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* to you under the Apache License, Version 2.0 (the
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* http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.cayenne.configuration;
import org.apache.cayenne.map.DataMap;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A default implementation of {@link DataChannelDescriptorMerger}. The general rule of
* merge is that the order of descriptors on the merge list matters. If there are two
* conflicting metadata objects belonging to two descriptors, an object from the last
* descriptor takes precedence over the object from the first one. This way it is easy to
* override pieces of metadata. This is also similar to how DI modules are merged in
* Cayenne. So this is how the merge works:
* <ul>
* <li>Merged descriptor name is the same as the name of the last descriptor on the merge
* list.</li>
* <li>Merged descriptor properties are the same as the properties of the last descriptor
* on the merge list. I.e. properties are not merged to avoid invalid combinations and
* unexpected runtime behavior.</li>
* <li>If there are two or more DataMaps with the same name, only one DataMap is placed in
* the merged descriptor, the rest are discarded. DataMap with highest index in the
* descriptor array is chosen per precedence rule above.</li>
* <li>If there are two or more DataNodes with the same name, only one DataNodes is placed
* in the merged descriptor, the rest are discarded. DataNodes with highest index in the
* descriptor array is chosen per precedence rule above.</li>
* </ul>
*
* @since 3.1
*/
public class DefaultDataChannelDescriptorMerger implements DataChannelDescriptorMerger {
private static Logger logger = LoggerFactory
.getLogger(DefaultDataChannelDescriptorMerger.class);
public DataChannelDescriptor merge(DataChannelDescriptor... descriptors) {
if (descriptors == null || descriptors.length == 0) {
throw new IllegalArgumentException("Null or empty descriptors");
}
if (descriptors.length == 1) {
return descriptors[0];
}
int len = descriptors.length;
// merge into a new descriptor; do not alter source descriptors
DataChannelDescriptor merged = new DataChannelDescriptor();
merged.setName(descriptors[len - 1].getName());
merged.getProperties().putAll(descriptors[len - 1].getProperties());
// iterate in reverse order to reduce add/remove operations
for (int i = len - 1; i >= 0; i--) {
DataChannelDescriptor descriptor = descriptors[i];
// DataMaps are merged by reference, as we don't change them
// TODO: they still have a link to the unmerged descriptor, is it bad?
for (DataMap map : descriptor.getDataMaps()) {
// report conflicting DataMap and leave the existing copy
DataMap existing = merged.getDataMap(map.getName());
if (existing != null) {
logger.info("Discarding overridden DataMap '"
+ map.getName()
+ "' from descriptor '"
+ descriptor.getName()
+ "'");
}
else {
logger.info("Using DataMap '"
+ map.getName()
+ "' from descriptor '"
+ descriptor.getName()
+ "' in merged descriptor");
merged.getDataMaps().add(map);
}
}
// DataNodes are merged by copy as we may modify them (changing map linking)
for (DataNodeDescriptor node : descriptor.getNodeDescriptors()) {
DataNodeDescriptor existing = merged.getNodeDescriptor(node.getName());
if (existing != null) {
logger.info("Discarding overridden DataNode '"
+ node.getName()
+ "' from descriptor '"
+ descriptor.getName()
+ "'");
for (String mapName : node.getDataMapNames()) {
if (!existing.getDataMapNames().contains(mapName)) {
existing.getDataMapNames().add(mapName);
}
}
}
else {
logger.info("Using DataNode '"
+ node.getName()
+ "' from descriptor '"
+ descriptor.getName()
+ "' in merged descriptor");
merged
.getNodeDescriptors()
.add(cloneDataNodeDescriptor(node, merged));
}
}
}
return merged;
}
protected DataNodeDescriptor cloneDataNodeDescriptor(
DataNodeDescriptor original,
DataChannelDescriptor targetOwner) {
DataNodeDescriptor clone = new DataNodeDescriptor(original.getName());
// do not clone 'configurationSource' as we may change the structure of the node
clone.setAdapterType(original.getAdapterType());
clone.setDataChannelDescriptor(targetOwner);
clone.setDataSourceDescriptor(original.getDataSourceDescriptor());
clone.setDataSourceFactoryType(original.getDataSourceFactoryType());
clone.setParameters(original.getParameters());
clone.setSchemaUpdateStrategyType(original.getSchemaUpdateStrategyType());
clone.getDataMapNames().addAll(original.getDataMapNames());
return clone;
}
}