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Neo4j Based Recommendation Engine Module with real-time and pre-computed recommendations.
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/*
* Copyright (c) 2013-2020 GraphAware
*
* This file is part of the GraphAware Framework.
*
* GraphAware Framework is free software: you can redistribute it and/or modify it under the terms of
* the GNU General Public License as published by the Free Software Foundation, either
* version 3 of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
* without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
* See the GNU General Public License for more details. You should have received a copy of
* the GNU General Public License along with this program. If not, see
* "MATCH (p:Person)-[:FRIEND_OF]-(f)-[:FRIEND_OF]-(reco) WHERE NOT (p)-[:FRIEND_OF]-(reco) AND id(p)={id} RETURN reco, f.name as name, count(*) as score ORDER BY score DESC limit {limit}"
* {id} and {limit} will be provided as parameters by the engine. "reco" and "score" will become the recommended nodes
* and their respective scores. All other values returned by the query (e.g. "name" in this case) must be scalars and
* will become reasons for the recommendation.
*/
public abstract class BaseCypherEngine extends SingleScoreRecommendationEngine {
/**
* @return the Cypher query that returns recommendations. Can have {@link #idParamName()} as a placeholder
* representing the ID of the input node. Must return a set of nodes named {@link #recoResultName()}.
* Should return a score, i.e. a numerical value for each recommendation named {@link #scoreResultName()}.
* Can use {@link #limitParamName()} as a placeholder for Cypher LIMIT value. Must not be null or empty.
*/
protected abstract String query();
/**
* {@inheritDoc}
*/
@Override
protected final Map doRecommendSingle(Node input, Context context) {
Map result = new HashMap<>();
Result queryResult = input.getGraphDatabase().execute(query(), buildParams(input, context));
while (queryResult.hasNext()) {
Map row = queryResult.next();
addToResult(result, (Node) row.get(recoResultName()), buildScore(row));
}
return result;
}
/**
* Build parameters that will be passed into the Cypher query.
*
* @param input to the recommendation engine.
* @param context recommendation context.
* @return map of named parameters.
*/
protected Map buildParams(Node input, Context context) {
Map params = new HashMap<>();
params.put(idParamName(), input.getId());
params.put(limitParamName(), context.config().limit());
return params;
}
/**
* Build a score for a particular recommendation from a row of Cypher query results.
*
* @param row of results from Cypher query.
* @return score.
*/
protected PartialScore buildScore(Map row) {
if (row.containsKey(scoreResultName())) {
return new PartialScore(Float.valueOf(String.valueOf(row.get(scoreResultName()))), reasons(row));
}
return new PartialScore(defaultScore(), reasons(row));
}
/**
* Compute the reasons for a recommendation from all returned values, except {@link #scoreResultName()} and {@link #recoResultName()}.
*
* @param row of results from Cypher query.
* @return reasons. Cna be en empty map, but will never be null.
*/
protected Map reasons(Map row) {
Map result = new HashMap<>();
for (String key : row.keySet()) {
if (!key.equals(scoreResultName()) && !key.equals(recoResultName())) {
result.put(key, row.get(key));
}
}
return result;
}
/**
* Get the name of the parameter that represents input node ID.
*
* @return input node ID parameter name, "id" by default.
*/
protected String idParamName() {
return "id";
}
/**
* Get the name of the parameter that represents limit (to the number of results).
*
* @return limit parameter name, "limit" by default.
*/
protected String limitParamName() {
return "limit";
}
/**
* Get the name of the result column that contains computed recommendations.
*
* @return recommended items result name, "reco" by default.
*/
protected String recoResultName() {
return "reco";
}
/**
* Get the name of the result column that contains scores of computed recommendations.
*
* @return recommended items score result name, "score" by default.
*/
protected String scoreResultName() {
return "score";
}
/**
* Get default score value assigned to each recommendation in case the Cypher query result does not contain a score
* column.
*
* @return default score, 1.0 by default.
*/
protected float defaultScore() {
return 1;
}
/**
* {@inheritDoc}
*/
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
BaseCypherEngine that = (BaseCypherEngine) o;
if (!name().equals(that.name())) {
return false;
}
return query().equals(that.query());
}
/**
* {@inheritDoc}
*/
@Override
public int hashCode() {
int result = name().hashCode();
result = 31 * result + query().hashCode();
return result;
}
}