Nested entity in request body is ignored - spring-mvc

Question

The domain model is
An industry has many companies
A company belongs to an industry
So I have my entity classes:
#Entity
public class Industry {
#Id #GeneratedValue
private Long id;
private String name;
#OneToMany(targetEntity = Company.class, fetch = FetchType.LAZY, mappedBy = "industry")
private Collection<Company> companies = new ArrayList<>(0);
// Getters and setters
}
and
#Entity
public class Company {
#Id #GeneratedValue
private Long id;
private String name;
#ManyToOne(cascade = CascadeType.DETACH, fetch = FetchType.EAGER, optional = false)
private Industry industry;
// Getters and setters
}
My controller:
#RestController
#RequestMapping("/companies")
public class CompaniesController extends ControllerBase {
#RequestMapping(method = RequestMethod.POST)
public Company create(#RequestBody Company company) {
company.getIndustry(); // returns null
// ...
}
}
When I send request POST /companies with request body
{
"name": "Walmart",
"industry": {
"id": 1
}
}
I found that company.getIndustry() always returns null. How can I make the controller accept nested entities?

Answer 1

Entities are session based. They usually work on basis of Lazy loading I.e only the first level is loaded and other attributes are loaded on Demand. You cannot pass it from one layer to other. (service to controller)
The correct way to do it. Have a Value object (a simple class) n the controller. Use it between front end and back end. Send the same value object to service. And use the entity only between Service and DAo layer
public class CompanyVO{
private Long id;
private String name;
private IndustryVO industryVO; // create similar class
// Getters and setters
}
#RestController
#RequestMapping("/companies")
public class CompaniesController extends ControllerBase {
#RequestMapping(method = RequestMethod.POST)
public Company create(#RequestBody CompanyVO companyVO) {
companyVO.getIndustry(); // returns null
// ...
}
}

Answer 2

This may be because you need another Spring message converter instead of the default one. Just add jackson to your pom.xml and Spring will use MappingJackson2HttpMessageConverter.
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.8.5</version>
</dependency>