Adds support for using MonetaryAmount in @ElementCollection

[Sarrruman]

Entity X containing @ElementCollection of type Y, where Y has a field of type MonetaryAmount, does not pass Hibernate's "metadata building" phase and raises following exception:

org.hibernate.MappingException: Could not instantiate collection persister implementor org.hibernate.persister.collection.BasicCollectionPersister for collection-role ...

[Sarrruman]

    @Entity(name = "Salary")
    @Table(name = "salary")
    public static class Salary {
        @Id
        @GeneratedValue
        private long id;

        private String other;

        @ElementCollection
        private List<SalaryComponent> components = new ArrayList<>();

        public long getId() {
            return id;
        }

        public void setId(long id) {
            this.id = id;
        }

        public List<SalaryComponent> getComponents() {
            return components;
        }

        public String getOther() {
            return other;
        }

        public void setOther(String other) {
            this.other = other;
        }
    }

    @Embeddable
    public static class SalaryComponent {
        @AttributeOverride(name = "amount", column = @Column(name = "salary_amount"))
        @AttributeOverride(name = "currency", column = @Column(name = "salary_currency"))
        @CompositeType(MonetaryAmountType.class)
        private MonetaryAmount value;

        public SalaryComponent(MonetaryAmount value) {
            this.value = value;
        }

        public SalaryComponent() {

        }

        public MonetaryAmount getValue() {
            return value;
        }

        public void setValue(MonetaryAmount value) {
            this.value = value;
        }
    }

[vladmihalcea]

Looking forward to your Pull Request that fixes the issue.

[Sarrruman]

Exception is raised because org.hibernate.cfg.PropertyContainer, which is responsible for the creation of metadata for the @Embeddable class, incorrectly constructs metadata for the embeddable type, because MonetaryAmountMapper doesn’t have getters&setters for its fields.

org.hibernate.cfg.PropertyContainer's contstructor is getting passed DEFAULT for defaultClassLevelAccessType parameter, which is then set to AccessType.PROPERTY, which results in PropertyContainer’s constructor relying on getters, instead of fields, for populating persistingAttributes.

In other cases (non-@ElementCollection ones), AccessLevel.FIELD is being passed in, thus not requiring MonetaryAmountMapper’s getters and resulting in correct mapping by Hibernate.

[vladmihalcea]

As I explained in my High-Performance Java Persistence book, @ElementCollection is a bad idea anyway.

So, you are better off using a bidirectional one-to-many where the MonetaryAmount is just a basic property in the child entity.

[Sarrruman]

I have a specific use-case: list, very short one, of value objects - something similar to the example I created in PostgreSQLMonetaryAmountTypeElementCollectionTest: Salary that is comprised of a couple of value components (VO in terms of DDD). They don't have their id etc..

[vladmihalcea]

Fixed.