Join-Type implementation

Spring Data Elasticsearch 支持 Join data type以创建相应的索引映射并存储相关信息。

Setting up the data

实体用于父子连接关系中，它必须具有类型为 JoinField 的属性，该属性必须带有注释。我们假设一个 Statement 实体，其中语句可以是问题、答案、注释或投票（本例中还展示了一个 生成器，它不是必需的，但稍后在示例代码中使用）：

@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(Routing 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	有关路由相关的信息，请参阅 Routing values
2	一个问题可以有答案和评论
3	一个答案可以有投票
4	`JoinField` 属性用于把关系的名称 (question, answer, comment 或 vote) 和父 ID 结合在一起。普通类型必须和 `@Id` 注解的属性一样。

Spring Data Elasticsearch 将为此类生成以下映射：

{
  "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"
        }
      }
    }
  }
}

Storing data

给定此类的存储库，以下代码将插入一个问题、两个答案、一个注释和一个投票：

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());
}

1	create a question statement
2	该问题的第一答案
3	the second answer
4	该问题的评论
5	对第一个答案投赞成票，这需要将路由设置到 weather 文档，请参阅 Routing values。

Retrieving data

当前必须使用 native 查询来查询数据，因此不支持标准存储库方法。可以改用 repositories/custom-implementations.adoc。

以下代码展示了一个示例，说明如何使用 ElasticsearchOperations 实例来检索所有具有投票的条目（必须是答案，因为只有答案才可能获得投票）：

SearchHits<Statement> hasVotes() {

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

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