How can one configure their JPA Entities to not fetch related entities unless a certain execution parameter is provided.
According to Spring's documentation, 4.3.9. Configuring Fetch- and LoadGraphs, you need to use the #EntityGraph annotation to specify fetch policy for queries, however this doesn't let me decide at runtime whether I want to load those entities.
I'm okay with getting the child entities in a separate query, but in order to do that I would need to configure my repository or entities to not retrieve any children. Unfortunately, I cannot seem to find any strategies on how to do this. FetchPolicy is ignored, and EntityGraph is only helpful when specifying which entities I want to eagerly retrieve.
For example, assume Account is the parent and Contact is the child, and an Account can have many Contacts.
I want to be able to do this:
if(fetchPolicy.contains("contacts")){
account.setContacts(contactRepository.findByAccountId(account.getAccountId());
}
The problem is spring-data eagerly fetches the contacts anyways.
The Account Entity class looks like this:
#Entity
#Table(name = "accounts")
public class Account
{
protected String accountId;
protected Collection<Contact> contacts;
#OneToMany
//#OneToMany(fetch=FetchType.LAZY) --> doesn't work, Spring Repositories ignore this
#JoinColumn(name="account_id", referencedColumnName="account_id")
public Collection<Contact> getContacts()
{
return contacts;
}
//getters & setters
}
The AccountRepository class looks like this:
public interface AccountRepository extends JpaRepository<Account, String>
{
//#EntityGraph ... <-- has type= LOAD or FETCH, but neither can help me prevent retrieval
Account findOne(String id);
}
The lazy fetch should be working properly if no methods of object resulted from the getContacts() is called.
If you prefer more manual work, and really want to have control over this (maybe more contexts depending on the use case). I would suggest you to remove contacts from the account entity, and maps the account in the contacts instead. One way to tell hibernate to ignore that field is to map it using the #Transient annotation.
#Entity
#Table(name = "accounts")
public class Account
{
protected String accountId;
protected Collection<Contact> contacts;
#Transient
public Collection<Contact> getContacts()
{
return contacts;
}
//getters & setters
}
Then in your service class, you could do something like:
public Account getAccountById(int accountId, Set<String> fetchPolicy) {
Account account = accountRepository.findOne(accountId);
if(fetchPolicy.contains("contacts")){
account.setContacts(contactRepository.findByAccountId(account.getAccountId());
}
return account;
}
Hope this is what you are looking for. Btw, the code is untested, so you should probably check again.
You can use #Transactional for that.
For that you need to fetch you account entity Lazily.
#Transactional Annotations should be placed around all operations that are inseparable.
Write method in your service layer which is accepting one flag to fetch contacts eagerly.
#Transactional
public Account getAccount(String id, boolean fetchEagerly){
Account account = accountRepository.findOne(id);
//If you want to fetch contact then send fetchEagerly as true
if(fetchEagerly){
//Here fetching contacts eagerly
Object object = account.getContacts().size();
}
}
#Transactional is a Service that can make multiple call in single transaction
without closing connection with end point.
Hope you find this useful. :)
For more details refer this link
Please find an example which runs with JPA 2.1.
Set the attribute(s) you only want to load (with attributeNodes list) :
Your entity with Entity graph annotations :
#Entity
#NamedEntityGraph(name = "accountGraph", attributeNodes = {
#NamedAttributeNode("accountId")})
#Table(name = "accounts")
public class Account {
protected String accountId;
protected Collection<Contact> contacts;
#OneToMany(fetch=FetchType.LAZY)
#JoinColumn(name="account_id", referencedColumnName="account_id")
public Collection<Contact> getContacts()
{
return contacts;
}
}
Your custom interface :
public interface AccountRepository extends JpaRepository<Account, String> {
#EntityGraph("accountGraph")
Account findOne(String id);
}
Only the "accountId" property will be loaded eagerly. All others properties will be loaded lazily on access.
Spring data does not ignore fetch=FetchType.Lazy.
My problem was that I was using dozer-mapping to covert my entities to graphs. Evidently dozer calls the getters and setters to map two objects, so I needed to add a custom field mapper configuration to ignore PersistentCollections...
GlobalCustomFieldMapper.java:
public class GlobalCustomFieldMapper implements CustomFieldMapper
{
public boolean mapField(Object source, Object destination, Object sourceFieldValue, ClassMap classMap, FieldMap fieldMapping)
{
if (!(sourceFieldValue instanceof PersistentCollection)) {
// Allow dozer to map as normal
return;
}
if (((PersistentCollectiosourceFieldValue).wasInitialized()) {
// Allow dozer to map as normal
return false;
}
// Set destination to null, and tell dozer that the field is mapped
destination = null;
return true;
}
}
If you are trying to send the resultset of your entities to a client, I recommend you use data transfer objects(DTO) instead of the entities. You can directly create a DTO within the HQL/JPQL.
For example
"select new com.test.MyTableDto(my.id, my.name) from MyTable my"
and if you want to pass the child
"select new com.test.MyTableDto(my.id, my.name, my.child) from MyTable my"
That way you have a full control of what is being created and passed to client.
Related
I make a social network and have a post entity that looks like that:
#Entity
public class PostModel {
/* ... */
private String text;
#ManyToMany
private Set<UserModel> likedBy;
}
and a DTO object:
public class PostDto {
/* ... */
private String text;
private Boolean isLikedByMe;
}
To get PostModel's, I use the Specifications API and JpaSpecificationExecutor.
How can I find out the value of the isLikedByMe field for DTO? I can get a UserModel based on username in principal of current Authentication. But what to do next?
I would not like to use Lazy Loading with #PostLoad for this, since with large requests for posts it will seriously slow down the execution.
I also wouldn't want to give up on the Specifications API because of the complexity of some of the queries I create with them.
I'm developing a generic API to fetch data based on the Entity name and its primary key.
URL for get mapping: api/fetch/{id}/data/{entity}
There are many entities present like student, course, instructor, class...
Based on the entity name, the API should return data for that entity by given id in URL.
What should be the best approach using spring boot and JPA?
Trying below, but cannot work when entities are large in number and keep on increasing. Need a generic approach.
#RestController
public class Datacontroller{
#Autowired
CourseRepo courserepo;
#Autowired
Studentrepo studentrepo;
#GetMapping("api/fetch/{id}/data/{entity}")
public <T> T getData(#PathVariable("id") String id, #PathVariable("entity") String entity) {
T l = null;
//depending on entity
if("course".equals(entity)) {
Optional<Course> c = courserepo.findById(id);
l=(T) c.get();
}
if("student".equals(entity)) {
Optional<Student> a = studentrepo.findById(id);
l = (T) a.get();
}
return l;
}
Maybe you should try Spring Data REST. It's a different approach than yours, but it's a Spring project, actively supported and it allows you to directly expose your repositories as REST endpoints.
We can fetch all entities and get entity class from entityName. Once we have class, we can use find method from EntityManager to get the particular record by primary id.
public static Class<?> getEntityClass(EntityManager entityManager, String entityName) {
for (EntityType<?> entity : entityManager.getMetamodel().getEntities()) {
if (entityName.equals(entity.getName())) {
return entity.getJavaType();
}
}
return null;
}
Hello everyone I'm new to Spring world. Actually I want to know how can we use converter to update object instead of updating each element one by one using set and get. Right now in my controller I've :
#PostMapping("/edit/{userId}")
public Customer updateCustomer(#RequestBody Customer newCustomer, #PathVariable final String userId)
{
return customerService.update(userId, newCustomer);
}
and this is how I'm updating the customer object :
#Override
public Customer update(String id, Customer newCustomer) {
Customer customer = customerRepository.findById(id).get();
customer.setFirstName(newCustomer.getFirstName());
customer.setLastName(newCustomer.getLastName());
customer.setEmail(newCustomer.getEmail());
return customerRepository.save(customer);
}
Instead of using each time set and get, I want to use a converter.
The approach of passing the entity's id as a path variable when you're updating it isn't really right. Think about this: you have a #RequestBody, why don't you include the id inside this body too? Why do you want to specify a path variable for it?
Now, if you have the full Customer with its id from the body, you don't have to make any calls to your repository because hibernate adds it to a persistent state already based on its id and a simple
public Customer update(Customer newCustomer) {
return customerRepository.save(newCustomer);
}
should work.
Q: What is a persistent state?
A: A persistent entity has been associated with a database table row and it’s being managed by the current running Persistence Context. ( customerRepository.findById() is just asking the DB if the entity with the specified id exists and add it to a persistent state. Hibernate manage all this process if you have an #Id annotated field and is filled, in other words:
Customer customer = new Customer();
customer.setId(1);
is ALMOST the same thing as :
Customer customer = customerRepository.findById(1).get();
)
TIPS: Anyway, you shouldn't have (if you didn't know) a model in the controller layer. Why? Let's say that your Customer model can have multiple permissions. One possible structure could look like this:
#Entity
public class Customer{
//private fields here;
#OneToMany(mappedBy="customer",--other configs here--)
private List<Permission> permissions;
}
and
#Entity
public class Permission{
#Id
private Long id;
private String name;
private String creationDate;
#ManyToOne(--configs here--)
private Customer customer;
}
You can see that you have a cross reference between Customer and Permission entity which will eventually lead to a stack overflow exception (if you don't understand this, you can think about a recursive function which doesn't have a condition to stop and it's called over and over again => stack overflow. The same thing is happening here).
What can you do? Creating a so called DTO class that you want the client to receive instead of a model. How can you create this DTO? Think about what the user NEEDS to know.
1) Is "creationDate" from Permission a necessary field for the user? Not really.
2) Is "id" from Permission a necessary field for the user? In some cases yes, in others, not.
A possible CustomerDTO could look like this:
public class CustomerDTO
{
private String firstName;
private String lastName;
private List<String> permissions;
}
and you can notice that I'm using a List<String> instead of List<Permission> for customer's permissions which are in fact the permissions' names.
public CustomerDTO convertModelToDto(Customer customer)
{
//hard way
CustomerDTO customerDTO = new CustomerDTO();
customerDTO.setFirstName(customer.getFirstName());
customerDTO.setLastName(customer.getLastName());
customerDTO.setPermissions(
customer.getPermissions()
.stream()
.map(permission -> permission.getName())
.collect(Collectors.toList());
);
// easy-way => using a ModelMapper
customerDTO = modelMapper.map(customer,CustomerDTO.class);
return customerDTO;
}
Use ModelMapper to map one model into another.
First define a function that can map source data into the target model. Use this as a library to use whenever want.
public static <T> void merge(T source, T target) {
ModelMapper modelMapper = new ModelMapper();
modelMapper.getConfiguration().setMatchingStrategy(MatchingStrategies.STRICT);
modelMapper.map(source, target);
}
Use merge for mapping data
Customer customer = customerRepository.findById(id).get();
merge(newCustomer, customer);
customerRepository.save(customer);
Add dependency in pom.xml for model mapper
<dependency>
<groupId>org.modelmapper</groupId>
<artifactId>modelmapper</artifactId>
<version>2.3.4</version>
</dependency>
I have three bean classes: Users ,UserDetail and Auth and i am doing in service class
#Override
public void addUser(UserDetail userDetail) {
Users users=new Users();
users.setUsername(userDetail.getUsername());
users.setEnabled(userDetail.isEnabled());
users.setAgentId(userDetail.getAgentId());
Auth auth = new Auth();
auth.setUsername(userDetail.getUsername());
auth.setAuthority(userDetail.getAuthority());
userDetailDao.addUser(userDetail, users, auth);
}
and i want to save these all object in Dao class like
#Override
public void addUser(UserDetail userDetail,Users users,Auth auth)
{
// TODO Auto-generated method stub
getSession().saveOrUpdate(userDetail);
//Here i also want to save 'users' and 'auth' in same transaction..
getSession().flush();
}
Can it possible to solve you can try it...Thanks.
If you reconstruct your UserDetail class to something like this:
public final class UserDetail
{
private Users user;
private Auth auth;
// Getter and Setter
}
You can just go ahead and store the UserDetail object via Hibernate in the Database.
Of course you need to add the required annotations to the UserDetail class.
Alternativly don't reconstruct UserDetail but create a new class to store both objects in, something like UserDetailDO or UserDetailPersistence or some better name you can totally come up with by yourself.
Just take care with the annotations to set up the relations correctly, like OneToOne or OneToMany.
In your case UserDetail class reference members is used in Users and Auth class, and it can be mapped based on primary key of either UserDetail class or Users class.
So you can re-define those secondary classes(Users and Auth) based on primary key referense of UserDetail class instead of creating objects each time.
Take care of annotations of foreign key references.
Other way of doing this to define base details in a class and extend that class to secondary classes. But most scenarios doesn't work with this approach as the object is created again and again which may have application performance.
The problem is manage your transaction in DAO, the best way is your business layer manage the transaction.
Like this:
class BO {
doSomething() {
DaoA daoA = new DaoA();
DaoB daoB = new DaoB();
transaction.begin();
daoA.insert();
daoB.insert();
transaction.commit();
}
}
See this post too:
Where should "#Transactional" be place Service Layer or DAO
I am using spring boot with spring data jpa and postgre. I have "item" entity that has price, quantity, auto generated int id and order that it belongs to.
I've searched how to edit that entity changing its price and quantity only, without making new entity and the only answer I got is to get the entity from the db and set each property to the new one then save it. But if i have 6 other properties except price and quantity that means in the update method i will set a property 8 times and this seems to me like way too much boilerplate code for spring. My question is: Is there better/default way to do that?
You can provide a copy constructor:
public Item(Item item) {
this(item.price, item.quantity);
}
or use org.springframework.beans.BeanUtils method:
BeanUtils.copyProperties(sourceItem, targetItem, "id");
Then in controller:
#RestController
#RequestMapping("/items")
public class ItemController {
#Autoware
private ItemRepo repo;
#PutMapping("/{id}")
public ResponseEntity<?> update(#PathVariable("id") Item targetItem, #RequestBody Item sourceItem) {
BeanUtils.copyProperties(sourceItem, targetItem, "id");
return ResponseEntity.ok(repo.save(targetItem));
}
}
No, you don't need to set anything for 8 times. If you want to change price and quantity only, just change those two. Put it in a #Transactional method:
#Transactional
public void updateItem(Item item){
// ....
// EntityManager em;
// ....
// Get 'item' into 'managed' state
if(!em.contains(item)){
item = em.merge(item);
}
item.price = newPrice;
item.quantity = newQuantity;
// You don't even need to call save(), JPA provider/Hibernate will do it automatically.
}
This example will generate a SELECT and a UPDATE query. And that's all.
Try using #Query annotation and define your update statement
#Modifying
#Transactional
#Query("update Site site set site.name=:name where site.id=:id")
void updateJustNameById(#Param("id")Long id, #Param("name")String name);
You should use spring data rest which handles all of this by itself. you just have to call a patch request at the specified URL and provide the changed entity properties. if you have some knowledge of spring data rest have a look at https://github.com/ArslanAnjum/angularSpringApi.
Just use this #DynamicUpdate in your Entity class
#DynamicUpdate
public class Item{
}