连接类型实现

Doubao 中英对照 Join-Type implementation

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。

准备数据

要让一个实体用于父子连接关系，它必须有一个 JoinField 类型的属性，并且该属性必须加注解。假设我们有一个 Statement 实体，其中一条陈述可以是一个 question（问题）、一个 answer（回答）、一条 comment（评论）或一个 vote（投票）（本例中还展示了一个 Builder，它不是必需的，但后面的示例代码会用到）：

@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;
        }
    }
}

• 有关路由的相关信息，请参阅路由值

• 一个问题可以有回答和评论

• 一个回答可以有投票

• JoinField 属性用于将关系的名称（question、answer、comment 或 vote）与父 id 组合在一起。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

假设有了此类的仓库，以下代码插入一个问题、两个回答、一条评论和一个投票：

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());
}

• 创建一条问题陈述

• 该问题的第一个回答

• 第二个回答

• 对该问题的一条评论

• 对第一个回答的投票，这需要将路由设置为 weather 文档的路由，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，因此标准仓库方法不提供支持。可以改用自定义仓库实现。

以下代码作为示例，展示了如何使用 ElasticsearchOperations 实例检索所有具有 vote 的条目（这些条目必须是 answers，因为只有回答才能有投票）：

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);
}