一. ES parent-child 文档简介

ES 提供了类似数据库中 Join 联结的实现，可以通过 Join 类型的字段维护父子关系的数据，其父文档和子文档可以单独维护。

二. 父子文档的索引创建与数据插入

ES 父子文档的创建可以分为下面三步：

创建索引 Mapping，指明数据类型为 join 与父子文档名
插入父文档
插入子文档

下面针对每一步做演示。

1. 创建索引

假设我们有一个博客系统，每篇博客下有若干条评论，那么博客 blog 与评论 comment 就构成了一个父子关系。

父子文档的创建方为：

指定字段类型为 join
通过 relations 指定父子关系

示例如下：

# blog 为父文档，comment 为子文档
PUT blog_index
{"mappings": {"properties": {"blog_comment_join": {"type": "join","relations": {"blog": "comment"}}}}
}

2. 插入父文档

PUT blog_index/_doc/1
{"title": "First Blog","author": "Ahri","content": "This is my first blog","blog_comment_join": {"name": "blog"}
}PUT blog_index/_doc/2
{"title": "Second Blog","author": "EZ","content": "This is my second blog","blog_comment_join": "blog"
}

3. 插入子文档

插入子文档时需要注意一点：

routing 设置：子文档必须要与父文档存储在同一分片上，因此子文档的 routing 应该设置为父文档 ID 或者与父文档保持一致

示例代码如下：

PUT blog_index/_doc/comment-1?routing=1&refresh
{"user": "Tom","content": "Good blog","comment_date": "2020-01-01 10:00:00","blog_comment_join": {"name": "comment","parent": 1}
}PUT blog_index/_doc/comment-2?routing=1&refresh
{"user": "Jhon","content": "Good Job","comment_date": "2020-02-01 10:00:00","blog_comment_join": {"name": "comment","parent": 1}
}PUT blog_index/_doc/comment-3?routing=2&refresh
{"user": "Jack","content": "Great job","comment_date": "2020-01-01 10:00:00","blog_comment_join": {"name": "comment","parent": 2}
}

4. 其他

除了上面常见的父子文档类型，ES Join 还支持 多子文档 和 多级父子文档 的设置。如下：

构建多个子文档

Join 类型一个父文档可以配置多个子文档，创建方式如下：

PUT my_index
{"mappings": {"properties": {"my_join_field": {"type": "join","relations": {"question": ["answer", "comment"]  }}}}
}

构建多级父子关系

PUT my_index
{"mappings": {"properties": {"my_join_field": {"type": "join","relations": {"question": ["answer", "comment"],  "answer": "vote" }}}}
}

上面创建的父子文档层级如下图所示：

在这里插入图片描述

三. 父子文档的查询

基于父子文档的查询主要有三种：

parent_id：基于父文档 ID 查询所有的子文档
has_parent：查询符合条件的父文档的所有子文档
has_child：查询符合条件的子文档的所有父文档

下面是具体查询示例：

【1】parent_id 查询

# 查询 ID 为 1 父文档的所有子文档
GET blog_index_parent_child/_search
{"query": {"parent_id": {"type": "comment","id": 1}}
}# 结果返回
{"took" : 1,"timed_out" : false,"_shards" : {"total" : 1,"successful" : 1,"skipped" : 0,"failed" : 0},"hits" : {"total" : {"value" : 2,"relation" : "eq"},"max_score" : 0.44183275,"hits" : [{"_index" : "blog_index","_type" : "_doc","_id" : "comment-1","_score" : 0.44183275,"_routing" : "1","_source" : {"user" : "Tom","content" : "Good blog","comment_date" : "2020-01-01 10:00:00","blog_comment_join" : {"name" : "comment","parent" : 1}}},{"_index" : "blog_index","_type" : "_doc","_id" : "comment-2","_score" : 0.44183275,"_routing" : "1","_source" : {"user" : "Jhon","content" : "Good Job","comment_date" : "2020-02-01 10:00:00","blog_comment_join" : {"name" : "comment","parent" : 1}}}]}
}

【2】has_parent 查询

# 查询 title 包含 first 的父文档的所有子文档
GET blog_index/_search
{"query": {"has_parent": {"parent_type": "blog","query": {"match": {"title": "first"}}}}
}
# 结果返回
{"took" : 1,"timed_out" : false,"_shards" : {"total" : 1,"successful" : 1,"skipped" : 0,"failed" : 0},"hits" : {"total" : {"value" : 2,"relation" : "eq"},"max_score" : 1.0,"hits" : [{"_index" : "blog_index","_type" : "_doc","_id" : "comment-1","_score" : 1.0,"_routing" : "1","_source" : {"user" : "Tom","content" : "Good blog","comment_date" : "2020-01-01 10:00:00","blog_comment_join" : {"name" : "comment","parent" : 1}}},{"_index" : "blog_index","_type" : "_doc","_id" : "comment-2","_score" : 1.0,"_routing" : "1","_source" : {"user" : "Jhon","content" : "Good Job","comment_date" : "2020-02-01 10:00:00","blog_comment_join" : {"name" : "comment","parent" : 1}}}]}
}

【3】has_child 查询

# 查询 user 包含 Jack 的所有子文档的父文档
GET blog_index/_search
{"query": {"has_child": {"type": "comment","query": {"match": {"user": "Jack"}}}}
}
# 结果返回
{"took" : 1,"timed_out" : false,"_shards" : {"total" : 1,"successful" : 1,"skipped" : 0,"failed" : 0},"hits" : {"total" : {"value" : 1,"relation" : "eq"},"max_score" : 1.0,"hits" : [{"_index" : "blog_index","_type" : "_doc","_id" : "2","_score" : 1.0,"_source" : {"title" : "Second Blog","author" : "EZ","content" : "This is my second blog","blog_comment_join" : "blog"}}]}
}