Qtn Reg EJBQL in HFEJB.

[Natarajan Shankar]

Hello All,
In the HFEJB - 429. Qtn - 15.

Option 2 says the Identification vaiable can represent a single variable or a collection
-- It is corerct right, since we can use it like
WHERE m.title='some title' and
WHERE d.movies IS EMPTY.

Pls. Clarify my understanding is wrong or not.

[Sandesh Tathare]

Shankar,

An identification variable designates an instance of an entity bean abstract schema type or an element of a collection of entity bean abstract schema types instances.

An identification variable thus always designates a reference to a single value. It is declared in one of two ways; as a range variable or a collection member identification variable:

1. A range variable is declared using the abstract schema name of an entity bean
2. A collection member identification variable is declared using a collection-valued path expression.

For Example:

 
SELECT DISTINCT OBJECT(o)
FROM Order o, IN(o.lineItems) l
WHERE l.product.product_type = �office_supplies�

In the FROM clause declaration IN(o.lineItems) l, the identification variable l evaluates to any LineItem value directly reachable from Order.

The cmr-field lineItems is a collection of instances of the abstract schema type LineItem and the identification variable l refers to an element of this collection. The type of l is the abstract schema type of LineItem.

Hope this clarifies it.