NgBatis ORM Framework for NebulaGraph

When using loops in NgBatis (specifically for Nebula v3.2.0+), you can access metadata about the current iteration by appending LP to the loop variable name. This allows you to reference the original parameter index or collection properties within the loop body.

If your loop variable is xxx, the available metadata properties are:

• xxxLP.index: Current index, starting from 1
• xxxLP.dataIndex: Current index, starting from 0
• xxxLP.size: Length of the collection
• xxxLP.first: Boolean, true if it is the first element
• xxxLP.last: Boolean, true if it is the last element
• xxxLP.even: Boolean, true if the index is even
• xxxLP.odd: Boolean, true if the index is odd

Example Usage for Parameter Passing: To pass the specific parameter variable name to the database during a loop, use the dataIndex property:

<insert id="insertPersonList">
    @for ( p in personList ) {
      INSERT VERTEX `person` ( name, gender )
        VALUES '${ p.name }' : ( '$personList[${pLP.dataIndex}].name', '$personList[${pLP.dataIndex}].gender' );
    @}
</insert>

NgBatis supports OGM, allowing you to execute queries directly from entity instances. To use this, your entities must extend specific base classes.

Vertex Entities

Extend GraphBaseVertex and use the @Tag annotation to specify the Tag name.

Edge Entities

Extend GraphBaseEdge and use the @EdgeType annotation. You can optionally use @Id, @SrcId, and @DstId to map properties to the edge's identity and connection points.

Querying

Once defined, you can call methods directly on the entity instance to perform lookups based on properties, tags, or topology.

@Tag(name = "player")
public class Player extends GraphBaseVertex {
  @Id
  private String id;
  private String name;
  private Integer age;
}

@EdgeType(name = "serve")
public class Serve extends GraphBaseEdge {
  @Id 
  private Long rank;
  @SrcId
  private String srcId;
  @DstId
  private String dstId;
  @Column(name = "start_year")
  private Integer startYear;
}

When a developer calls a method on a generated DAO interface (e.g., XXXDao), the following internal execution flow occurs:

1. Proxy Interception: The MapperProxy.invoke method intercepts the call, receiving the interface name, method name, and argument list.
2. Method Model Selection:
   • Standard Methods: The proxy directly invokes the method model with the provided arguments.
   • Pagination Methods: The proxy first retrieves and invokes the Count method model, followed by the Page method model.
3. Parameter & Template Resolution:
   • ArgsResolver converts the argument list into a Map type for easier access.
   • TextResolver performs template parameter replacement (mapping arguments to the query template).
4. Execution & Mapping:
   • The system executes the query via Session.executeWithParameter.
   • ResultResolver performs the ORM (Object-Relational Mapping) step, converting the raw result set into the data structure required by the method's return type.
5. Return: The processed result is returned to the caller as the expected type.

For Nebula Graph version 3.2.0 and above, you can pass parameter variable names directly to the database during data modification.

When using a loop, you can access a special helper object by appending LP to the loop variable name (e.g., if the loop is @for ( p in personList ), the helper is pLP). This allows you to reference the original collection and the specific index in the generated nGQL.

Available LP properties:

• xxxLP.index: Current index (starts from 1)
• xxxLP.dataIndex: Current index (starts from 0)
• xxxLP.size: Total size of the collection
• xxxLP.first: Boolean, true if it is the first element
• xxxLP.last: Boolean, true if it is the last element
• xxxLP.even: Boolean, true if the index is even
• xxxLP.odd: Boolean, true if the index is odd

<!-- PersonDao.xml for Nebula >= v3.2.0 -->
<insert id="insertPersonList">
    @for ( p in personList ) {
      INSERT VERTEX `person` ( name, gender )
        VALUES '${ p.name }' : ( '$personList[${pLP.dataIndex}].name', '$personList[${pLP.dataIndex}].gender' );
    @}
</insert>