spring rest lazy loading with hibernate

Question

I am trying to develop spring rest api with hibernate. after searching in google, I have not find solution to lazy loading. I have two entity like below:

University.java

@Entity()
@Table(schema = "core", name = "university")
public class University extends BaseEntity {

    private String uniName;
    private String uniTelephon;


    @LazyCollection(LazyCollectionOption.FALSE)
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "university", cascade = CascadeType.ALL)
    @JsonManagedReference
    private List<Student> students;

//setter and getter
}

Student.java

@Entity
@Table(schema = "core",name = "student")
public class Student {

    @Id
    @GeneratedValue            
    private long id;        

    private String firstName;        

    private String lastName;        

    private String section;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name = "UNIVERSITY_ID",nullable = false)
    @JsonBackReference
    private University university;
    // setter and getter
}

any my rest end point

@GetMapping("/list")
public ResponseEntity list() throws Exception {
    // I need to return just Universities But it return it eagerly with their students
    return new ResponseEntity(this.universityService.findAll(), HttpStatus.OK);
}

after calling the rest api, it return university with all students.

There is a way to tell Jackson to not serialize the unfetched objects or collections?

Can somebody help me with a proved solution?

Although the accepted answer is true, But the better answer is DO NOT return your entities to the client. First convert them to a Data Transfer Object (DTO) and send back those DTO objects to the client. — Ghasem Sadeghi
– Ghasem Sadeghi, Commented Nov 12, 2020 at 19:04

Baptiste Beauvais · Accepted Answer · 2017-09-13 09:34:17Z

5

Try adding the following dependancy (depending on your hibernate version):

<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-hibernate5</artifactId>
    <version>${jackson.version}</version>
</dependency>

And then (assuming you have a Java based configuration) add the following in the WebMvcConfigurerAdapter class:

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    converters.add(jackson2HttpMessageConverter());
}

@Bean
public MappingJackson2HttpMessageConverter jackson2HttpMessageConverter() {
    MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
    converter.setObjectMapper(this.jacksonBuilder().build());

    return converter;
}

public Jackson2ObjectMapperBuilder jacksonBuilder() {
    Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();

    Hibernate5Module hibernateModule = new Hibernate5Module();

    hibernateModule.configure(Feature.FORCE_LAZY_LOADING, false);

    builder.modules(hibernateModule);

    // Spring MVC default Objectmapper configuration
    builder.featuresToDisable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
    builder.featuresToDisable(MapperFeature.DEFAULT_VIEW_INCLUSION);

    return builder;
}

It should force the Jackson's objectMapper to not fetch lazy-loaded values.

edited Sep 13, 2017 at 9:34

answered Sep 13, 2017 at 7:40

Baptiste Beauvais

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4 Comments

Ali Akbarpour Over a year ago

its through the below exception HTTP Status 500 - Could not write content: failed to lazily initialize a collection of role: a2.asena.cashModel.University.students, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->a2.asena.cashModel.University["students"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: a2.asena.cashModel.University.students, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->a2.asena.cashModel.University["students"])

Ali Akbarpour Over a year ago

for above exception solution is overriding Filter in Appinitializer @Override protected Filter[] getServletFilters() { return new Filter[]{new HiddenHttpMethodFilter(), new MultipartFilter(), new OpenEntityManagerInViewFilter()}; is

Ali Akbarpour Over a year ago

some article says it is not proper solution

Baptiste Beauvais Over a year ago

i can't say if it's a proper solution but i don't know others. I changed the answer to make it work with Spring MVC, the way the ObjectMapper was initialize before was wrong my bad.

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