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https://issues.apache.org/jira/browse/RYA-416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16308840#comment-16308840
]
ASF GitHub Bot commented on RYA-416:
------------------------------------
Github user kchilton2 commented on a diff in the pull request:
https://github.com/apache/incubator-rya/pull/254#discussion_r159333249
--- Diff:
dao/mongodb.rya/src/main/java/org/apache/rya/mongodb/aggregation/PipelineResultIteration.java
---
@@ -0,0 +1,132 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.rya.mongodb.aggregation;
+
+import java.util.Map;
+
+import org.bson.Document;
+import org.openrdf.model.Value;
+import org.openrdf.model.ValueFactory;
+import org.openrdf.model.impl.ValueFactoryImpl;
+import org.openrdf.model.vocabulary.XMLSchema;
+import org.openrdf.query.Binding;
+import org.openrdf.query.BindingSet;
+import org.openrdf.query.QueryEvaluationException;
+import org.openrdf.query.algebra.evaluation.QueryBindingSet;
+
+import com.mongodb.client.AggregateIterable;
+import com.mongodb.client.MongoCursor;
+
+import info.aduna.iteration.CloseableIteration;
+
+/**
+ * An iterator that converts the documents resulting from an
+ * {@link AggregationPipelineQueryNode} into {@link BindingSet}s.
+ */
+public class PipelineResultIteration implements
CloseableIteration<BindingSet, QueryEvaluationException> {
+ private static final int BATCH_SIZE = 1000;
+ private static final ValueFactory VF = ValueFactoryImpl.getInstance();
+
+ private final MongoCursor<Document> cursor;
+ private final Map<String, String> varToOriginalName;
+ private final BindingSet bindings;
+ private BindingSet nextSolution = null;
+
+ /**
+ * Constructor.
+ * @param aggIter Iterator of documents in
AggregationPipelineQueryNode's
+ * intermediate solution representation.
+ * @param varToOriginalName A mapping from field names in the pipeline
+ * result documents to equivalent variable names in the original
query.
+ * Where an entry does not exist for a field, the field name and
variable
+ * name are assumed to be the same.
+ * @param bindings A partial solution. May be empty.
+ */
+ public PipelineResultIteration(AggregateIterable<Document> aggIter,
+ Map<String, String> varToOriginalName,
+ BindingSet bindings) {
+ aggIter.batchSize(BATCH_SIZE);
+ this.cursor = aggIter.iterator();
+ this.varToOriginalName = varToOriginalName;
+ this.bindings = bindings;
+ lookahead();
+ }
+
+ private void lookahead() {
+ while (nextSolution == null && cursor.hasNext()) {
+ nextSolution = docToBindingSet(cursor.next());
+ }
+ }
+
+ @Override
+ public boolean hasNext() throws QueryEvaluationException {
+ lookahead();
+ return nextSolution != null;
+ }
+
+ @Override
+ public BindingSet next() throws QueryEvaluationException {
+ lookahead();
+ BindingSet solution = nextSolution;
+ nextSolution = null;
+ return solution;
+ }
+
+ @Override
+ public void remove() throws QueryEvaluationException {
+ lookahead();
+ nextSolution = null;
+ }
+
+ @Override
+ public void close() throws QueryEvaluationException {
+ cursor.close();
+ }
+
+ private QueryBindingSet docToBindingSet(Document result) {
+ QueryBindingSet bindingSet = new QueryBindingSet(bindings);
+ Document valueSet =
result.get(AggregationPipelineQueryNode.VALUES, Document.class);
+ Document typeSet = result.get(AggregationPipelineQueryNode.TYPES,
Document.class);
+ if (valueSet != null) {
+ for (Map.Entry<String, Object> entry : valueSet.entrySet()) {
+ String fieldName = entry.getKey();
+ String valueString = entry.getValue().toString();
+ String typeString = typeSet == null ? null :
typeSet.getString(fieldName);
+ String varName = varToOriginalName.getOrDefault(fieldName,
fieldName);
+ Value varValue;
+ if (typeString == null ||
typeString.equals(XMLSchema.ANYURI.stringValue())) {
+ varValue = VF.createURI(valueString);
+ }
+ else {
+ varValue = VF.createLiteral(valueString,
VF.createURI(typeString));
+ }
+ Binding existingBinding = bindingSet.getBinding(varName);
+ // If this variable is not already bound, add it.
+ if (existingBinding == null) {
+ bindingSet.addBinding(varName, varValue);
+ }
+ // If it's bound to something else, the solutions are
incompatible.
+ else if (!existingBinding.getValue().equals(varValue)) {
+ return null;
--- End diff --
This would cause your Iteration to periodically return null which will
likely result in a NPE by whoever is using it since that would be pretty
unexpected.
> Add the ability use the MongoDB aggregation pipeline to evaluate simple
> SPARQL expressions
> ------------------------------------------------------------------------------------------
>
> Key: RYA-416
> URL: https://issues.apache.org/jira/browse/RYA-416
> Project: Rya
> Issue Type: New Feature
> Reporter: Jesse Hatfield
> Assignee: Jesse Hatfield
>
> MongoDB provides the [aggregation pipeline
> framework|https://docs.mongodb.com/manual/core/aggregation-pipeline/] for
> multi-stage data processing. Currently, the query engine invokes this
> framework to apply individual statement patterns (using a "$match" expression
> for each and iterating through the results), then applies higher-level query
> operations (join, filter, select, project, etc) client-side.
> In principle, those high-level query operations could be rewritten as
> aggregation pipeline stages as well ($group, $match, $project, etc). This
> would allow more query evaluation logic to be executed by the MongoDB server
> itself, enabling server-side optimization. This could be used as a general
> query optimization, but would additionally be useful for any tool that only
> needed to write query results back to the server: adding a write step to the
> end of the resulting pipeline could obviate the need to communicate
> individual results to the client at all.
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