BREAKING CHANGE(server): support "parent & child" EdgeLabel type (apa…

…che#2662)

HugeGraph supports the parent-child edge feature, meaning that an Edgelabel can have a subordinate type. Using the bank transfer graph as an example, transfers may include person-to-person transfers (person-to-person), person-to-company transfers (person-to-company), and company-to-company transfers (company-to-company). These three different types of transfers share a common operation, transfer.

In actual business scenarios, it is often necessary to retrieve all transfer edges with a single query. Currently, competitors can only manually split the transfer edge types, perform multiple queries, and then aggregate the results. With HugeGraph's parent-child edge feature, it is possible to query the corresponding person-to-person transfers, person-to-company transfers, and other sub-edge types, and also conveniently and efficiently retrieve all transfer-related edges at once.

PS: The parent-child edge feature for the cassandra and scylladb backends has been temporarily disabled through the store feature. 

> Code formatting will be done separately in the next PR.

Related to:
- apache#745
- apache#447

hugegraph-commons/hugegraph-common/src/main/java/org/apache/hugegraph/iterator/ExtendableIterator.java

@@ -21,6 +21,8 @@
 import java.util.Iterator;
 import java.util.concurrent.ConcurrentLinkedDeque;
 
+import com.google.common.base.Preconditions;
+
 import org.apache.hugegraph.util.E;
 
 public class ExtendableIterator<T> extends WrappedIterator<T> {
@@ -54,6 +56,15 @@ public ExtendableIterator<T> extend(Iterator<T> iter) {
         return this;
     }
 
+    public static <T> ExtendableIterator<T> concat(Iterator<T> lhs, Iterator<T> rhs) {
+        Preconditions.checkNotNull(lhs);
+        Preconditions.checkNotNull(rhs);
+        if (lhs instanceof ExtendableIterator) {
+            return ((ExtendableIterator<T>) lhs).extend(rhs);
+        }
+        return new ExtendableIterator<>(lhs, rhs);
+    }
+
     @Override
     public void close() throws Exception {
         for (Iterator<T> iter : this.itors) {

hugegraph-server/hugegraph-api/src/main/java/org/apache/hugegraph/api/graph/EdgeAPI.java

@@ -426,7 +426,15 @@ public static Direction parseDirection(String direction) {
 
     private Id getEdgeId(HugeGraph g, JsonEdge newEdge) {
         String sortKeys = "";
-        Id labelId = g.edgeLabel(newEdge.label).id();
+        EdgeLabel edgeLabel = g.edgeLabel(newEdge.label);
+        E.checkArgument(!edgeLabel.edgeLabelType().parent(),
+                        "The label of the created/updated edge is not allowed" +
+                        " to be the parent type");
+        Id labelId = edgeLabel.id();
+        Id subLabelId = edgeLabel.id();
+        if (edgeLabel.edgeLabelType().sub()) {
+            labelId = edgeLabel.fatherId();
+        }
         List<Id> sortKeyIds = g.edgeLabel(labelId).sortKeys();
         if (!sortKeyIds.isEmpty()) {
             List<Object> sortKeyValues = new ArrayList<>(sortKeyIds.size());
@@ -442,7 +450,7 @@ private Id getEdgeId(HugeGraph g, JsonEdge newEdge) {
             sortKeys = ConditionQuery.concatValues(sortKeyValues);
         }
         EdgeId edgeId = new EdgeId(HugeVertex.getIdValue(newEdge.source),
-                                   Directions.OUT, labelId, sortKeys,
+                                   Directions.OUT, labelId, subLabelId, sortKeys,
                                    HugeVertex.getIdValue(newEdge.target));
         if (newEdge.id != null) {
             E.checkArgument(edgeId.asString().equals(newEdge.id),

hugegraph-server/hugegraph-api/src/main/java/org/apache/hugegraph/api/schema/EdgeLabelAPI.java

@@ -21,6 +21,7 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 import org.apache.commons.collections.CollectionUtils;
 import org.apache.hugegraph.HugeGraph;
@@ -32,6 +33,7 @@
 import org.apache.hugegraph.define.Checkable;
 import org.apache.hugegraph.schema.EdgeLabel;
 import org.apache.hugegraph.schema.Userdata;
+import org.apache.hugegraph.type.define.EdgeLabelType;
 import org.apache.hugegraph.type.define.Frequency;
 import org.apache.hugegraph.type.define.GraphMode;
 import org.apache.hugegraph.util.E;
@@ -183,10 +185,16 @@ private static class JsonEdgeLabel implements Checkable {
         public long id;
         @JsonProperty("name")
         public String name;
+        @JsonProperty("edgelabel_type")
+        public EdgeLabelType edgeLabelType;
+        @JsonProperty("parent_label")
+        public String fatherLabel;
         @JsonProperty("source_label")
         public String sourceLabel;
         @JsonProperty("target_label")
         public String targetLabel;
+        @JsonProperty("links")
+        public Set<Map<String, String>> links;
         @JsonProperty("frequency")
         public Frequency frequency;
         @JsonProperty("properties")
@@ -223,12 +231,33 @@ private EdgeLabel.Builder convert2Builder(HugeGraph g) {
                                 g, g.mode());
                 builder.id(this.id);
             }
+            if (this.edgeLabelType == null) {
+                this.edgeLabelType = EdgeLabelType.NORMAL;
+            } else if (this.edgeLabelType.parent()) {
+                builder.asBase();
+            } else if (this.edgeLabelType.sub()) {
+                builder.withBase(this.fatherLabel);
+            } else {
+                E.checkArgument(this.edgeLabelType.normal(),
+                                "Please enter a valid edge_label_type value " +
+                                "in [NORMAL, PARENT, SUB]");
+            }
             if (this.sourceLabel != null) {
                 builder.sourceLabel(this.sourceLabel);
             }
             if (this.targetLabel != null) {
                 builder.targetLabel(this.targetLabel);
             }
+            if (this.links != null && !this.links.isEmpty()) {
+                for (Map<String, String> map : this.links) {
+                    E.checkArgument(map.size() == 1,
+                                    "The map size must be 1, due to it is a " +
+                                    "pair");
+                    Map.Entry<String, String> entry =
+                            map.entrySet().iterator().next();
+                    builder.link(entry.getKey(), entry.getValue());
+                }
+            }
             if (this.frequency != null) {
                 builder.frequency(this.frequency);
             }

hugegraph-server/hugegraph-cassandra/src/main/java/org/apache/hugegraph/backend/store/cassandra/CassandraFeatures.java

@@ -21,6 +21,11 @@
 
 public class CassandraFeatures implements BackendFeatures {
 
+    @Override
+    public boolean supportsFatherAndSubEdgeLabel() {
+        return false;
+    }
+
     @Override
     public boolean supportsScanToken() {
         return true;

hugegraph-server/hugegraph-cassandra/src/main/java/org/apache/hugegraph/backend/store/cassandra/CassandraTables.java

@@ -21,6 +21,8 @@
 import java.util.Arrays;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Objects;
+import java.util.stream.Collectors;
 
 import org.apache.hugegraph.backend.BackendException;
 import org.apache.hugegraph.backend.id.EdgeId;
@@ -51,6 +53,8 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 
+import org.apache.hugegraph.util.HashUtil;
+
 public class CassandraTables {
 
     public static final String LABEL_INDEX = "label_index";
@@ -400,7 +404,9 @@ protected List<HugeKeys> pkColumnName() {
 
         @Override
         protected List<HugeKeys> idColumnName() {
-            return Arrays.asList(EdgeId.KEYS);
+            return Arrays.stream(EdgeId.KEYS)
+                         .filter(key -> !Objects.equals(key, HugeKeys.SUB_LABEL))
+                         .collect(Collectors.toList());
         }
 
         @Override

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/HugeGraph.java

@@ -19,9 +19,12 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Set;
 
+import org.apache.commons.lang3.tuple.Pair;
 import org.apache.hugegraph.auth.AuthManager;
 import org.apache.hugegraph.backend.id.Id;
 import org.apache.hugegraph.backend.query.Query;
@@ -300,11 +303,25 @@ default Id[] mapElName2Id(String[] edgeLabels) {
         Id[] ids = new Id[edgeLabels.length];
         for (int i = 0; i < edgeLabels.length; i++) {
             EdgeLabel edgeLabel = this.edgeLabel(edgeLabels[i]);
-            ids[i] = edgeLabel.id();
+            if (edgeLabel.hasFather()) {
+                ids[i] = edgeLabel.fatherId();
+            } else {
+                ids[i] = edgeLabel.id();
+            }
         }
         return ids;
     }
 
+    default Set<Pair<String, String>> mapPairId2Name(
+            Set<Pair<Id, Id>> pairs) {
+        Set<Pair<String, String>> results = new HashSet<>(pairs.size());
+        for (Pair<Id, Id> pair : pairs) {
+            results.add(Pair.of(this.vertexLabel(pair.getLeft()).name(),
+                                this.vertexLabel(pair.getRight()).name()));
+        }
+        return results;
+    }
+
     default Id[] mapVlName2Id(String[] vertexLabels) {
         Id[] ids = new Id[vertexLabels.length];
         for (int i = 0; i < vertexLabels.length; i++) {
@@ -314,6 +331,14 @@ default Id[] mapVlName2Id(String[] vertexLabels) {
         return ids;
     }
 
+    default EdgeLabel[] mapElName2El(String[] edgeLabels) {
+        EdgeLabel[] els = new EdgeLabel[edgeLabels.length];
+        for (int i = 0; i < edgeLabels.length; i++) {
+            els[i] = this.edgeLabel(edgeLabels[i]);
+        }
+        return els;
+    }
+
     static void registerTraversalStrategies(Class<?> clazz) {
         TraversalStrategies strategies = TraversalStrategies.GlobalCache
                 .getStrategies(Graph.class)

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/cache/CachedBackendStore.java

@@ -18,8 +18,13 @@
 package org.apache.hugegraph.backend.cache;
 
 import java.util.Iterator;
+import java.util.List;
+import java.util.function.Function;
 
+import org.apache.hugegraph.HugeGraph;
 import org.apache.hugegraph.backend.id.Id;
+import org.apache.hugegraph.backend.query.ConditionQuery;
+import org.apache.hugegraph.backend.query.ConditionQueryFlatten;
 import org.apache.hugegraph.backend.query.Query;
 import org.apache.hugegraph.backend.store.BackendEntry;
 import org.apache.hugegraph.backend.store.BackendFeatures;
@@ -28,6 +33,8 @@
 import org.apache.hugegraph.backend.store.BackendStoreProvider;
 import org.apache.hugegraph.backend.store.SystemSchemaStore;
 import org.apache.hugegraph.config.HugeConfig;
+import org.apache.hugegraph.iterator.ExtendableIterator;
+import org.apache.hugegraph.iterator.MapperIterator;
 import org.apache.hugegraph.type.HugeType;
 import org.apache.hugegraph.util.StringEncoding;
 
@@ -177,6 +184,29 @@ public Iterator<BackendEntry> query(Query query) {
         }
     }
 
+    @Override
+    public Iterator<Iterator<BackendEntry>> query(Iterator<Query> queries,
+                                                  Function<Query, Query> queryWriter,
+                                                  HugeGraph hugeGraph) {
+        return new MapperIterator<>(queries, query -> {
+            assert query instanceof ConditionQuery;
+            List<ConditionQuery> flattenQueryList =
+                    ConditionQueryFlatten.flatten((ConditionQuery) query);
+
+            if (flattenQueryList.size() > 1) {
+                ExtendableIterator<BackendEntry> itExtend
+                        = new ExtendableIterator<>();
+                flattenQueryList.forEach(cq -> {
+                    Query cQuery = queryWriter.apply(cq);
+                    itExtend.extend(this.query(cQuery));
+                });
+                return itExtend;
+            } else {
+                return this.query(queryWriter.apply(query));
+            }
+        });
+    }
+
     @Override
     public Number queryNumber(Query query) {
         return this.store.queryNumber(query);