使用Neo4J OGM映射樹結構

Question

我正在使用Neo4J OGM（最新版本）將我的數據序列化為Neo4J嵌入式數據庫。

這適用於我的大多數實體，但是一旦我嘗試保存樹狀結構，它需要永遠保存並且似乎創建了數千個這樣的關系，雖然我只是保存一些節點：

RequestExecutor: 223 - creating new node id: -32715, 14690, [255, 100, 139, 207]
RequestExecutor: 223 - creating new node id: -32718, 14691, [29, 95]
RequestExecutor: 223 - creating new node id: -32721, 14692, [255, 102, 142, 212]
RequestExecutor: 223 - creating new node id: -32724, 14693, [30, 95]
RequestExecutor: 223 - creating new node id: -32727, 14694, [255, 103, 143, 213]
RequestExecutor: 223 - creating new node id: -32730, 14695, [31, 95]
RequestExecutor: 223 - creating new node id: -32733, 14696, [255, 103, 143, 213]
RequestExecutor: 223 - creating new node id: -32736, 14697, [32, 95]

這些展開操作也需要很長時間（此行更長，只是一個摘錄）：

EmbeddedRequest: 152 - Request: UNWIND {rows} as row MATCH (startNode) WHERE ID(startNode) = row.startNodeId WITH row,startNode MATCH (endNode) WHERE ID(endNode) = row.endNodeId MERGE (startNode)-[rel:`hasParentNd`]->(endNode) RETURN row.relRef as ref, ID(rel) as id, {type} as type with params {type=rel, rows=[{startNodeId=33, relRef=-32770, endNodeId=32, props={}}, {startNodeId=34, relRef=-32773, endNodeId=61, props={}}, {startNodeId=35, relRef=-32776, endNodeId=34, props={}}, {startNodeId=36, relRef=-32779, endNodeId=61, props={}}, {startNodeId=37, relRef=-32782, endNodeId=36, props={}}, {startNodeId=38, relRef=-32785, endNodeId=61, props={}}, {startNodeId=39, relRef=-19, endNodeId=14698, props={}}, {startNodeId=40, relRef=-32788, endNodeId=38, props={}}, {startNodeId=41, relRef=-22, endNodeId=39, props={}}, {startNodeId=42, relRef=-32791, endNodeId=61, props={}}, {startNodeId=43, relRef=-25, endNodeId=41,......

節點本身看起來像這樣。 NeoEntity類擁有唯一的ID。

@NodeEntity
public class NeoNode extends NeoEntity implements Node, Node.Op {

    @Property("unique")
    private boolean unique = true;

    @Relationship(type = "hasChildrenNd", direction = Relationship.INCOMING)
    private ArrayList<NeoNode.Op> children = new ArrayList<>();

    @Transient
    private NeoArtifact.Op<?> artifact;

    @Relationship(type = "hasParentNd")
    private Op parent;

    public NeoNode() {}
    ...
}

我嘗試過各種各樣的關系，但還沒有找到解決方案。 對任何想法都會非常感激。

---

附加信息：如果我讓它運行，它會填滿堆，直到它崩潰：

Exception in thread "neo4j.Scheduler-1" Exception in thread "Neo4j UDC Timer" java.lang.OutOfMemoryError: Java heap space

Answer 1

您不需要hasParentNd關系類型，因為所有neo4j關系都可以雙向導航。 您應該重新使用hasChildrenNd關系與相反的方向性。 這將允許雙向導航相同的關系實例（而不是創建新的冗余關系）。

嘗試將代碼更改為：

@NodeEntity 
public class NeoNode extends NeoEntity implements Node, Node.Op { 

    @Property("unique")
    private boolean unique = true;

    @Relationship(type = "hasChildrenNd", direction = Relationship.INCOMING)
    private ArrayList<Op> children = new ArrayList<>();

    @Transient 
    private NeoArtifact.Op<?> artifact; 

    @Relationship(type = "hasChildrenNd", direction = Relationship.OUTGOING)
    private Op parent;

    public NeoNode() {} 
    ... 
} 

旁白： hasChildrenNd類型名稱似乎令人困惑，因為傳出的hasChildrenNd關系指向父級而不是子級。