How to access Map field in JPA via JPQL

Question

for example, if there is an @ElementCollection file which is with a Map type, then if I try to get the map key or value field then how to process?

Class Deal{
.....

private String name;

private String department;

private DealType type;

@AttributeOverrides({
    @AttributeOverride(name="value.in.available", column=@Column(name="in_avl")),
    @AttributeOverride(name="value.in.unavailable", column=@Column(name="in_unv")),
    @AttributeOverride(name="value.out.available", column=@Column(name="out_avl")),
    @AttributeOverride(name="value.out.unavailable", column=@Column(name="out_unv"))
})
@ElementCollection(fetch = FetchType.EAGER)
    ......
}

So if I try to get something like this

select new SummaryAmount(SUM(t.value.in.available), SUM(t.value.in.unavailable),
SUM(t.value.out.available), SUM(t.value.out.unavailable)) from Deal AS d INNER 
JOIN d.transactionAmounts t GROUP by t.key;

Is it something possible can work out now? Everything is follow the book except I invent the t.value and t.key as I really don't know how to present map key and value in JPQL.Thanks

Thanks

Answer 1

Try this:

SELECT new SummaryAmount(SUM(VALUE(t).in.available), SUM(VALUE(t)in.unavailable),
SUM(VALUE(t).out.available), SUM(VALUE(t).out.unavailable)) from Deal AS d INNER 
JOIN d.transactionAmounts t GROUP by KEY(t);

And now an excerpt from the JPA specification:

An identification variable qualified by the KEY, VALUE, or ENTRY operator is a path expression. The KEY, VALUE, and ENTRY operators may only be applied to identification variables that correspond to map-valued associations or map-valued element collections. The type of the path expression is the type computed as the result of the operation; that is, the abstract schema type of the field that is the value of the KEY, VALUE, or ENTRY operator (the map key, map value, or map entry respectively).[53]

The syntax for qualified identification variables is as follows.

qualified_identification_variable :: =

KEY(identification_variable) |

VALUE(identification_variable) |

ENTRY(identification_variable)

A path expression using the KEY or VALUE operator can be further composed. A path expression using the ENTRY operator is terminal. It cannot be further composed and can only appear in the SELECT list of a query.