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Java, list sorting with reflection

I want to allow to sort by every field in the class, without having to write switch/ if statements.
My idea was to find the Field that matches given string value by name and then, with Stream API neatly sort. IntelliJ screamed that i need to surround it with try-catch, so it is not so neatly looking, but that's not important, as it does not work.
private List<MyEntity> getSorted(List<MyEntity> list, SearchCriteria criteria) {
Field sortByField = findFieldInListByName(getFieldList(MyEntity.class), criteria.getSortBy());
return list.stream().sorted(Comparator.comparing(entity-> {
try {
return (MyEntity) sortByField.get(entity);
} catch (IllegalAccessException e) {
e.printStackTrace();
}
return entity;
})).collect(Collectors.toList());
}
In the MyEntity class I have added Comparable interface, but I am not sure what should be in the body of Compare(), as I dont want to specify how to compare objects, because it will change based on the selected sorting.
EDIT: Added Entity below:
#Data
#Entity
#Table(name = "role_management", schema = "mdr")
#Builder
#NoArgsConstructor
#AllArgsConstructor
#EqualsAndHashCode
public class MyEntity implements Comparable{
#Id
#Column(name = "uuid", unique = true, insertable = false, updatable = false)
#GeneratedValue(strategy = GenerationType.AUTO)
private UUID uuid;
#ManyToOne
#JoinColumn(name = "user_id", nullable = false)
private UserEntity user;
#Basic
#NonNull
#Column(name = "role")
private String role;
#Basic
#Column(name = "action")
#Enumerated(EnumType.STRING)
private RoleAction action;
#Basic
#Column(name = "goal")
#Enumerated(EnumType.STRING)
private RoleGoal goal;
#Column(name = "date")
private LocalDateTime date;
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "reporter_id", referencedColumnName = "uuid")
private UserEntity reporter;
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "authorizer_id", referencedColumnName = "uuid")
private UserEntity authorizer;
#Basic
#Column(name = "ezd")
private String ezd;
#Basic
#Column(name = "is_last")
private boolean isMostRecent;
#Override
public int compareTo(Object o) {
return 0;
}
}
EDIT 2: My code based on the #Sweeper solution:
UserEntity (nullable)
#Override
public int compareTo(UserEntity other) {
if (other == null) {
return 1;
}
return this.getMail().compareTo(other.getMail());
}
Comparator:
public static Comparator getSortComparator(Field sortByField) {
return Comparator.nullsLast(Comparator.comparing(entity -> {
try {
Object fieldValue = sortByField.get(entity);
if (!(fieldValue instanceof Comparable<?>) && fieldValue != null) {
throw new IllegalArgumentException("...");
}
return (Comparable) fieldValue;
} catch (IllegalAccessException e) {
throw new MdrCommonException(e.getLocalizedMessage());
}
}));
}

MyEntity should not implement Comparable. It is the fields, by which you are going to sort the list of MyEntity objects, that needs to be Comparable. For example, if you are sorting by the field user, which is a UserEntity, then UserEntity is the thing that needs to be comparable, not MyEntity.
The lambda's job should just be to check that the fields are indeed Comparable, and throw an exception if they are not.
Since you don't know the types of the fields at compile time, however, you'd have to use a raw type here. The comparing call would look like this:
Comparator.comparing(entity -> {
try {
Object fieldValue = sortByField.get(entity);
// This check still passes if the type of fieldValue implements Comparable<U>,
// where U is an unrelated type from the type of fieldValue, but this is the
// best we can do here, since we don't know the type of field at compile time
if (!(fieldValue instanceof Comparable<?>) && fieldValue != null) {
throw new IllegalArgumentException("Field is not comparable!");
}
return (Comparable)fieldValue;
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
})

You can create automatically comparators for any field of any class using reflection but is better create specific comparators (will be typechecked).
Your entity is a normal class with normal fields then, the usual Java sorting machinery should do the job:
Basically, if you define one comparator for every field (even deep fields into your entity):
public final static Comparator<MyEntity> ByField1 = comparing(MyEntity::getField1);
public final static Comparator<MyEntity> ByField2 = comparing(MyEntity::getField2);
public final static Comparator<MyEntity> ByField3 = comparing(MyEntity::getField3);
public final static Comparator<MyEntity> ByDeep1 = comparing(a -> a.getField4().getDeep1());
public final static Comparator<MyEntity> ByDeep2 = comparing(a -> a.getField4().getDeep2());
public final static Comparator<MyEntity> ByDeep3 = comparing(a -> a.getField4().getDeep3());
You can sort using complex sorting expressions:
data.stream()
.sorted(ByField2.reversed().thenComparing(ByDeep2))
.forEach(System.out::println);
a full example could be
public static void main(String[] args) {
List<MyEntity> data =
Stream.of("Row1", "Row2").flatMap(field1 ->
Stream.of(101, 102).flatMap(field2 ->
Stream.of(true, false).flatMap(field3 ->
Stream.of("Row1", "Row2").flatMap(deep1 ->
Stream.of(101, 102).flatMap(deep2 ->
Stream.of(true, false).map(deep3 ->
new MyEntity(field1, field2, field3, new MyDeepField(deep1, deep2, deep3))))))))
.collect(toList());
data.stream()
.sorted(ByField2.reversed().thenComparing(ByDeep2))
.forEach(System.out::println);
}
#Getter
#Setter
#AllArgsConstructor
static class MyDeepField {
private String deep1;
private Integer deep2;
private Boolean deep3;
}
#Getter
#Setter
#AllArgsConstructor
static class MyEntity {
private String field1;
private Integer field2;
private Boolean field3;
private MyDeepField field4;
public final static Comparator<MyEntity> ByField1 = comparing(MyEntity::getField1);
public final static Comparator<MyEntity> ByField2 = comparing(MyEntity::getField2);
public final static Comparator<MyEntity> ByField3 = comparing(MyEntity::getField3);
public final static Comparator<MyEntity> ByDeep1 = comparing(a -> a.getField4().getDeep1());
public final static Comparator<MyEntity> ByDeep2 = comparing(a -> a.getField4().getDeep2());
public final static Comparator<MyEntity> ByDeep3 = comparing(a -> a.getField4().getDeep3());
#Override
public String toString() {
return "MyEntity{" +
"field1='" + field1 + '\'' +
", field2=" + field2 +
", field3=" + field3 +
", deep1=" + field4.getDeep1() +
", deep2=" + field4.getDeep2() +
", deep3=" + field4.getDeep3() +
'}';
}
}
with output
MyEntity{field1='Row1', field2=102, field3=true, deep1=Row1, deep2=101, deep3=true}
MyEntity{field1='Row1', field2=102, field3=true, deep1=Row1, deep2=101, deep3=false}
...
MyEntity{field1='Row2', field2=101, field3=false, deep1=Row2, deep2=102, deep3=true}
MyEntity{field1='Row2', field2=101, field3=false, deep1=Row2, deep2=102, deep3=false}
The criteria field into your SearchCriteria class is some field of type Comparator<MyEntity> or a mapping using an enumeration or parsing string expressions or so...

MongoDB repository save() do the insert instead of update

I am writing a PUT request API with spring and mongodb. But the save() inserts a new object instead of update the current one.
#Document("Test")
public class Expense {
#Field(name = "name")
private String expenseName;
#Field(name = "category")
private ExpenseCategory expenseCategory;
#Field(name = "amount")
private BigDecimal expenseAmount;
public Expense( String expenseName, ExpenseCategory expenseCategory, BigDecimal expenseAmount) {
this.expenseName = expenseName;
this.expenseCategory = expenseCategory;
this.expenseAmount = expenseAmount;
}
public String getExpenseName() {
return expenseName;
}
public void setExpenseName(String expenseName) {
this.expenseName = expenseName;
}
public ExpenseCategory getExpenseCategory() {
return expenseCategory;
}
public void setExpenseCategory(ExpenseCategory expenseCategory) {
this.expenseCategory = expenseCategory;
}
public BigDecimal getExpenseAmount() {
return expenseAmount;
}
public void setExpenseAmount(BigDecimal expenseAmount) {
this.expenseAmount = expenseAmount;
}
}
This is my reporsitory class
public interface ExpenseRepository extends MongoRepository<Expense, String> {
}
This is my Service class which shows how to update the class.
#Service
public class ExpenseService {
private final ExpenseRepository expenseRepository;
public ExpenseService(ExpenseRepository expenseRepository) {
this.expenseRepository = expenseRepository;
}
public void updateExpense(String id, Expense expense){
Expense savedExpense = expenseRepository.findById(id)
.orElseThrow(() -> new RuntimeException(
String.format("Cannot Find Expense by ID %s", id)));
savedExpense.setExpenseName(expense.getExpenseName());
savedExpense.setExpenseAmount(expense.getExpenseAmount());
savedExpense.setExpenseCategory(expense.getExpenseCategory());
expenseRepository.save(savedExpense);
}
}
This is my controller
#RestController
#RequestMapping("/api/expense")
public class ExpenseController {
private final ExpenseService expenseService;
public ExpenseController(ExpenseService expenseService) {
this.expenseService = expenseService;
}
#PutMapping("/{id}")
public ResponseEntity<Object> updateExpense(#PathVariable String id, #RequestBody Expense expense){
expenseService.updateExpense(id, expense);
return ResponseEntity.ok().build();
}
}
As shown in mongodb compass, mongodb auto generates an _id field for every object. So I do not define a id field or use #id annotation to define a primary for the collection. However, in the service class, expenseRepository.findById(id) retrieves the desired object and update it. Why does save() do the insert instead of update? Many thanks.

JPA Can't find the existing entry as no id field id set. You need to add an id field and set generation type to auto.
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int id;

Trigger #OneToMany lazy fetch

I have an ExampleRequest entity that can optionally have one or more ExampleRequestYear. It's currently configured this way (unrelated fields and gettters/setters omitted for brevity, please let me know if you need anything else):
#Entity
#Table(name = "EXAMPLE_REQUEST")
#SequenceGenerator(name = "EXAMPLE_REQUEST_ID_SEQ", sequenceName = "EXAMPLE_REQUEST_ID_SEQ", allocationSize = 1)
#Cacheable(false)
public class ExampleRequest implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "EXAMPLE_REQUEST_ID_SEQ")
#Column(name="EXAMPLE_REQUEST_ID", nullable = false)
private Long exampleRequestId;
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "exampleRequest")
private List<ExampleRequestYear> exampleRequestYearList;
public ExampleRequest() {
}
public List<ExampleRequestYear> getExampleRequestYearList() {
if(this.exampleRequestYearList == null){
this.exampleRequestYearList = new ArrayList<ExampleRequestYear>();
}
return this.exampleRequestYearList;
}
public void setExampleRequestYearList(List<ExampleRequestYear> exampleRequestYearList) {
this.exampleRequestYearList = exampleRequestYearList;
}
public ExampleRequestYear addExampleRequestYear(ExampleRequestYear exampleRequestYear) {
getExampleRequestYearList().add(exampleRequestYear);
exampleRequestYear.setExampleRequest(this);
return exampleRequestYear;
}
public ExampleRequestYear removeExampleRequestYear(ExampleRequestYear exampleRequestYear) {
getExampleRequestYearList().remove(exampleRequestYear);
exampleRequestYear.setExampleRequest(null);
return exampleRequestYear;
}
}
#Entity
#Table(name = "EXAMPLE_REQUEST_YEAR")
#IdClass(ExampleRequestYearPK.class)
public class ExampleRequestYear implements Serializable {
#Id
#Column(nullable = false)
private Integer year;
#Id
#ManyToOne
#JoinColumn(name = "EXAMPLE_REQUEST_ID", referencedColumnName = "EXAMPLE_REQUEST_ID")
private ExampleRequest exampleRequest;
public ExampleRequestYear() {
}
public void setExampleRequest(ExampleRequest exampleRequest) {
this.exampleRequest = exampleRequest;
}
public ExampleRequest getExampleRequest() {
return exampleRequest;
}
}
Part of the code was auto-generated by the IDE and I'm still wrapping my head around JPA so there're probably design mistakes all around.
My app works (apparently) when I create a new ExampleRequest:
ExampleRequest exampleRequest = new ExampleRequest();
ExampleRequestYear exampleRequestYear = new ExampleRequestYear(2020);
request.addExampleRequestYear(exampleRequestYear);
However, I can't figure out how to edit an existing ExampleRequest because I'm unsure on how I'm meant to retrieve the linked entities. According to articles I've read, lazy fetching should be automatic, yet when I try this:
ExampleRequest exampleRequest = employeeRequestsController.getExampleRequestById(123);
System.out.println(exampleRequest.getExampleRequestYearList().size());
... I get a null pointer exception upon .size() because the getter runs but neither initialises an empty list, nor retrieves items from DB:
public List<ExampleRequestYear> getExampleRequestYearList() {
if(this.exampleRequestYearList == null){
// Field is null and conditional is entered
this.exampleRequestYearList = new ArrayList<ExampleRequestYear>();
// After initialisation, field is still null!
}
return this.exampleRequestYearList;
}
Also, switch to FetchType.EAGER solves this particular problem entirely. What am I missing?
Further details regarding app design. The Resource classes that handle HTTP requests interact with a set of Controller classes like this:
#Stateless(name = "ISomeActionController", mappedName = "ISomeActionController")
public class SomeActionController implements ISomeActionController {
#EJB
private IFooDAO fooDao;
#EJB
private IBarDAO barDao;
#Override
public ExampleRequest getExampleRequestById(Long exampleRequestId) {
return fooDao.getEntityById(exampleRequestId);
}
}
It's in the DAO classes where EntityManager is injected an used:
#Local
public interface IGenericDAO<T> {
public T persistEntity(T o);
public T persistEntityCommit(T o);
public void removeEntity(T o);
public void removeEntity(long id);
public T mergeEntity(T o);
public List<T> getEntitiesFindAll();
public List<T> getEntitiesFindAllActive();
public T getEntityById(Object id);
}
public interface IFooDAO extends IGenericDAO<ExampleRequest> {
public void flushDAO();
public ExampleRequest getExampleRequestById(Long exampleRequestId);
}
#Stateless(name = "IFooDAO", mappedName = "IFooDAO")
public class FooDAO extends GenericDAO<ExampleRequest> implements IFooDAO {
public FooDAO() {
super(ExampleRequest.class);
}
#Override
public void flushDAO(){
em.flush();
}
#Override
public ExampleRequest getExampleRequestById(Long exampleRequestId){
String sql = "...";
Query query = em.createNativeQuery(sql, ExampleRequest.class);
//...
}
}

Simple xml returns null value for attribute field

I want to use Simple XML to deserialize the following XML into a POJO:
<shippingInfo>
<shippingServiceCost currencyId="USD">9.8</shippingServiceCost>
<shippingType>Flat</shippingType>
<shipToLocations>Worldwide</shipToLocations>
<expeditedShipping>true</expeditedShipping>
<oneDayShippingAvailable>false</oneDayShippingAvailable>
<handlingTime>3</handlingTime>
</shippingInfo>
I have created the following class to do so. However, I'm having trouble in that the currencyId attribute isn't being properly deserialized.
#Root(name = "shippingInfo")
public class ShippingInfo {
#Element(name = "shippingServiceCost", required = false)
private BigDecimal shippingServiceCost;
#Attribute(name = "currencyId", required = false)
private String currencyId;
#Element(name = "shippingType", required = false)
private String shippingType;
#Element(name = "shipToLocations" ,required = false)
private String shipToLocations;
#Element(name = "expeditedShipping", required = false)
private Boolean expeditedShipping;
#Element(name = "oneDayShippingAvailable", required = false)
private Boolean oneDayShippingAvailable;
#Element(name = "handlingTime", required = false)
private Integer handlingTime;
// Getters & Setters
public BigDecimal getShippingServiceCost() {
return shippingServiceCost;
}
public void setShippingServiceCost(BigDecimal shippingServiceCost) {
this.shippingServiceCost = shippingServiceCost;
}
public String getCurrencyId() {
return currencyId;
}
public void setCurrencyId(String currencyId) {
this.currencyId = currencyId;
}
public String getShippingType() {
return shippingType;
}
public void setShippingType(String shippingType) {
this.shippingType = shippingType;
}
public String getShipToLocations() {
return shipToLocations;
}
public void setShipToLocations(String shipToLocations) {
this.shipToLocations = shipToLocations;
}
public Boolean isExpeditedShipping() {
return expeditedShipping;
}
public void setExpeditedShipping(Boolean bool) {
this.expeditedShipping = bool;
}
public Boolean isOneDayShippingAvailable() {
return oneDayShippingAvailable;
}
public void setOneDayShippingAvailable(Boolean bool) {
this.oneDayShippingAvailable = bool;
}
public Integer getHandlingTime() {
return handlingTime;
}
public void setHandlingTime(Integer days) {
this.handlingTime = days;
}
}
I would expect the value of currencyId to be "USD" after deserializing, but I'm getting null. All the element values appear to deserialize properly. Does anyone have a suggestion on how to fix this?
Moreover, in a case such as the following instance:
<sellingStatus>
<currentPrice currencyId="USD">125.0</currentPrice>
<convertedCurrentPrice currencyId="USD">125.0</convertedCurrentPrice>
<bidCount>2</bidCount>
<sellingState>EndedWithSales</sellingState>
</sellingStatus>
Where there are two attributes named currencyId on two distinct elements, how can I go about deserializing these into separate fields? I have created a similar SellingStatus class but am unsure how to distinguish between the currencyId attributes.
Thank you!
Edit: Per suggestions I tried adding a custom ShippingServiceCost class to ShippingInfo as follows:
#Element(name = "shippingServiceCost", required = false)
private ShippingServiceCost shippingServiceCost;
Which in turn looks like this:
public class ShippingServiceCost {
#Element(name = "shippingServiceCost", required = false)
private BigDecimal shippingServiceCost;
#Attribute(name = "currencyId", required = false)
private String currencyId;
// getters and setters
}
But when I try to access both the shippingServiceCost field and the currencyId field, I get null in every instance (even though I know there is data). Any suggestions are greatly appreciated.

For the above code, SimpleXML expects the currencyId to be present as <shippingInfo currencyId="USD">.
So to solve it, you need to create another class called ShippingServiceCost which will contain the currencyId attribute and the BigDecimal
This will also solve your second query. You can do it by creating two classes CurrentPrice and ConvertedCurrentPrice which will contain the currencyId attribute.

The only working solution is creating a Converter class, see code below:
public class ShippingInfoConverter implements Converter<ShippingInfo> {
#Override
public ShippingInfo read(InputNode inputNode) throws Exception {
ShippingInfo shippingInfo = new ShippingInfo();
InputNode shippingServiceCostNode = inputNode.getNext("shippingServiceCost");
shippingInfo.setShippingServiceCost(new BigDecimal(shippingServiceCostNode.getValue()));
shippingInfo.setCurrencyId(shippingServiceCostNode.getAttribute("currencyId").getValue());
shippingInfo.setShippingType(inputNode.getNext("shippingType").getValue());
shippingInfo.setShipToLocations(inputNode.getNext("shipToLocations").getValue());
shippingInfo.setExpeditedShipping(Boolean.parseBoolean(inputNode.getNext("expeditedShipping").getValue()));
shippingInfo.setOneDayShippingAvailable(Boolean.parseBoolean(inputNode.getNext("oneDayShippingAvailable").getValue()));
shippingInfo.setHandlingTime(Integer.valueOf(inputNode.getNext("handlingTime").getValue()));
return shippingInfo;
}
#Override
public void write(OutputNode outputNode, ShippingInfo shippingInfo) throws Exception {
OutputNode shippingServiceCostNode = outputNode.getChild("shippingServiceCost");
shippingServiceCostNode.setValue(shippingInfo.getShippingServiceCost().toString());
shippingServiceCostNode.setAttribute("currencyId", shippingInfo.getCurrencyId());
outputNode.getChild("shippingType").setValue(shippingInfo.getShippingType());
outputNode.getChild("shipToLocations").setValue(shippingInfo.getShipToLocations());
outputNode.getChild("expeditedShipping").setValue(Boolean.toString(shippingInfo.isExpeditedShipping()));
outputNode.getChild("oneDayShippingAvailable").setValue(Boolean.toString(shippingInfo.isOneDayShippingAvailable()));
outputNode.getChild("handlingTime").setValue(Integer.toString(shippingInfo.getHandlingTime()));
}
}
Note how 'currencyId' is set, using the node's getAttribute method.
shippingInfo.setCurrencyId(shippingServiceCostNode.getAttribute("currencyId").getValue());
Also note how the element 'shippingServiceCost' gets the attribute
shippingServiceCostNode.setAttribute("currencyId", shippingInfo.getCurrencyId());
A few other things are need to get this working, starting with your POJO
#Root(name = "shippingInfo")
#Convert(ShippingInfoConverter.class)
public class ShippingInfo {
#Element(name = "shippingServiceCost", required = false)
private BigDecimal shippingServiceCost;
private String currencyId;
#Element(name = "shippingType", required = false)
private String shippingType;
#Element(name = "shipToLocations" ,required = false)
private String shipToLocations;
#Element(name = "expeditedShipping", required = false)
private Boolean expeditedShipping;
#Element(name = "oneDayShippingAvailable", required = false)
private Boolean oneDayShippingAvailable;
#Element(name = "handlingTime", required = false)
private Integer handlingTime;
// Getters & Setters
public BigDecimal getShippingServiceCost() {
return shippingServiceCost;
}
public void setShippingServiceCost(BigDecimal shippingServiceCost) {
this.shippingServiceCost = shippingServiceCost;
}
public String getCurrencyId() {
return currencyId;
}
public void setCurrencyId(String currencyId) {
this.currencyId = currencyId;
}
public String getShippingType() {
return shippingType;
}
public void setShippingType(String shippingType) {
this.shippingType = shippingType;
}
public String getShipToLocations() {
return shipToLocations;
}
public void setShipToLocations(String shipToLocations) {
this.shipToLocations = shipToLocations;
}
public Boolean isExpeditedShipping() {
return expeditedShipping;
}
public void setExpeditedShipping(Boolean bool) {
this.expeditedShipping = bool;
}
public Boolean isOneDayShippingAvailable() {
return oneDayShippingAvailable;
}
public void setOneDayShippingAvailable(Boolean bool) {
this.oneDayShippingAvailable = bool;
}
public Integer getHandlingTime() {
return handlingTime;
}
public void setHandlingTime(Integer days) {
this.handlingTime = days;
}
}
Adding the line below points SimpleXML to the converter class
#Convert(ShippingInfoConverter.class)
The other change is removing the #Attribute annotation.
One last thing required is that your driver class needs to have AnnotationStrategy enabled
when serialising and deserialing your objects.
Serializer serializer = new Persister(new AnnotationStrategy());

How to get Hibernate JPA to manage list index automagically?

How do I setup a basic OneToMany relationship using a List and get Hibernate JPA to manage the sequence index number of the list automagically? Can this be done?
This is my test case (more or less);
#Table(name="Policy_Root")
public class PolicyRoot extends BaseDomainModel {
private List<Policy> policyList = new ArrayList<Policy>();
#OneToMany(targetEntity=Policy.class, mappedBy="policyRoot", cascade=CascadeType.ALL)
#IndexColumn(name="policy_sequence", base=0, nullable=false)
public List<Policy> getPolicyList() {
return policyList;
}
public void setPolicyList(List<Policy> policyList) {
this.policyList = policyList;
}
public void addPolicy(Policy policy) {
policyList.add(policy);
policy.setPolicyRoot(this);
}
public void addPolicy(int sequence, Policy policy) {
policyList.add(sequence, policy);
policy.setPolicyRoot(this);
}
}
#Entity()
#Table(name="Policy")
public class Policy extends BaseDomainModel {
/** The position of this policy record within the list of policy's belong to the parent PolicyRoot */
private int policySequence;
/** Birectional pointer to parent */
private PolicyRoot policyRoot;
#Column(name="policy_sequence")
public int getPolicySequence() {
return policySequence;
}
public void setPolicySequence(int policySequence) {
this.policySequence = policySequence;
}
#ManyToOne
#JoinColumn(name="policy_root_oid", nullable=false)
public PolicyRoot getPolicyRoot() {
return policyRoot;
}
public void setPolicyRoot(PolicyRoot policyRoot) {
this.policyRoot = policyRoot;
}
}
#Test
public void testCreation() {
Policy policy1 = new Policy();
Policy policy2 = new Policy();
// Uncomment the following and the test case works - but I don't want to manage the sequence numbers
//policy2.setPolicySequence(1);
PolicyRoot policyRoot = new PolicyRoot();
policyRoot.addPolicy(policy1);
policyRoot.addPolicy(policy2);
ServiceImplFacade.getPersistenceFacade().persistSingleItem(policyRoot);
Long oid = policyRoot.getOid();
PolicyRoot policyRootFromDB = ServiceImplFacade.getPersistenceFacade().getEntityManager().find(PolicyRoot.class, oid);
assertEquals(2, policyRootFromDB.getPolicyList().size());
}
If I uncomment the policy2.setPolicySequence(1); line then the test case passes, but I don't think I need to do this. I want Hibernate to do this for me. My understanding is that it can, but if it can't then knowing that it can't would be a good answer as well.
I've tried various combinations of setting nullable, insertable and updateable but I may have missed one.
Is this possible? - If so how?

Found the answer, - it was around getting the right combinations of nullable and insertable. Also had to make the "child index" at Integer so that it could be nullable, and there's also an "optional" flag in the following as well.
public class PolicyRoot extends BordereauxBaseDomainModel {
private List<Policy> policyList = new ArrayList<Policy>();
#OneToMany(cascade=CascadeType.ALL)
#IndexColumn(name="policy_sequence", nullable=false, base=0)
#JoinColumn(name="policy_root_oid", nullable=false)
public List<Policy> getPolicyList() {
return policyList;
}
public void setPolicyList(List<Policy> policyList) {
this.policyList = policyList;
}
}
public class Policy extends BordereauxBaseDomainModel {
/** The position of this policy record within the list of policy's belong to the parent PolicyRoot */
private Integer policySequence;
/** Birectional pointer to parent */
private PolicyRoot policyRoot;
#Column(name="policy_sequence", insertable=false, updatable=false)
public Integer getPolicySequence() {
return policySequence;
}
public void setPolicySequence(Integer policySequence) {
this.policySequence = policySequence;
}
#ManyToOne(optional=false)
#JoinColumn(name="policy_root_oid", insertable=false, updatable=false, nullable=false)
public PolicyRoot getPolicyRoot() {
return policyRoot;
}
public void setPolicyRoot(PolicyRoot policyRoot) {
this.policyRoot = policyRoot;
}
}
Found the answers on the following page after searching Google for a while.
http://opensource.atlassian.com/projects/hibernate/browse/HHH-4390

Do something like this:
#Entity
class Parent {
#OneToMany
#IndexColumn(name = "index_column")
List<Child> children;
}
#Entity
class Child {
#ManyToOne
Parent parent;
#Column(name = "index_column")
Integer index;
#PrePersist
#PreUpdate
private void prepareIndex() {
if (parent != null) {
index = parent.children.indexOf(this);
}
}
}

I'm going to post this answer since I recently had the same issue and this question, although outdated, keeps coming up in the researches.
The #IndexColumn annotation has been deprecated a long time ago and in its place it is best recommended using the #OrderColumn annotation. The second annotation not only simplifies its syntax without having to specify the base attribute, but it also avoids declaring an extra field in the detail class, in this case the policySequence field within the Policy class.
Here is the updated version of the previous snippet:
#Table(name="Policy_Root")
public class PolicyRoot extends BaseDomainModel {
private List<Policy> policyList = new ArrayList<Policy>();
#OneToMany(targetEntity=Policy.class, mappedBy="policyRoot", cascade=CascadeType.ALL)
#OrderColumn(name="policy_sequence", nullable=false)
public List<Policy> getPolicyList() {
return policyList;
}
public void setPolicyList(List<Policy> policyList) {
this.policyList = policyList;
}
public void addPolicy(Policy policy) {
policyList.add(policy);
policy.setPolicyRoot(this);
}
public void addPolicy(int sequence, Policy policy) {
policyList.add(sequence, policy);
policy.setPolicyRoot(this);
}
}
#Entity()
#Table(name="Policy")
public class Policy extends BaseDomainModel {
//No need to declare the policySequence field
/** Birectional pointer to parent */
private PolicyRoot policyRoot;
#Column(name="policy_sequence")
public int getPolicySequence() {
return policySequence;
}
public void setPolicySequence(int policySequence) {
this.policySequence = policySequence;
}
#ManyToOne
#JoinColumn(name="policy_root_oid", nullable=false)
public PolicyRoot getPolicyRoot() {
return policyRoot;
}
public void setPolicyRoot(PolicyRoot policyRoot) {
this.policyRoot = policyRoot;
}
}