/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
 */
package org.hibernate.collection.spi;

import java.io.Serializable;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Collection;
import java.util.Iterator;

import org.hibernate.HibernateException;
import org.hibernate.engine.spi.SharedSessionContractImplementor;
import org.hibernate.loader.CollectionAliases;
import org.hibernate.persister.collection.CollectionPersister;
import org.hibernate.type.Type;

Persistent collections are treated as value objects by Hibernate.
ie. they have no independent existence beyond the object holding
a reference to them. Unlike instances of entity classes, they are
automatically deleted when unreferenced and automatically become
persistent when held by a persistent object. Collections can be
passed between different objects (change "roles") and this might
cause their elements to move from one database table to another.



Hibernate "wraps" a java collection in an instance of
PersistentCollection. This mechanism is designed to support
tracking of changes to the collection's persistent state and
lazy instantiation of collection elements. The downside is that
only certain abstract collection types are supported and any
extra semantics are lost



Applications should never use classes in this package
directly, unless extending the "framework" here.



Changes to structure of the collection are recorded by the
collection calling back to the session. Changes to mutable
elements (ie. composite elements) are discovered by cloning their
state when the collection is initialized and comparing at flush
time.
Author:
Gavin King/**
 * Persistent collections are treated as value objects by Hibernate.
 * ie. they have no independent existence beyond the object holding
 * a reference to them. Unlike instances of entity classes, they are
 * automatically deleted when unreferenced and automatically become
 * persistent when held by a persistent object. Collections can be
 * passed between different objects (change "roles") and this might
 * cause their elements to move from one database table to another.<br>
 * <br>
 * Hibernate "wraps" a java collection in an instance of
 * PersistentCollection. This mechanism is designed to support
 * tracking of changes to the collection's persistent state and
 * lazy instantiation of collection elements. The downside is that
 * only certain abstract collection types are supported and any
 * extra semantics are lost<br>
 * <br>
 * Applications should <em>never</em> use classes in this package
 * directly, unless extending the "framework" here.<br>
 * <br>
 * Changes to <em>structure</em> of the collection are recorded by the
 * collection calling back to the session. Changes to mutable
 * elements (ie. composite elements) are discovered by cloning their
 * state when the collection is initialized and comparing at flush
 * time.
 *
 * @author Gavin King
 */
public interface PersistentCollection {
	
Get the owning entity. Note that the owner is only
set during the flush cycle, and when a new collection
wrapper is created while loading an entity.
Returns:
The owner/**
	 * Get the owning entity. Note that the owner is only
	 * set during the flush cycle, and when a new collection
	 * wrapper is created while loading an entity.
	 *
	 * @return The owner
	 */
	Object getOwner();

	
Set the reference to the owning entity
Params:
entity – The owner/**
	 * Set the reference to the owning entity
	 *
	 * @param entity The owner
	 */
	void setOwner(Object entity);

	
Is the collection empty? (don't try to initialize the collection)
Returns:
false if the collection is non-empty; true otherwise./**
	 * Is the collection empty? (don't try to initialize the collection)
	 *
	 * @return {@code false} if the collection is non-empty; {@code true} otherwise.
	 */
	boolean empty();

	
After flushing, re-init snapshot state.
Params:
key – The collection instance key (fk value).
role – The collection role
snapshot – The snapshot state/**
	 * After flushing, re-init snapshot state.
	 *
	 * @param key The collection instance key (fk value).
	 * @param role The collection role
	 * @param snapshot The snapshot state
	 */
	void setSnapshot(Serializable key, String role, Serializable snapshot);

	
After flushing, clear any "queued" additions, since the
database state is now synchronized with the memory state.
/**
	 * After flushing, clear any "queued" additions, since the
	 * database state is now synchronized with the memory state.
	 */
	void postAction();
	
	
Return the user-visible collection (or array) instance
Returns:
The underlying collection/array/**
	 * Return the user-visible collection (or array) instance
	 *
	 * @return The underlying collection/array
	 */
	Object getValue();

	
Called just before reading any rows from the JDBC result set
/**
	 * Called just before reading any rows from the JDBC result set
	 */
	void beginRead();

	
Called after reading all rows from the JDBC result set
Returns:
Whether to end the read./**
	 * Called after reading all rows from the JDBC result set
	 *
	 * @return Whether to end the read.
	 */
	boolean endRead();
	
	
Called after initializing from cache
Returns:
??/**
	 * Called after initializing from cache
	 *
	 * @return ??
	 */
	boolean afterInitialize();

	
Could the application possibly have a direct reference to
the underlying collection implementation?
Returns:
true indicates that the application might have access to the underlying collection/array./**
	 * Could the application possibly have a direct reference to
	 * the underlying collection implementation?
	 *
	 * @return {@code true} indicates that the application might have access to the underlying collection/array.
	 */
	boolean isDirectlyAccessible();

	
Disassociate this collection from the given session.
Params:
currentSession – The session we are disassociating from.  Used for validations.
Returns:
true if this was currently associated with the given session/**
	 * Disassociate this collection from the given session.
	 *
	 * @param currentSession The session we are disassociating from.  Used for validations.
	 *
	 * @return true if this was currently associated with the given session
	 */
	boolean unsetSession(SharedSessionContractImplementor currentSession);

	
Associate the collection with the given session.
Params:
session – The session to associate with
Throws:
HibernateException – if the collection was already associated
with another open session
Returns:
false if the collection was already associated with the session/**
	 * Associate the collection with the given session.
	 *
	 * @param session The session to associate with
	 *
	 * @return false if the collection was already associated with the session
	 *
	 * @throws HibernateException if the collection was already associated
	 * with another open session
	 */
	boolean setCurrentSession(SharedSessionContractImplementor session) throws HibernateException;

	
Read the state of the collection from a disassembled cached value
Params:
persister – The collection persister
disassembled – The disassembled cached state
owner – The collection owner/**
	 * Read the state of the collection from a disassembled cached value
	 *
	 * @param persister The collection persister
	 * @param disassembled The disassembled cached state
	 * @param owner The collection owner
	 */
	void initializeFromCache(CollectionPersister persister, Serializable disassembled, Object owner);

	
Iterate all collection entries, during update of the database
Params:
persister – The collection persister.
Returns:
The iterator/**
	 * Iterate all collection entries, during update of the database
	 *
	 * @param persister The collection persister.
	 *
	 * @return The iterator
	 */
	Iterator entries(CollectionPersister persister);

	
Read a row from the JDBC result set
Params:
rs – The JDBC ResultSet
role – The collection role
descriptor – The aliases used for the columns making up the collection
owner – The collection owner
Throws:
HibernateException – Generally indicates a problem resolving data read from the ResultSet
SQLException – Indicates a problem accessing the ResultSet
Returns:
The read object/**
	 * Read a row from the JDBC result set
	 *
	 * @param rs The JDBC ResultSet
	 * @param role The collection role
	 * @param descriptor The aliases used for the columns making up the collection
	 * @param owner The collection owner
	 *
	 * @return The read object
	 *
	 * @throws HibernateException Generally indicates a problem resolving data read from the ResultSet
	 * @throws SQLException Indicates a problem accessing the ResultSet
	 */
	Object readFrom(ResultSet rs, CollectionPersister role, CollectionAliases descriptor, Object owner)
			throws HibernateException, SQLException;

	
Get the identifier of the given collection entry. This refers to the collection identifier, not the identifier of the (possibly) entity elements. This is only valid for invocation on the idbag collection. 
Params:
entry – The collection entry/element
i – The assumed identifier (?)
Returns:
The identifier value/**
	 * Get the identifier of the given collection entry.  This refers to the collection identifier, not the
	 * identifier of the (possibly) entity elements.  This is only valid for invocation on the
	 * {@code idbag} collection.
	 *
	 * @param entry The collection entry/element
	 * @param i The assumed identifier (?)
	 *
	 * @return The identifier value
	 */
	Object getIdentifier(Object entry, int i);
	
	
Get the index of the given collection entry
Params:
entry – The collection entry/element
i – The assumed index
persister – it was more elegant before we added this...
Returns:
The index value/**
	 * Get the index of the given collection entry
	 *
	 * @param entry The collection entry/element
	 * @param i The assumed index
	 * @param persister it was more elegant before we added this...
	 *
	 * @return The index value
	 */
	Object getIndex(Object entry, int i, CollectionPersister persister);
	
	
Get the value of the given collection entry.  Generally the given entry parameter value will just be returned.
Might get a different value for a duplicate entries in a Set.
Params:
entry – The object instance for which to get the collection element instance.
Returns:
The corresponding object that is part of the collection elements./**
	 * Get the value of the given collection entry.  Generally the given entry parameter value will just be returned.
	 * Might get a different value for a duplicate entries in a Set.
	 *
	 * @param entry The object instance for which to get the collection element instance.
	 *
	 * @return The corresponding object that is part of the collection elements.
	 */
	Object getElement(Object entry);
	
	
Get the snapshot value of the given collection entry
Params:
entry – The entry
i – The index
Returns:
The snapshot state for that element/**
	 * Get the snapshot value of the given collection entry
	 *
	 * @param entry The entry
	 * @param i The index
	 *
	 * @return The snapshot state for that element
	 */
	Object getSnapshotElement(Object entry, int i);

	
Called before any elements are read into the collection,
allowing appropriate initializations to occur.
Params:
persister – The underlying collection persister.
anticipatedSize – The anticipated size of the collection after initialization is complete./**
	 * Called before any elements are read into the collection,
	 * allowing appropriate initializations to occur.
	 *
	 * @param persister The underlying collection persister.
	 * @param anticipatedSize The anticipated size of the collection after initialization is complete.
	 */
	void beforeInitialize(CollectionPersister persister, int anticipatedSize);

	
Does the current state exactly match the snapshot?
Params:
persister – The collection persister
Returns:
true if the current state and the snapshot state match./**
	 * Does the current state exactly match the snapshot?
	 *
	 * @param persister The collection persister
	 *
	 * @return {@code true} if the current state and the snapshot state match.
	 *
	 */
	boolean equalsSnapshot(CollectionPersister persister);

	
Is the snapshot empty?
Params:
snapshot – The snapshot to check
Returns:
true if the given snapshot is empty/**
	 * Is the snapshot empty?
	 *
	 * @param snapshot The snapshot to check
	 *
	 * @return {@code true} if the given snapshot is empty
	 */
	boolean isSnapshotEmpty(Serializable snapshot);
	
	
Disassemble the collection to get it ready for the cache
Params:
persister – The collection persister
Returns:
The disassembled state/**
	 * Disassemble the collection to get it ready for the cache
	 *
	 * @param persister The collection persister
	 *
	 * @return The disassembled state
	 */
	Serializable disassemble(CollectionPersister persister) ;

	
Do we need to completely recreate this collection when it changes?
Params:
persister – The collection persister
Returns:
true if a change requires a recreate./**
	 * Do we need to completely recreate this collection when it changes?
	 *
	 * @param persister The collection persister
	 *
	 * @return {@code true} if a change requires a recreate.
	 */
	boolean needsRecreate(CollectionPersister persister);

	
Return a new snapshot of the current state of the collection
Params:
persister – The collection persister
Returns:
The snapshot/**
	 * Return a new snapshot of the current state of the collection
	 *
	 * @param persister The collection persister
	 *
	 * @return The snapshot
	 */
	Serializable getSnapshot(CollectionPersister persister);

	
To be called internally by the session, forcing immediate initialization.
/**
	 * To be called internally by the session, forcing immediate initialization.
	 */
	void forceInitialization();

	
Does the given element/entry exist in the collection?
Params:
entry – The object to check if it exists as a collection element
i – Unused
Returns:
true if the given entry is a collection element/**
	 * Does the given element/entry exist in the collection?
	 *
	 * @param entry The object to check if it exists as a collection element
	 * @param i Unused
	 *
	 * @return {@code true} if the given entry is a collection element
	 */
	boolean entryExists(Object entry, int i);

	
Do we need to insert this element?
Params:
entry – The collection element to check
i – The index (for indexed collections)
elemType – The type for the element
Returns:
true if the element needs inserting/**
	 * Do we need to insert this element?
	 *
	 * @param entry The collection element to check
	 * @param i The index (for indexed collections)
	 * @param elemType The type for the element
	 *
	 * @return {@code true} if the element needs inserting
	 */
	boolean needsInserting(Object entry, int i, Type elemType);

	
Do we need to update this element?
Params:
entry – The collection element to check
i – The index (for indexed collections)
elemType – The type for the element
Returns:
true if the element needs updating/**
	 * Do we need to update this element?
	 *
	 * @param entry The collection element to check
	 * @param i The index (for indexed collections)
	 * @param elemType The type for the element
	 *
	 * @return {@code true} if the element needs updating
	 */
	boolean needsUpdating(Object entry, int i, Type elemType);

	
Can each element in the collection be mapped unequivocally to a single row in the database?  Generally
bags and sets are the only collections that cannot be.
Returns:
true if the row for each element is known/**
	 * Can each element in the collection be mapped unequivocally to a single row in the database?  Generally
	 * bags and sets are the only collections that cannot be.
	 *
	 * @return {@code true} if the row for each element is known
	 */
	boolean isRowUpdatePossible();

	
Get all the elements that need deleting
Params:
persister – The collection persister
indexIsFormula – For indexed collections, tells whether the index is a formula (calculated value) mapping
Returns:
An iterator over the elements to delete/**
	 * Get all the elements that need deleting
	 *
	 * @param persister The collection persister
	 * @param indexIsFormula For indexed collections, tells whether the index is a formula (calculated value) mapping
	 *
	 * @return An iterator over the elements to delete
	 */
	Iterator getDeletes(CollectionPersister persister, boolean indexIsFormula);

	
Is this the wrapper for the given collection instance?
Params:
collection – The collection to check whether this is wrapping it
Returns:
 true if this is a wrapper around that given collection instance./**
	 * Is this the wrapper for the given collection instance?
	 *
	 * @param collection The collection to check whether this is wrapping it
	 *
	 * @return  {@code true} if this is a wrapper around that given collection instance.
	 */
	boolean isWrapper(Object collection);

	
Is this instance initialized?
Returns:
Was this collection initialized?  Or is its data still not (fully) loaded?/**
	 * Is this instance initialized?
	 *
	 * @return Was this collection initialized?  Or is its data still not (fully) loaded?
	 */
	boolean wasInitialized();

	
Does this instance have any "queued" operations?
Returns:
true indicates there are pending, queued, delayed operations/**
	 * Does this instance have any "queued" operations?
	 *
	 * @return {@code true} indicates there are pending, queued, delayed operations
	 */
	boolean hasQueuedOperations();

	
Iterator over the "queued" additions
Returns:
The iterator/**
	 * Iterator over the "queued" additions
	 *
	 * @return The iterator
	 */
	Iterator queuedAdditionIterator();
	
	
Get the "queued" orphans
Params:
entityName – The name of the entity that makes up the elements
Returns:
The orphaned elements/**
	 * Get the "queued" orphans
	 *
	 * @param entityName The name of the entity that makes up the elements
	 *
	 * @return The orphaned elements
	 */
	Collection getQueuedOrphans(String entityName);
	
	
Get the current collection key value
Returns:
the current collection key value/**
	 * Get the current collection key value
	 *
	 * @return the current collection key value
	 */
	Serializable getKey();
	
	
Get the current role name
Returns:
the collection role name/**
	 * Get the current role name
	 *
	 * @return the collection role name
	 */
	String getRole();
	
	
Is the collection unreferenced?
Returns:
true if the collection is no longer referenced by an owner/**
	 * Is the collection unreferenced?
	 *
	 * @return {@code true} if the collection is no longer referenced by an owner
	 */
	boolean isUnreferenced();
	
	
Is the collection dirty? Note that this is only
reliable during the flush cycle, after the
collection elements are dirty checked against
the snapshot.
Returns:
true if the collection is dirty/**
	 * Is the collection dirty? Note that this is only
	 * reliable during the flush cycle, after the
	 * collection elements are dirty checked against
	 * the snapshot.
	 *
	 * @return {@code true} if the collection is dirty
	 */
	boolean isDirty();

	default boolean isElementRemoved(){
		return false;
	}

	
Clear the dirty flag, after flushing changes
to the database.
/**
	 * Clear the dirty flag, after flushing changes
	 * to the database.
	 */
	void clearDirty();
	
	
Get the snapshot cached by the collection instance
Returns:
The internally stored snapshot state/**
	 * Get the snapshot cached by the collection instance
	 *
	 * @return The internally stored snapshot state
	 */
	Serializable getStoredSnapshot();
	
	
Mark the collection as dirty
/**
	 * Mark the collection as dirty
	 */
	void dirty();
	
	
Called before inserting rows, to ensure that any surrogate keys
are fully generated
Params:
persister – The collection persister/**
	 * Called before inserting rows, to ensure that any surrogate keys
	 * are fully generated
	 *
	 * @param persister The collection persister
	 */
	void preInsert(CollectionPersister persister);

	
Called after inserting a row, to fetch the natively generated id
Params:
persister – The collection persister
entry – The collection element just inserted
i – The element position/index/**
	 * Called after inserting a row, to fetch the natively generated id
	 *
	 * @param persister The collection persister
	 * @param entry The collection element just inserted
	 * @param i The element position/index
	 */
	void afterRowInsert(CollectionPersister persister, Object entry, int i);

	
get all "orphaned" elements
Params:
snapshot – The snapshot state
entityName – The name of the entity that are the elements of the collection
Returns:
The orphans/**
	 * get all "orphaned" elements
	 *
	 * @param snapshot The snapshot state
	 * @param entityName The name of the entity that are the elements of the collection
	 *
	 * @return The orphans
	 */
	Collection getOrphans(Serializable snapshot, String entityName);
	
}