org.jsimpledb.change.ChangeCopier Maven / Gradle / Ivy

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/*
 * Copyright (C) 2015 Archie L. Cobbs. All rights reserved.
 */

package org.jsimpledb.change;

import com.google.common.base.Preconditions;

import org.jsimpledb.CopyState;
import org.jsimpledb.JObject;
import org.jsimpledb.JTransaction;

/**
 * Creates a new {@link Change} object based on an existing one where the {@link JObject}s referred to by the
 * new {@link Change} are copies in a different transaction of the originals. This is useful to allow database
 * change information to be accessed after the transaction in which the change occured has completed.
 *
 * 
 * Each instance has an internal {@link CopyState} used to avoid redundant copies, accessible via {@link #getCopyState}.
 */
public class ChangeCopier implements ChangeSwitch> {

    protected final JTransaction dest;
    protected final CopyState copyState = new CopyState();

    /**
     * Primary constructor.
     *
     * @param dest destination transaction for copied {@link JObject}s
     * @throws IllegalArgumentException if {@code dest} is null
     */
    public ChangeCopier(JTransaction dest) {
        Preconditions.checkArgument(dest != null, "null dest");
        this.dest = dest;
    }

    /**
     * "Snapshot" constructor for when the destination transaction is the "snapshot" transaction of the transaction
     * associated with the current thread.
     *
     * 

     * This is a convenience constructor, equivalent to:
     * 

     * ChangeCopier(JTransaction.getCurrent().getSnapshotTransaction())
     * 
     *
     * @throws IllegalStateException if this is not a snapshot instance and there is no {@link JTransaction}
     *  associated with the current thread
     */
    public ChangeCopier() {
        this(JTransaction.getCurrent().getSnapshotTransaction());
    }

    /**
     * Get the destination transaction configured in this instance.
     *
     * @return destination transaction
     */
    public JTransaction getDestinationTransaction() {
        return this.dest;
    }

    /**
     * Get the {@link CopyState} used by this instance.
     *
     * @return associated copy state
     */
    public CopyState getCopyState() {
        return this.copyState;
    }

    @Override
    public  ObjectCreate caseObjectCreate(ObjectCreate change) {
        return new ObjectCreate(this.copyIfReference(change.getObject()));
    }

    @Override
    public  ObjectDelete caseObjectDelete(ObjectDelete change) {
        return new ObjectDelete(this.copyIfReference(change.getObject()));
    }

    @Override
    public  ListFieldAdd caseListFieldAdd(ListFieldAdd change) {
        return new ListFieldAdd(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName(),
          change.getIndex(), this.copyIfReference(change.getElement()));
    }

    @Override
    public  ListFieldClear caseListFieldClear(ListFieldClear change) {
        return new ListFieldClear(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName());
    }

    @Override
    public  ListFieldRemove caseListFieldRemove(ListFieldRemove change) {
        return new ListFieldRemove(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName(),
          change.getIndex(), this.copyIfReference(change.getElement()));
    }

    @Override
    public  ListFieldReplace caseListFieldReplace(ListFieldReplace change) {
        return new ListFieldReplace(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName(),
          change.getIndex(), this.copyIfReference(change.getOldValue()), this.copyIfReference(change.getNewValue()));
    }

    @Override
    public  MapFieldAdd caseMapFieldAdd(MapFieldAdd change) {
        return new MapFieldAdd(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName(),
          this.copyIfReference(change.getKey()), this.copyIfReference(change.getValue()));
    }

    @Override
    public  MapFieldClear caseMapFieldClear(MapFieldClear change) {
        return new MapFieldClear(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName());
    }

    @Override
    public  MapFieldRemove caseMapFieldRemove(MapFieldRemove change) {
        return new MapFieldRemove(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName(),
          this.copyIfReference(change.getKey()), this.copyIfReference(change.getValue()));
    }

    @Override
    public  MapFieldReplace caseMapFieldReplace(MapFieldReplace change) {
        return new MapFieldReplace(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName(),
          this.copyIfReference(change.getKey()), this.copyIfReference(change.getOldValue()),
          this.copyIfReference(change.getNewValue()));
    }

    @Override
    public  SetFieldAdd caseSetFieldAdd(SetFieldAdd change) {
        return new SetFieldAdd(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName(),
          this.copyIfReference(change.getElement()));
    }

    @Override
    public  SetFieldClear caseSetFieldClear(SetFieldClear change) {
        return new SetFieldClear(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName());
    }

    @Override
    public  SetFieldRemove caseSetFieldRemove(SetFieldRemove change) {
        return new SetFieldRemove(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName(),
          this.copyIfReference(change.getElement()));
    }

    @Override
    public  SimpleFieldChange caseSimpleFieldChange(SimpleFieldChange change) {
        return new SimpleFieldChange(this.copyIfReference(change.getObject()), change.getStorageId(), change.getFieldName(),
          this.copyIfReference(change.getOldValue()), this.copyIfReference(change.getNewValue()));
    }

    @SuppressWarnings("unchecked")
    private  T copyIfReference(T obj) {
        return obj instanceof JObject ? (T)this.copy((JObject)obj) : obj;
    }

    /**
     * Copy the given {@link JObject} into the destination transaction.
     *
     * 
     * The implementation in {@link ChangeCopier} invokes {@code jobj.copyTo(this.dest, null, this.getCopyState())} unless
     * {@code jobj} does not exist, in which case it is not copied (but the
     * {@linkplain JTransaction#get(ObjId) corresponding} {@link JObject} is still returned).
     * Subclasses may override to copy additional objects referenced by {@code jobj} as needed.
     *
     * @param jobj original object
     * @return copied object in {@link #dest}
     * @throws IllegalArgumentException if {@code jobj} is null
     */
    @SuppressWarnings("unchecked")
    protected JObject copy(JObject jobj) {
        Preconditions.checkArgument(jobj != null, "null jobj");
        return !jobj.exists() ? this.dest.get(jobj) : jobj.copyTo(this.dest, null, this.getCopyState());
    }
}