12.4.8. About Qualified Path Expressions

It was previously stated that collection-valued associations actually refer to the values of that collection. Based on the type of collection, there are also available a set of explicit qualification expressions.

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Table 12.9. Qualified Path Expressions
Expression	Description
`VALUE`	Refers to the collection value. Same as not specifying a qualifier. Useful to explicitly show intent. Valid for any type of collection-valued reference.
`INDEX`	According to HQL rules, this is valid for both Maps and Lists which specify a `javax.persistence.OrderColumn` annotation to refer to the Map key or the List position (aka the OrderColumn value). JPQL however, reserves this for use in the List case and adds `KEY` for the MAP case. Applications interested in JPA provider portability should be aware of this distinction.
`KEY`	Valid only for Maps. Refers to the map's key. If the key is itself an entity, can be further navigated.
`ENTRY`	Only valid only for Maps. Refers to the Map's logical `java.util.Map.Entry` tuple (the combination of its key and value). `ENTRY` is only valid as a terminal path and only valid in the select clause.

Example 12.9. Qualified Collection References Example

// Product.images is a Map<String,String> : key = a name, value = file path

// select all the image file paths (the map value) for Product#123
select i
from Product p
    join p.images i
where p.id = 123

// same as above
select value(i)
from Product p
    join p.images i
where p.id = 123

// select all the image names (the map key) for Product#123
select key(i)
from Product p
    join p.images i
where p.id = 123

// select all the image names and file paths (the 'Map.Entry') for Product#123
select entry(i)
from Product p
    join p.images i
where p.id = 123

// total the value of the initial line items for all orders for a customer
select sum( li.amount )
from Customer c
        join c.orders o
        join o.lineItems li
where c.id = 123
  and index(li) = 1

// Product.images is a Map<String,String> : key = a name, value = file path

// select all the image file paths (the map value) for Product#123
select i
from Product p
    join p.images i
where p.id = 123

// same as above
select value(i)
from Product p
    join p.images i
where p.id = 123

// select all the image names (the map key) for Product#123
select key(i)
from Product p
    join p.images i
where p.id = 123

// select all the image names and file paths (the 'Map.Entry') for Product#123
select entry(i)
from Product p
    join p.images i
where p.id = 123

// total the value of the initial line items for all orders for a customer
select sum( li.amount )
from Customer c
        join c.orders o
        join o.lineItems li
where c.id = 123
  and index(li) = 1

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12.4.8. About Qualified Path Expressions

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