Join-Type 实现

Spring Data Elasticsearch 支持 Join 数据类型，用于创建相应的索引映射并存储相关信息。

设置数据

为了在父子 Join 关系中使用实体，它必须具有类型为 JoinField 的属性，该属性必须被注解。假设有一个 Statement 实体，其中一个 statement 可能是一个*question*、一个*answer*、一个*comment*或一个*vote*（本示例中还展示了一个 *Builder*，这不是必需的，但稍后会在示例代码中使用）

@Document(indexName = "statements")
@Routing("routing")                                                                       (1)
public class Statement {
    @Id
    private String id;

    @Field(type = FieldType.Text)
    private String text;

    @Field(type = FieldType.Keyword)
    private String routing;

    @JoinTypeRelations(
        relations =
            {
                @JoinTypeRelation(parent = "question", children = {"answer", "comment"}), (2)
                @JoinTypeRelation(parent = "answer", children = "vote")                   (3)
            }
    )
    private JoinField<String> relation;                                                   (4)

    private Statement() {
    }

    public static StatementBuilder builder() {
        return new StatementBuilder();
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getRouting() {
        return routing;
    }

    public void setRouting(String routing) {
        this.routing = routing;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public JoinField<String> getRelation() {
        return relation;
    }

    public void setRelation(JoinField<String> relation) {
        this.relation = relation;
    }

    public static final class StatementBuilder {
        private String id;
        private String text;
        private String routing;
        private JoinField<String> relation;

        private StatementBuilder() {
        }

        public StatementBuilder withId(String id) {
            this.id = id;
            return this;
        }

        public StatementBuilder withRouting(String routing) {
            this.routing = routing;
            return this;
        }

        public StatementBuilder withText(String text) {
            this.text = text;
            return this;
        }

        public StatementBuilder withRelation(JoinField<String> relation) {
            this.relation = relation;
            return this;
        }

        public Statement build() {
            Statement statement = new Statement();
            statement.setId(id);
            statement.setRouting(routing);
            statement.setText(text);
            statement.setRelation(relation);
            return statement;
        }
    }
}

1	有关路由相关信息，请参阅路由值
2	一个 question 可以有 answer 和 comment
3	一个 answer 可以有 vote
4	`JoinField` 属性用于将关系的名称（question、answer、comment 或 vote）与父 ID 结合起来。泛型类型必须与 `@Id` 注解的属性相同。

Spring Data Elasticsearch 将为此类构建以下映射

{
  "statements": {
    "mappings": {
      "properties": {
        "_class": {
          "type": "text",
          "fields": {
            "keyword": {
              "type": "keyword",
              "ignore_above": 256
            }
          }
        },
        "routing": {
          "type": "keyword"
        },
        "relation": {
          "type": "join",
          "eager_global_ordinals": true,
          "relations": {
            "question": [
              "answer",
              "comment"
            ],
            "answer": "vote"
          }
        },
        "text": {
          "type": "text"
        }
      }
    }
  }
}

存储数据

给定此类的一个存储库，以下代码插入一个 question、两个 answer、一个 comment 和一个 vote

void init() {
    repository.deleteAll();

    Statement savedWeather = repository.save(
        Statement.builder()
            .withText("How is the weather?")
            .withRelation(new JoinField<>("question"))                          (1)
            .build());

    Statement sunnyAnswer = repository.save(
        Statement.builder()
            .withText("sunny")
            .withRelation(new JoinField<>("answer", savedWeather.getId()))      (2)
            .build());

    repository.save(
        Statement.builder()
            .withText("rainy")
            .withRelation(new JoinField<>("answer", savedWeather.getId()))      (3)
            .build());

    repository.save(
        Statement.builder()
            .withText("I don't like the rain")
            .withRelation(new JoinField<>("comment", savedWeather.getId()))     (4)
            .build());

    repository.save(
        Statement.builder()
            .withText("+1 for the sun")
            .withRouting(savedWeather.getId())
            .withRelation(new JoinField<>("vote", sunnyAnswer.getId()))         (5)
            .build());
}

1	创建一个 question statement
2	该 question 的第一个 answer
3	第二个 answer
4	question 的一个 comment
5	第一个 answer 的一个 vote，这需要将路由设置为 weather document，请参阅路由值。

检索数据

目前，必须使用原生查询来查询数据，因此标准存储库方法不支持。可以改用自定义存储库实现。

以下代码以示例的形式展示了如何使用 ElasticsearchOperations 实例检索所有具有 *vote* 的条目（必须是 *answer*，因为只有 answer 才能有 vote）

SearchHits<Statement> hasVotes() {

	Query query = NativeQuery.builder()
		.withQuery(co.elastic.clients.elasticsearch._types.query_dsl.Query.of(qb -> qb
			.hasChild(hc -> hc
				.type("answer")
				.queryName("vote")
				.query(matchAllQueryAsQuery())
				.scoreMode(ChildScoreMode.None)
			)))
		.build();

	return operations.search(query, Statement.class);
}