neo4j/src/main/java/org/apache/metamodel/neo4j/Neo4jDataContext.java - metamodel - Git at Google

 /**
  * 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.metamodel.neo4j;

 import java.util.ArrayList;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.stream.Collectors;

 import org.apache.http.HttpHost;
 import org.apache.http.client.methods.HttpGet;
 import org.apache.http.impl.client.CloseableHttpClient;
 import org.apache.http.impl.client.HttpClientBuilder;
 import org.apache.metamodel.DataContext;
 import org.apache.metamodel.MetaModelException;
 import org.apache.metamodel.QueryPostprocessDataContext;
 import org.apache.metamodel.data.DataSet;
 import org.apache.metamodel.data.DocumentSource;
 import org.apache.metamodel.query.FilterItem;
 import org.apache.metamodel.query.SelectItem;
 import org.apache.metamodel.schema.Column;
 import org.apache.metamodel.schema.MutableSchema;
 import org.apache.metamodel.schema.MutableTable;
 import org.apache.metamodel.schema.Schema;
 import org.apache.metamodel.schema.Table;
 import org.apache.metamodel.schema.builder.DocumentSourceProvider;
 import org.apache.metamodel.util.SimpleTableDef;
 import org.json.JSONArray;
 import org.json.JSONException;
 import org.json.JSONObject;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 /**
  * DataContext implementation for Neo4j
  */
 public class Neo4jDataContext extends QueryPostprocessDataContext implements DataContext, DocumentSourceProvider {

     public static final Logger logger = LoggerFactory.getLogger(Neo4jDataContext.class);

     public static final String SCHEMA_NAME = "neo4j";

     public static final int DEFAULT_PORT = 7474;

     public static final String RELATIONSHIP_PREFIX = "rel_";

     public static final String RELATIONSHIP_COLUMN_SEPARATOR = "#";

     private final SimpleTableDef[] _tableDefs;

     private final Neo4jRequestWrapper _requestWrapper;

     private final HttpHost _httpHost;

     private String _serviceRoot = "/db/data";

     public Neo4jDataContext(String hostname, int port, String username, String password, SimpleTableDef... tableDefs) {
         super(false);
         _httpHost = new HttpHost(hostname, port);
         final CloseableHttpClient httpClient = HttpClientBuilder.create().build();
         _requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, username, password, _serviceRoot);
         _tableDefs = tableDefs;
     }

     public Neo4jDataContext(String hostname, int port, String username, String password, String serviceRoot,
             SimpleTableDef... tableDefs) {
         super(false);
         _httpHost = new HttpHost(hostname, port);
         final CloseableHttpClient httpClient = HttpClientBuilder.create().build();
         _requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, username, password, _serviceRoot);
         _tableDefs = tableDefs;
         _serviceRoot = serviceRoot;
     }

     public Neo4jDataContext(String hostname, int port, String username, String password) {
         super(false);
         _httpHost = new HttpHost(hostname, port);
         final CloseableHttpClient httpClient = HttpClientBuilder.create().build();
         _requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, username, password, _serviceRoot);
         _tableDefs = detectTableDefs();
     }

     public Neo4jDataContext(String hostname, int port, String username, String password, String serviceRoot) {
         super(false);
         _httpHost = new HttpHost(hostname, port);
         final CloseableHttpClient httpClient = HttpClientBuilder.create().build();
         _requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, username, password, _serviceRoot);
         _tableDefs = detectTableDefs();
         _serviceRoot = serviceRoot;
     }

     public Neo4jDataContext(String hostname, int port, CloseableHttpClient httpClient) {
         super(false);
         _httpHost = new HttpHost(hostname, port);
         _requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, _serviceRoot);
         _tableDefs = detectTableDefs();
     }

     public Neo4jDataContext(String hostname, int port, CloseableHttpClient httpClient, String serviceRoot) {
         super(false);
         _httpHost = new HttpHost(hostname, port);
         _requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, _serviceRoot);
         _tableDefs = detectTableDefs();
         _serviceRoot = serviceRoot;
     }

     public Neo4jDataContext(String hostname, int port, CloseableHttpClient httpClient, SimpleTableDef... tableDefs) {
         super(false);
         _httpHost = new HttpHost(hostname, port);
         _requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, _serviceRoot);
         _tableDefs = tableDefs;
     }

     public Neo4jDataContext(String hostname, int port, CloseableHttpClient httpClient, String serviceRoot,
             SimpleTableDef... tableDefs) {
         super(false);
         _httpHost = new HttpHost(hostname, port);
         _requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, _serviceRoot);
         _tableDefs = tableDefs;
         _serviceRoot = serviceRoot;
     }

     @Override
     protected String getDefaultSchemaName() throws MetaModelException {
         return SCHEMA_NAME;
     }

     @Override
     protected Schema getMainSchema() throws MetaModelException {
         MutableSchema schema = new MutableSchema(getMainSchemaName());
         for (SimpleTableDef tableDef : _tableDefs) {
             MutableTable table = tableDef.toTable().setSchema(schema);
             schema.addTable(table);
         }
         return schema;
     }

     @Override
     protected String getMainSchemaName() throws MetaModelException {
         return SCHEMA_NAME;
     }

     public SimpleTableDef[] detectTableDefs() {
         List<SimpleTableDef> tableDefs = new ArrayList<SimpleTableDef>();

         String labelsJsonString = _requestWrapper.executeRestRequest(new HttpGet(_serviceRoot + "/labels"));

         JSONArray labelsJsonArray;
         try {
             labelsJsonArray = new JSONArray(labelsJsonString);
             for (int i = 0; i < labelsJsonArray.length(); i++) {
                 String label = labelsJsonArray.getString(i);

                 List<JSONObject> nodesPerLabel = getAllNodesPerLabel(label);

                 List<String> propertiesPerLabel = new ArrayList<String>();
                 for (JSONObject node : nodesPerLabel) {
                     List<String> propertiesPerNode = getAllPropertiesPerNode(node);
                     for (String property : propertiesPerNode) {
                         if (!propertiesPerLabel.contains(property)) {
                             propertiesPerLabel.add(property);
                         }
                     }
                 }

                 Set<String> relationshipPropertiesPerLabel = new LinkedHashSet<String>();
                 for (JSONObject node : nodesPerLabel) {
                     Integer nodeId = (Integer) node.getJSONObject("metadata").get("id");
                     List<JSONObject> relationshipsPerNode = getOutgoingRelationshipsPerNode(nodeId);
                     for (JSONObject relationship : relationshipsPerNode) {
                         // Add the relationship as a column in the table
                         String relationshipName = relationship.getString("type");
                         String relationshipNameProperty = RELATIONSHIP_PREFIX + relationshipName;
                         if (!relationshipPropertiesPerLabel.contains(relationshipNameProperty)) {
                             relationshipPropertiesPerLabel.add(relationshipNameProperty);
                         }

                         // Add all the relationship properties as table columns
                         List<String> propertiesPerRelationship = getAllPropertiesPerRelationship(relationship);
                         relationshipPropertiesPerLabel.addAll(propertiesPerRelationship);
                     }
                 }
                 propertiesPerLabel.addAll(relationshipPropertiesPerLabel);

                 // Do not add a table if label has no nodes (empty tables are
                 // considered non-existent)
                 if (!nodesPerLabel.isEmpty()) {
                     SimpleTableDef tableDef = new SimpleTableDef(label,
                             propertiesPerLabel.toArray(new String[propertiesPerLabel.size()]));
                     tableDefs.add(tableDef);
                 }
             }
             return tableDefs.toArray(new SimpleTableDef[tableDefs.size()]);
         } catch (JSONException e) {
             logger.error("Error occured in parsing JSON while detecting the schema: ", e);
             throw new IllegalStateException(e);
         }
     }

     private List<String> getAllPropertiesPerRelationship(JSONObject relationship) {
         List<String> propertyNames = new ArrayList<String>();
         try {
             String relationshipName = RELATIONSHIP_PREFIX + relationship.getJSONObject("metadata").getString("type");
             JSONObject relationshipPropertiesJSONObject = relationship.getJSONObject("data");
             if (relationshipPropertiesJSONObject.length() > 0) {
                 JSONArray relationshipPropertiesNamesJSONArray = relationshipPropertiesJSONObject.names();
                 for (int i = 0; i < relationshipPropertiesNamesJSONArray.length(); i++) {
                     String propertyName = relationshipName + RELATIONSHIP_COLUMN_SEPARATOR
                             + relationshipPropertiesNamesJSONArray.getString(i);
                     if (!propertyNames.contains(propertyName)) {
                         propertyNames.add(propertyName);
                     }
                 }
             }
             return propertyNames;
         } catch (JSONException e) {
             logger.error("Error occured in parsing JSON while getting relationship properties: ", e);
             throw new IllegalStateException(e);
         }
     }

     private List<JSONObject> getOutgoingRelationshipsPerNode(Integer nodeId) {
         List<JSONObject> outgoingRelationshipsPerNode = new ArrayList<JSONObject>();

         String outgoingRelationshipsPerNodeJsonString = _requestWrapper.executeRestRequest(new HttpGet(_serviceRoot
                 + "/node/" + nodeId + "/relationships/out"));

         JSONArray outgoingRelationshipsPerNodeJsonArray;
         try {
             outgoingRelationshipsPerNodeJsonArray = new JSONArray(outgoingRelationshipsPerNodeJsonString);
             for (int i = 0; i < outgoingRelationshipsPerNodeJsonArray.length(); i++) {
                 JSONObject relationship = outgoingRelationshipsPerNodeJsonArray.getJSONObject(i);
                 if (!outgoingRelationshipsPerNode.contains(relationship)) {
                     outgoingRelationshipsPerNode.add(relationship);
                 }
             }
             return outgoingRelationshipsPerNode;
         } catch (JSONException e) {
             logger.error("Error occured in parsing JSON while detecting outgoing relationships for node: " + nodeId, e);
             throw new IllegalStateException(e);
         }
     }

     private List<JSONObject> getAllNodesPerLabel(String label) {
         List<JSONObject> allNodesPerLabel = new ArrayList<JSONObject>();

         String allNodesForLabelJsonString = _requestWrapper.executeRestRequest(new HttpGet(_serviceRoot + "/label/"
                 + label + "/nodes"));

         JSONArray allNodesForLabelJsonArray;
         try {
             allNodesForLabelJsonArray = new JSONArray(allNodesForLabelJsonString);
             for (int i = 0; i < allNodesForLabelJsonArray.length(); i++) {
                 JSONObject node = allNodesForLabelJsonArray.getJSONObject(i);
                 allNodesPerLabel.add(node);
             }
             return allNodesPerLabel;
         } catch (JSONException e) {
             logger.error("Error occured in parsing JSON while detecting the nodes for a label: " + label, e);
             throw new IllegalStateException(e);
         }
     }

     private List<String> getAllPropertiesPerNode(JSONObject node) {
         List<String> properties = new ArrayList<String>();
         properties.add("_id");

         String propertiesEndpoint;
         try {
             propertiesEndpoint = node.getString("properties");

             String allPropertiesPerNodeJsonString = _requestWrapper.executeRestRequest(new HttpGet(propertiesEndpoint));

             JSONObject allPropertiesPerNodeJsonObject = new JSONObject(allPropertiesPerNodeJsonString);
             for (int j = 0; j < allPropertiesPerNodeJsonObject.length(); j++) {
                 JSONArray propertiesJsonArray = allPropertiesPerNodeJsonObject.names();
                 for (int k = 0; k < propertiesJsonArray.length(); k++) {
                     String property = propertiesJsonArray.getString(k);
                     properties.add(property);
                 }
             }
             return properties;
         } catch (JSONException e) {
             logger.error("Error occured in parsing JSON while detecting the properties of a node: " + node, e);
             throw new IllegalStateException(e);
         }
     }

     @Override
     protected DataSet materializeMainSchemaTable(Table table, List<Column> columns, int firstRow, int maxRows) {
         if ((columns != null) && (columns.size() > 0)) {
             Neo4jDataSet dataSet = null;
             try {
                 String selectQuery = Neo4jCypherQueryBuilder.buildSelectQuery(table, columns, firstRow, maxRows);
                 String responseJSONString = _requestWrapper.executeCypherQuery(selectQuery);
                 JSONObject resultJSONObject = new JSONObject(responseJSONString);
                 final List<SelectItem> selectItems = columns.stream().map(SelectItem::new).collect(Collectors.toList());
                 dataSet = new Neo4jDataSet(selectItems, resultJSONObject);
             } catch (JSONException e) {
                 logger.error("Error occured in parsing JSON while materializing the schema: ", e);
                 throw new IllegalStateException(e);
             }

             return dataSet;
         } else {
             logger.error("Encountered null or empty columns array for materializing main schema table.");
             throw new IllegalArgumentException("Columns cannot be null or empty array");
         }
     }

     @Override
     protected DataSet materializeMainSchemaTable(Table table, List<Column> columns, int maxRows) {
         return materializeMainSchemaTable(table, columns, 1, maxRows);
     }

     @Override
     protected Number executeCountQuery(Table table, List<FilterItem> whereItems, boolean functionApproximationAllowed) {
         String countQuery = Neo4jCypherQueryBuilder.buildCountQuery(table.getName(), whereItems);
         String jsonResponse = _requestWrapper.executeCypherQuery(countQuery);

         JSONObject jsonResponseObject;
         try {
             jsonResponseObject = new JSONObject(jsonResponse);
             JSONArray resultsJSONArray = jsonResponseObject.getJSONArray("results");
             JSONObject resultJSONObject = (JSONObject) resultsJSONArray.get(0);
             JSONArray dataJSONArray = resultJSONObject.getJSONArray("data");
             JSONObject rowJSONObject = (JSONObject) dataJSONArray.get(0);
             JSONArray valueJSONArray = rowJSONObject.getJSONArray("row");
             Number value = (Number) valueJSONArray.get(0);
             return value;
         } catch (JSONException e) {
             logger.error("Error occured in parsing JSON response: ", e);
             // Do not throw an exception here. Returning null here will make
             // MetaModel attempt to count records manually and therefore recover
             // from the error.
             return null;
         }
     }

     @Override
     public DocumentSource getMixedDocumentSourceForSampling() {
         return null;
     }

     @Override
     public DocumentSource getDocumentSourceForTable(String sourceCollectionName) {
         return null;
     }
 }
	/**
	* 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.metamodel.neo4j;

	import java.util.ArrayList;
	import java.util.LinkedHashSet;
	import java.util.List;
	import java.util.Set;
	import java.util.stream.Collectors;

	import org.apache.http.HttpHost;
	import org.apache.http.client.methods.HttpGet;
	import org.apache.http.impl.client.CloseableHttpClient;
	import org.apache.http.impl.client.HttpClientBuilder;
	import org.apache.metamodel.DataContext;
	import org.apache.metamodel.MetaModelException;
	import org.apache.metamodel.QueryPostprocessDataContext;
	import org.apache.metamodel.data.DataSet;
	import org.apache.metamodel.data.DocumentSource;
	import org.apache.metamodel.query.FilterItem;
	import org.apache.metamodel.query.SelectItem;
	import org.apache.metamodel.schema.Column;
	import org.apache.metamodel.schema.MutableSchema;
	import org.apache.metamodel.schema.MutableTable;
	import org.apache.metamodel.schema.Schema;
	import org.apache.metamodel.schema.Table;
	import org.apache.metamodel.schema.builder.DocumentSourceProvider;
	import org.apache.metamodel.util.SimpleTableDef;
	import org.json.JSONArray;
	import org.json.JSONException;
	import org.json.JSONObject;
	import org.slf4j.Logger;
	import org.slf4j.LoggerFactory;

	/**
	* DataContext implementation for Neo4j
	*/
	public class Neo4jDataContext extends QueryPostprocessDataContext implements DataContext, DocumentSourceProvider {

	public static final Logger logger = LoggerFactory.getLogger(Neo4jDataContext.class);

	public static final String SCHEMA_NAME = "neo4j";

	public static final int DEFAULT_PORT = 7474;

	public static final String RELATIONSHIP_PREFIX = "rel_";

	public static final String RELATIONSHIP_COLUMN_SEPARATOR = "#";

	private final SimpleTableDef[] _tableDefs;

	private final Neo4jRequestWrapper _requestWrapper;

	private final HttpHost _httpHost;

	private String _serviceRoot = "/db/data";

	public Neo4jDataContext(String hostname, int port, String username, String password, SimpleTableDef... tableDefs) {
	super(false);
	_httpHost = new HttpHost(hostname, port);
	final CloseableHttpClient httpClient = HttpClientBuilder.create().build();
	_requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, username, password, _serviceRoot);
	_tableDefs = tableDefs;
	}

	public Neo4jDataContext(String hostname, int port, String username, String password, String serviceRoot,
	SimpleTableDef... tableDefs) {
	super(false);
	_httpHost = new HttpHost(hostname, port);
	final CloseableHttpClient httpClient = HttpClientBuilder.create().build();
	_requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, username, password, _serviceRoot);
	_tableDefs = tableDefs;
	_serviceRoot = serviceRoot;
	}

	public Neo4jDataContext(String hostname, int port, String username, String password) {
	super(false);
	_httpHost = new HttpHost(hostname, port);
	final CloseableHttpClient httpClient = HttpClientBuilder.create().build();
	_requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, username, password, _serviceRoot);
	_tableDefs = detectTableDefs();
	}

	public Neo4jDataContext(String hostname, int port, String username, String password, String serviceRoot) {
	super(false);
	_httpHost = new HttpHost(hostname, port);
	final CloseableHttpClient httpClient = HttpClientBuilder.create().build();
	_requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, username, password, _serviceRoot);
	_tableDefs = detectTableDefs();
	_serviceRoot = serviceRoot;
	}

	public Neo4jDataContext(String hostname, int port, CloseableHttpClient httpClient) {
	super(false);
	_httpHost = new HttpHost(hostname, port);
	_requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, _serviceRoot);
	_tableDefs = detectTableDefs();
	}

	public Neo4jDataContext(String hostname, int port, CloseableHttpClient httpClient, String serviceRoot) {
	super(false);
	_httpHost = new HttpHost(hostname, port);
	_requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, _serviceRoot);
	_tableDefs = detectTableDefs();
	_serviceRoot = serviceRoot;
	}

	public Neo4jDataContext(String hostname, int port, CloseableHttpClient httpClient, SimpleTableDef... tableDefs) {
	super(false);
	_httpHost = new HttpHost(hostname, port);
	_requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, _serviceRoot);
	_tableDefs = tableDefs;
	}

	public Neo4jDataContext(String hostname, int port, CloseableHttpClient httpClient, String serviceRoot,
	SimpleTableDef... tableDefs) {
	super(false);
	_httpHost = new HttpHost(hostname, port);
	_requestWrapper = new Neo4jRequestWrapper(httpClient, _httpHost, _serviceRoot);
	_tableDefs = tableDefs;
	_serviceRoot = serviceRoot;
	}

	@Override
	protected String getDefaultSchemaName() throws MetaModelException {
	return SCHEMA_NAME;
	}

	@Override
	protected Schema getMainSchema() throws MetaModelException {
	MutableSchema schema = new MutableSchema(getMainSchemaName());
	for (SimpleTableDef tableDef : _tableDefs) {
	MutableTable table = tableDef.toTable().setSchema(schema);
	schema.addTable(table);
	}
	return schema;
	}

	@Override
	protected String getMainSchemaName() throws MetaModelException {
	return SCHEMA_NAME;
	}

	public SimpleTableDef[] detectTableDefs() {
	List<SimpleTableDef> tableDefs = new ArrayList<SimpleTableDef>();

	String labelsJsonString = _requestWrapper.executeRestRequest(new HttpGet(_serviceRoot + "/labels"));

	JSONArray labelsJsonArray;
	try {
	labelsJsonArray = new JSONArray(labelsJsonString);
	for (int i = 0; i < labelsJsonArray.length(); i++) {
	String label = labelsJsonArray.getString(i);

	List<JSONObject> nodesPerLabel = getAllNodesPerLabel(label);

	List<String> propertiesPerLabel = new ArrayList<String>();
	for (JSONObject node : nodesPerLabel) {
	List<String> propertiesPerNode = getAllPropertiesPerNode(node);
	for (String property : propertiesPerNode) {
	if (!propertiesPerLabel.contains(property)) {
	propertiesPerLabel.add(property);
	}
	}
	}

	Set<String> relationshipPropertiesPerLabel = new LinkedHashSet<String>();
	for (JSONObject node : nodesPerLabel) {
	Integer nodeId = (Integer) node.getJSONObject("metadata").get("id");
	List<JSONObject> relationshipsPerNode = getOutgoingRelationshipsPerNode(nodeId);
	for (JSONObject relationship : relationshipsPerNode) {
	// Add the relationship as a column in the table
	String relationshipName = relationship.getString("type");
	String relationshipNameProperty = RELATIONSHIP_PREFIX + relationshipName;
	if (!relationshipPropertiesPerLabel.contains(relationshipNameProperty)) {
	relationshipPropertiesPerLabel.add(relationshipNameProperty);
	}

	// Add all the relationship properties as table columns
	List<String> propertiesPerRelationship = getAllPropertiesPerRelationship(relationship);
	relationshipPropertiesPerLabel.addAll(propertiesPerRelationship);
	}
	}
	propertiesPerLabel.addAll(relationshipPropertiesPerLabel);

	// Do not add a table if label has no nodes (empty tables are
	// considered non-existent)
	if (!nodesPerLabel.isEmpty()) {
	SimpleTableDef tableDef = new SimpleTableDef(label,
	propertiesPerLabel.toArray(new String[propertiesPerLabel.size()]));
	tableDefs.add(tableDef);
	}
	}
	return tableDefs.toArray(new SimpleTableDef[tableDefs.size()]);
	} catch (JSONException e) {
	logger.error("Error occured in parsing JSON while detecting the schema: ", e);
	throw new IllegalStateException(e);
	}
	}

	private List<String> getAllPropertiesPerRelationship(JSONObject relationship) {
	List<String> propertyNames = new ArrayList<String>();
	try {
	String relationshipName = RELATIONSHIP_PREFIX + relationship.getJSONObject("metadata").getString("type");
	JSONObject relationshipPropertiesJSONObject = relationship.getJSONObject("data");
	if (relationshipPropertiesJSONObject.length() > 0) {
	JSONArray relationshipPropertiesNamesJSONArray = relationshipPropertiesJSONObject.names();
	for (int i = 0; i < relationshipPropertiesNamesJSONArray.length(); i++) {
	String propertyName = relationshipName + RELATIONSHIP_COLUMN_SEPARATOR
	+ relationshipPropertiesNamesJSONArray.getString(i);
	if (!propertyNames.contains(propertyName)) {
	propertyNames.add(propertyName);
	}
	}
	}
	return propertyNames;
	} catch (JSONException e) {
	logger.error("Error occured in parsing JSON while getting relationship properties: ", e);
	throw new IllegalStateException(e);
	}
	}

	private List<JSONObject> getOutgoingRelationshipsPerNode(Integer nodeId) {
	List<JSONObject> outgoingRelationshipsPerNode = new ArrayList<JSONObject>();

	String outgoingRelationshipsPerNodeJsonString = _requestWrapper.executeRestRequest(new HttpGet(_serviceRoot
	+ "/node/" + nodeId + "/relationships/out"));

	JSONArray outgoingRelationshipsPerNodeJsonArray;
	try {
	outgoingRelationshipsPerNodeJsonArray = new JSONArray(outgoingRelationshipsPerNodeJsonString);
	for (int i = 0; i < outgoingRelationshipsPerNodeJsonArray.length(); i++) {
	JSONObject relationship = outgoingRelationshipsPerNodeJsonArray.getJSONObject(i);
	if (!outgoingRelationshipsPerNode.contains(relationship)) {
	outgoingRelationshipsPerNode.add(relationship);
	}
	}
	return outgoingRelationshipsPerNode;
	} catch (JSONException e) {
	logger.error("Error occured in parsing JSON while detecting outgoing relationships for node: " + nodeId, e);
	throw new IllegalStateException(e);
	}
	}

	private List<JSONObject> getAllNodesPerLabel(String label) {
	List<JSONObject> allNodesPerLabel = new ArrayList<JSONObject>();

	String allNodesForLabelJsonString = _requestWrapper.executeRestRequest(new HttpGet(_serviceRoot + "/label/"
	+ label + "/nodes"));

	JSONArray allNodesForLabelJsonArray;
	try {
	allNodesForLabelJsonArray = new JSONArray(allNodesForLabelJsonString);
	for (int i = 0; i < allNodesForLabelJsonArray.length(); i++) {
	JSONObject node = allNodesForLabelJsonArray.getJSONObject(i);
	allNodesPerLabel.add(node);
	}
	return allNodesPerLabel;
	} catch (JSONException e) {
	logger.error("Error occured in parsing JSON while detecting the nodes for a label: " + label, e);
	throw new IllegalStateException(e);
	}
	}

	private List<String> getAllPropertiesPerNode(JSONObject node) {
	List<String> properties = new ArrayList<String>();
	properties.add("_id");

	String propertiesEndpoint;
	try {
	propertiesEndpoint = node.getString("properties");

	String allPropertiesPerNodeJsonString = _requestWrapper.executeRestRequest(new HttpGet(propertiesEndpoint));

	JSONObject allPropertiesPerNodeJsonObject = new JSONObject(allPropertiesPerNodeJsonString);
	for (int j = 0; j < allPropertiesPerNodeJsonObject.length(); j++) {
	JSONArray propertiesJsonArray = allPropertiesPerNodeJsonObject.names();
	for (int k = 0; k < propertiesJsonArray.length(); k++) {
	String property = propertiesJsonArray.getString(k);
	properties.add(property);
	}
	}
	return properties;
	} catch (JSONException e) {
	logger.error("Error occured in parsing JSON while detecting the properties of a node: " + node, e);
	throw new IllegalStateException(e);
	}
	}

	@Override
	protected DataSet materializeMainSchemaTable(Table table, List<Column> columns, int firstRow, int maxRows) {
	if ((columns != null) && (columns.size() > 0)) {
	Neo4jDataSet dataSet = null;
	try {
	String selectQuery = Neo4jCypherQueryBuilder.buildSelectQuery(table, columns, firstRow, maxRows);
	String responseJSONString = _requestWrapper.executeCypherQuery(selectQuery);
	JSONObject resultJSONObject = new JSONObject(responseJSONString);
	final List<SelectItem> selectItems = columns.stream().map(SelectItem::new).collect(Collectors.toList());
	dataSet = new Neo4jDataSet(selectItems, resultJSONObject);
	} catch (JSONException e) {
	logger.error("Error occured in parsing JSON while materializing the schema: ", e);
	throw new IllegalStateException(e);
	}

	return dataSet;
	} else {
	logger.error("Encountered null or empty columns array for materializing main schema table.");
	throw new IllegalArgumentException("Columns cannot be null or empty array");
	}
	}

	@Override
	protected DataSet materializeMainSchemaTable(Table table, List<Column> columns, int maxRows) {
	return materializeMainSchemaTable(table, columns, 1, maxRows);
	}

	@Override
	protected Number executeCountQuery(Table table, List<FilterItem> whereItems, boolean functionApproximationAllowed) {
	String countQuery = Neo4jCypherQueryBuilder.buildCountQuery(table.getName(), whereItems);
	String jsonResponse = _requestWrapper.executeCypherQuery(countQuery);

	JSONObject jsonResponseObject;
	try {
	jsonResponseObject = new JSONObject(jsonResponse);
	JSONArray resultsJSONArray = jsonResponseObject.getJSONArray("results");
	JSONObject resultJSONObject = (JSONObject) resultsJSONArray.get(0);
	JSONArray dataJSONArray = resultJSONObject.getJSONArray("data");
	JSONObject rowJSONObject = (JSONObject) dataJSONArray.get(0);
	JSONArray valueJSONArray = rowJSONObject.getJSONArray("row");
	Number value = (Number) valueJSONArray.get(0);
	return value;
	} catch (JSONException e) {
	logger.error("Error occured in parsing JSON response: ", e);
	// Do not throw an exception here. Returning null here will make
	// MetaModel attempt to count records manually and therefore recover
	// from the error.
	return null;
	}
	}

	@Override
	public DocumentSource getMixedDocumentSourceForSampling() {
	return null;
	}

	@Override
	public DocumentSource getDocumentSourceForTable(String sourceCollectionName) {
	return null;
	}
	}