无法在orientdb中使用对象arraylist属性的arraylist保存对象

Question

我创建了一个数据库...

    ODatabaseObjectTx db = new ODatabaseObjectTx("memory:testt").create();
    db.getEntityManager().registerEntityClass(Vertex.class);
    db.getEntityManager().registerEntityClass(Edge.class);
    db.getEntityManager().registerEntityClass(ChemicalGraph.class);
    db.getEntityManager().registerEntityClass(Subgraph.class);

ChemicalGraph包含String，ArrayList<object>，ArrayList<Object>，并且在将其保存在db中时可以。但它对Subgraph不起作用。

ChemicalGraph类是......

这是子图类

import java.util.ArrayList;
public class Subgraph {

    public String gid = "";
    public int numV = 0;
    public int numE = 0;
    public ArrayList<ArrayList<Edge>> sgList = new ArrayList<ArrayList<Edge>>();


    public Subgraph()
    {

    }

    public Subgraph(ChemicalGraph g)
    {
        gid = g.gid;
        numV = g.vertices.size();
        numE = g.edges.size();
        sgList = g.decomposite();
    }

    public String toString()
    {
        StringBuilder sb = new StringBuilder();
        sb.append("Gid = ").append(gid).append(",  ");
        sb.append("NumV =").append(numV).append(",  ");
        sb.append("NumE=").append(numE).append(",  ");
        sb.append("SubgraphList=").append(sgList.toString()).append("  ");
        return sb.toString();
    }
}

我将其保存在数据库中

Subgraph s = new Subgraph(graph);
db.save(s);

我收到了以下错误

Exception in thread "main" java.lang.IllegalArgumentException: Type LINK must be a multi value type (collection or map)
    at com.orientechnologies.orient.core.serialization.serializer.object.OObjectSerializerHelper.multiValueToStream(OObjectSerializerHelper.java:752)
    at com.orientechnologies.orient.core.serialization.serializer.object.OObjectSerializerHelper.typeToStream(OObjectSerializerHelper.java:654)
    at com.orientechnologies.orient.core.serialization.serializer.object.OObjectSerializerHelper.multiValueToStream(OObjectSerializerHelper.java:763)
    at com.orientechnologies.orient.core.serialization.serializer.object.OObjectSerializerHelper.typeToStream(OObjectSerializerHelper.java:654)
    at com.orientechnologies.orient.core.serialization.serializer.object.OObjectSerializerHelper.toStream(OObjectSerializerHelper.java:577)
    at com.orientechnologies.orient.core.db.object.ODatabaseObjectTx.pojo2Stream(ODatabaseObjectTx.java:435)
    at com.orientechnologies.orient.core.db.object.ODatabaseObjectTx.save(ODatabaseObjectTx.java:226)
    at com.orientechnologies.orient.core.db.object.ODatabaseObjectTx.save(ODatabaseObjectTx.java:200)