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CollectionChangeDetector.java
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CollectionChangeDetector.java
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/**
* Copyright (C) 2022 Czech Technical University in Prague
*
* This program is free software: you can redistribute it and/or modify it under
* the terms of the GNU General Public License as published by the Free Software
* Foundation, either version 3 of the License, or (at your option) any
* later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
* details. You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package cz.cvut.kbss.jopa.sessions.change;
import cz.cvut.kbss.jopa.sessions.MetamodelProvider;
import cz.cvut.kbss.jopa.utils.EntityPropertiesUtils;
import java.util.*;
/**
* Checks for changes in a collection. By changes it is understood:
* <pre>
* <ul>
* <li>Different number of elements,</li>
* <li>Different order of elements in a collection with deterministic ordering semantics (List, Queue,
* <b>NOT!</b> Set)</li>
* <li>Different elements in the collection</li>
* </ul>
* </pre>
*/
class CollectionChangeDetector implements ChangeDetector {
private final ChangeDetector changeDetector;
private final MetamodelProvider metamodelProvider;
CollectionChangeDetector(ChangeDetector changeDetector, MetamodelProvider metamodelProvider) {
this.changeDetector = changeDetector;
this.metamodelProvider = metamodelProvider;
}
@Override
public boolean hasChanges(Object clone, Object original) {
assert clone != null;
assert original != null;
Collection<?> origCol = (Collection<?>) original;
Collection<?> cloneCol = (Collection<?>) clone;
if (origCol.size() != cloneCol.size()) {
return true;
}
if (origCol.isEmpty()) {
return false;
}
if (origCol instanceof Set) {
return setChanged(cloneCol, origCol);
} else {
return orderedCollectionChanged(cloneCol, origCol);
}
}
private boolean orderedCollectionChanged(Collection<?> clone, Collection<?> original) {
Iterator<?> itOrig = original.iterator();
Iterator<?> itClone = clone.iterator();
boolean changes = false;
while (itOrig.hasNext() && !changes) {
final Object cl = itClone.next();
final Object orig = itOrig.next();
changes = changeDetector.hasChanges(cl, orig);
}
return changes;
}
/**
* When checking for set changes, we have to make sure different element order does not mean a change.
* <p>
* Therefore, we first order the elements in a predictable way and then compare the elements.
*/
private boolean setChanged(Collection<?> clone, Collection<?> original) {
assert !clone.isEmpty();
assert !original.isEmpty();
final Class<?> elementType = clone.iterator().next().getClass();
final List<?> cloneList = new ArrayList<>(clone);
final Comparator<Object> comparator = getSetComparator(elementType);
cloneList.sort(comparator);
final List<?> originalList = new ArrayList<>(original);
originalList.sort(comparator);
return orderedCollectionChanged(cloneList, originalList);
}
/**
* For managed types, the comparator uses identifier's hashCode, for all other types hashCode is used directly.
*/
private Comparator<Object> getSetComparator(Class<?> elemType) {
if (metamodelProvider.isEntityType(elemType)) {
return (o1, o2) -> {
final Object keyOne = EntityPropertiesUtils.getIdentifier(o1, metamodelProvider.getMetamodel());
final Object keyTwo = EntityPropertiesUtils.getIdentifier(o2, metamodelProvider.getMetamodel());
if (keyOne == null || keyTwo == null) {
return 0;
}
return Integer.compare(keyOne.hashCode(), keyTwo.hashCode());
};
} else {
return Comparator.comparingInt(Object::hashCode);
}
}
}