Examples of oracle.toplink.essentials.queryframework.FetchGroup

Package oracle.toplink.essentials.queryframework

Examples of oracle.toplink.essentials.queryframework.FetchGroup

oracle.toplink.essentials.queryframework.FetchGroup

Purpose: A fetch group is a performance enhancement that allows a group of attributes of an object to be loaded on demand, which means that the data for an attribute might not loaded from the underlying data source until an explicit access call for the attribute first occurs. It avoids the wasteful practice of loading up all data of the object?s attributes, in which the user is interested in only partial of them. A great deal of caution and careful system use case analysis should be use when using the fetch group feature, as the extra round-trip would well offset the gain from the deferred loading in many cases. TopLink fetch group support is twofold: the pre-defined fetch groups at the descriptor level; and dynamic (use case) fetch groups at the query level. TopLink fetch group support is only on CMP project. Every query can has at most one fetch group. There is an optional pre-defined default fetch group at the descriptor level. If set, and the query has no fetch group being set, the default fetch group would be used, unless query.setShouldUseDefaultFetchGroup(false) is also called. In the latter case, the full object will be fetched after the query execution. @see oracle.toplink.essentials.queryframework.FetchGroup @see oracle.toplink.essentials.queryframework.FetchGroupTracker @author King Wang @since TopLink 10.1.3.

     * Return true if the object is partially fetched and cached.
     * It applies to the query with fetch group.
     */
    public boolean isPartialObject(Object domainObject) {
        if (domainObject != null) {
            FetchGroup fetchGroupInCache = ((FetchGroupTracker)domainObject).getFetchGroup();


            //if the fetch group reference is not null, it means the object is partial.
            return (fetchGroupInCache != null);
        }
        return false;

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    /**
     * INTERNAL:
     * Return if the cached object data is sufficiently valid against a fetch group
     */
    public boolean isObjectValidForFetchGroup(Object object, FetchGroup fetchGroup) {
        FetchGroup groupInObject = ((FetchGroupTracker)object).getFetchGroup();
        return (groupInObject == null) || groupInObject.isSupersetOf(fetchGroup);
    }

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     * Return true if the cached object data should be written in clone.
     * It is used in Fetch Group case when filling in the clone from the cached object.
     */
    public boolean shouldWriteInto(Object cachedObject, Object clone) {
        if (isPartialObject(clone)) {
            FetchGroup fetchGroupInSrc = ((FetchGroupTracker)cachedObject).getFetchGroup();
            FetchGroup fetchGroupInTarg = ((FetchGroupTracker)clone).getFetchGroup();


            //if the target fetch group is not null (i.e. fully fetched object) or if partially fetched, it's not a superset of that of the source, 
            //or if refresh is required, should always write (either refresh or revert) data from the cache to the clones.
            return (!((fetchGroupInTarg == null) || fetchGroupInTarg.isSupersetOf(fetchGroupInSrc)) || ((FetchGroupTracker)cachedObject).shouldRefreshFetchGroup());
        }
        return false;
    }

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    /**
    * INTERNAL:
    * Write data of the partially fetched object into the working and backup clones
    */
    public void writePartialIntoClones(Object partialObject, Object workingClone, UnitOfWorkImpl uow) {
        FetchGroup fetchGroupInClone = ((FetchGroupTracker)workingClone).getFetchGroup();
        FetchGroup fetchGroupInObject = ((FetchGroupTracker)partialObject).getFetchGroup();
        Object backupClone = uow.getBackupClone(workingClone);


        //if refresh is set, force to fill in fecth group data
        if (((FetchGroupTracker)partialObject).shouldRefreshFetchGroup()) {
            //refresh and fill in the fecth group data

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        //otherwise, union two fetch groups
        StringBuffer unionGroupName = new StringBuffer(first.getName());
        unionGroupName.append("_");
        unionGroupName.append(second.getName());
        FetchGroup unionFetchGroup = new FetchGroup(unionGroupName.toString());
        unionFetchGroup.addAttributes(first.getAttributes());
        unionFetchGroup.addAttributes(second.getAttributes());
        return unionFetchGroup;
    }

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    /**
     * Return true if the attribute of the object has already been fetched
     */
    public boolean isAttributeFetched(Object object, String attributeName) {
        FetchGroup fetchgroup = ((FetchGroupTracker)object).getFetchGroup();
        return (fetchgroup == null) || (fetchgroup.getAttributes().contains(attributeName));
    }

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Related Classes of oracle.toplink.essentials.queryframework.FetchGroup

oracle.toplink.essentials.descriptors.FetchGroupManager

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