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  package org.apache.cayenne.lifecycle.relationship;
  
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import org.apache.cayenne.Cayenne;
  import org.apache.cayenne.ObjectContext;
  import org.apache.cayenne.ObjectId;
  import org.apache.cayenne.Persistent;
  import org.apache.cayenne.exp.Expression;
  import org.apache.cayenne.exp.ExpressionFactory;
  import org.apache.cayenne.lifecycle.id.EntityIdCoder;
  import org.apache.cayenne.map.EntityResolver;
  import org.apache.cayenne.map.ObjEntity;
  import org.apache.cayenne.query.ObjectIdQuery;
  import org.apache.cayenne.query.ObjectSelect;
  
  /**
   * Provides lazy faulting functionality for a map of objects identified by
   * String ObjectId.
   * 
   * @since 3.1
   */
  class ObjectIdBatchFault {
  
  	private ObjectContext context;
  	private List<ObjectIdBatchSourceItem> sources;
  	private volatile Map<String, Object> resolved;
  
  	ObjectIdBatchFault(ObjectContext context, List<ObjectIdBatchSourceItem> sources) {
  		this.context = context;
  		this.sources = sources;
  	}
  
  	Map<String, Object> getObjects() {
  
  		if (resolved == null) {
  
  			synchronized (this) {
  
  				if (resolved == null) {
  					resolved = fetchObjects();
  				}
  			}
  		}
  
  		return resolved;
  	}
  
  	private Map<String, Object> fetchObjects() {
  
  		if (sources == null) {
  			return Collections.emptyMap();
  		}
  
  		EntityResolver resolver = context.getEntityResolver();
  
  		// simple case of one query, handle it separately for performance
  		// reasons
  		if (sources.size() == 1) {
  
  			String uuid = sources.get(0).getId();
  			String entityName = EntityIdCoder.getEntityName(uuid);
  
  			ObjEntity entity = resolver.getObjEntity(entityName);
  			ObjectId id = new EntityIdCoder(entity).toObjectId(uuid);
  
  			Object object = Cayenne.objectForQuery(context, new ObjectIdQuery(id));
  			if (object == null) {
  				return Collections.emptyMap();
  			} else {
  				return Collections.singletonMap(uuid, object);
  			}
  		}
  
  		Map<String, ObjectSelect<Persistent>> queriesByEntity = new HashMap<>();
  		Map<String, EntityIdCoder> codersByEntity = new HashMap<>();
  
  		for (ObjectIdBatchSourceItem source : sources) {
  
  			String uuid = source.getId();
  			String entityName = EntityIdCoder.getEntityName(uuid);
  			EntityIdCoder coder = codersByEntity.get(entityName);
  			ObjectSelect<Persistent> query;
  
  			if (coder == null) {
  				coder = new EntityIdCoder(resolver.getObjEntity(entityName));
  				codersByEntity.put(entityName, coder);
  
  				query = ObjectSelect.query(Persistent.class, entityName);
  				queriesByEntity.put(entityName, query);
  			} else {
  				query = queriesByEntity.get(entityName);
  			}
  
  			ObjectId id = coder.toObjectId(uuid);
  			Expression idExp = ExpressionFactory.matchAllDbExp(id.getIdSnapshot(), Expression.EQUAL_TO);
  			query.or(idExp);
  		}
  
  		int capacity = (int) Math.ceil(sources.size() / 0.75d);
  		Map<String, Object> results = new HashMap<>(capacity);
  
  		for (ObjectSelect<Persistent> query : queriesByEntity.values()) {
  			EntityIdCoder coder = codersByEntity.get(query.getEntityName());
  			List<Persistent> objects = query.select(context);
  			for (Persistent object : objects) {
  				String uuid = coder.toStringId(object.getObjectId());
  				results.put(uuid, object);
  			}
  		}
  
  		return results;
  	}
  }
  