Hibernate命令外键表

Question

I have a REST API ( Spring REST with Hibernate ), which is the access point for all my data. A client application ( Cordova and AngularJS ) connect to this API for the data feed.

My versions in the REST API are:

Spring: 4.2.3.RELEASE

Hibernate: 4.3.11.Final

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Problem

In the client application I require an ordered list. When I request a list from the REST API, the list is sorted differently almost every time. This is quite annoying, since some text from the list is displayed on the screen and now it seems like it is jumping around.

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Hibernate

In my project I have the following Hibernate setup:

Company

@OneToMany(fetch = FetchType.LAZY, mappedBy = "companyId", cascade = {CascadeType.ALL})
@JsonBackReference
private Set<Employee> employees= new HashSet<Employee>();

Employee

@NotNull
@Column(name = "companyId", nullable = false)
private int companyId;

A company can have many employees, but an employee can only work at one company at a time.

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Hibernate Repository

Due to questions if I am using queries or not, here is my repository (using Criteria / Let hibernate do the job):

public Employee findById(int id) {
   Criteria criteria = getSession().createCriteria(Employee.class);
   criteria.add(Restrictions.eq("id", id));
   return (Employee) criteria.uniqueResult();
}

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Spring

For better data handling I am making use of serialization models. I implemented this one as follows (in my RestController ):

Company company = companyManager.findCompanyWithEmployees(companyName);

Set<Employee> types = company.getEmployees();
Set<EmployeeList> list = new HashSet<EmployeeList>();

for (IncidentType item : types) {
    EmployeeList newItem = new EmployeeList();
    newItem.setId(item.getId())
           .setParent(item.getParent())
           .setChildren(item.getChildren())
           .setTitle(item.getTitle())
           .setImage(item.getImage());

     list.add(newItem);
}

This code creates a List of EmployeeList items, which I return and handle in my AngularJS code.

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I Tried

• I tried adding a Criteria in the Employee repository (findById), but It seems like Hibernate does not use the repository when getting a table via a foreign key.

• Tried adding an annotation, but Hibernate does not have annotation support for order by.

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Extra information

Due to the fact that I use LAZY loading (for performance reasons), I use the following code in my repository:

public Company findCompanyWithInterface(String companyName) {
   Company company = this.findByName(companyName);

   if (company == null) {
       return null;
   }
   //activate hibernate to load the employees (is LAZY loaded)
   Hibernate.initialize(company.getEmployees());

   return company;
}

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My question

Is there any way to tell Hibernate to order the list of Employees it gets via the company entity? I know I can order it in my code, but that is quite bad for the performance. So It would be nice if Hibernate could order the items.

Order by ID should be fine. I can always change that if I want something else.

Anyone knows how I can achieve this without affecting the performance to bad?

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Solution

Hibernate does not have a specific annotation for order by . javax.persistence does have an annotation for ordering ( @OrderBy() ). Hibernate checks this annotation and orders the result.

You need to use an ArrayList for this, so that the order is preserved (answer is below).

Credits to Benjamin Bau for the answer .

Answer 1

Add the @OrderBy annotation to your employees. Change the field from a set to a list so that order is preserved.

@OneToMany(fetch = FetchType.LAZY, mappedBy = "companyId", cascade = {CascadeType.ALL})
@OrderBy("id")
@JsonBackReference
private List<Employee> employees = new ArrayList<Employee>();