this site basically carbon copy of what you're trying to do.
I am trying to use entity graph for triggering lazy collections to load but unfortunately entity graph also triggers all nested collections. I am using spring-data-jpa-entity-graph library for creating entity graphs at runtime.
#Entity
public class Brand implements Serializable {
#OneToMany(mappedBy = "brand", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private Set<Vehicle> vehicles;
}
#Entity
public class Vehicle implements Serializable {
#ManyToOne
#JoinColumn(name = "brand_id")
private Brand brand;
#OneToMany(mappedBy = "vehicle", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private Set<VehiclePart> parts;
}
#Entity
public class VehiclePart implements Serializable {
#ManyToOne
#JoinColumn(name = "vehicle_id")
private Vehicle vehicle;
}
Spring service with JPA repository:
public interface BrandsRepository extends EntityGraphJpaRepository<Brand, Long> {
Page<Brand> findAll(Pagable pagable, EntityGraph entityGraph);
}
#Service
public class BrandsService {
public List<Brand> find() {
return repository.findAll(PageRequest.of(0, 10, Sort.by(Sort.Direction.ASC, "id")), EntityGraphUtils.fromAttributePaths("vehicles")).getContent();
}
}
In this case service also return parts collection for each vehicle but I would like to fetch only list of brands with vehicles collection for each brand.
How can we trigger to load lazy collections just on the first level (only brand's vehicles -- without vehicle's parts)?
I had the same problem. In my case: Spring and hibernate acted correctly, but I can see, that unused (lazy) fields are queried from sql.
When you use the fields, then they will be loaded over sql.
Iam using lombok and #EqualsAndHashCode.Exclude and #ToString.Exclude helps to prevent that.
In your case: Add a DTO-layer. Do not return the entities themself.
Or use #JsonIgnore annotation to ignore fields.
I have two entity bean :
#Entity
public class User {
#Id
#GeneratedValue
private Long id;
#OneToMany(mappedBy="user", cascade = CascadeType.ALL)
private List<Comment> comments = new ArrayList<Comment>();
//SOME OTHER CLASS VARIABLES
//GETTERS AND SETTERS
}
and my Comment class is like this :
#Entity
public class Comment {
#Id
#GeneratedValue
private Long id;
private String title;
private String content;
#ManyToOne
private User user
//SOME OTHER CLASS VARIABLES
//GETTERS AND SETTERS
}
now I know that I can get the User Object from session and set the user for my comment like this in order to be able to use the join feature in JPA:
commentObject.setUser(TheSessionGrabedUserObject/UserObjectWhichHasFetchedFromDbUsingUserId);
but as long as I have the userId for my user Object I do not need to do this.
I'm looking for a way to insert this foreignKey into my comment table without getting the User Object from session or maybe query to database to fetch it first !
how I'm gonna do it using JPQL ?
You can use the entityManager.getReference() method. In your case:
entityManager.getReference(User.class, userId);
This will not perform any DB query, but will give you a User instance with only the ID populated, and you can pass that to commentObject.setUser().