package org.odmg;


/**
 * The base interface for all ODMG collections.
 * The ODMG collections are based on JavaSoft’s collection interfaces.
 * All of the operations defined by the JavaSoft <code>Collection</code>
 * interface are supported by an ODMG implementation of <code>DCollection</code>;
 * the exception <code>UnsupportedOperationException</code> is not thrown when a
 * call is made to any of the <code>Collection</code> methods.
 * <p>
 * <code>DCollection</code> contains methods used to perform queries on the collection.
 * The OQL query predicate is given as a string with the syntax of the
 * <code>where</code> clause of OQL. The predefined OQL variable <code>this</code>
 * is used inside the predicate to denote the current element of the collection.
 * @author	David Jordan (as Java Editor of the Object Data Management Group)
 * @version ODMG 3.0
 */
// * @see com.sun.java.util.collections.UnsupportedOperationException

public interface DCollection extends java.util.Collection
{
    /**
     * Selects the single element of the collection for which the provided OQL query
     * predicate is true.
     * @param	predicate	An OQL boolean query predicate.
     * @return The element that evaluates to true for the predicate. If no element
     * evaluates to true, null is returned.
     * @exception	QueryInvalidException	The query predicate is invalid.
     */
    public Object selectElement(String predicate) throws QueryInvalidException;

    /**
     * Access all of the elements of the collection that evaluate to true for the
     * provided query predicate.
     * @param	predicate	An OQL boolean query predicate.
     * @return	An iterator used to iterate over the elements that evaluated true for the predicate.
     * @exception	QueryInvalidException	The query predicate is invalid.
     */
    public java.util.Iterator select(String predicate) throws QueryInvalidException;

    /**
     * Evaluate the boolean query predicate for each element of the collection and
     * return a new collection that contains each element that evaluated to true.
     * @param	predicate	An OQL boolean query predicate.
     * @return	A new collection containing the elements that evaluated true for the predicate.
     * @exception	QueryInvalidException	The query predicate is invalid.
     */
    public DCollection query(String predicate) throws QueryInvalidException;

    /**
     * Determines whether there is an element of the collection that evaluates to true
     * for the predicate.
     * @param	predicate	An OQL boolean query predicate.
     * @return	True if there is an element of the collection that evaluates to true
     * for the predicate, otherwise false.
     * @exception	QueryInvalidException	The query predicate is invalid.
     */
    public boolean existsElement(String predicate) throws QueryInvalidException;
}