diff --git a/404_Parent_Child/40_Parent_child.asciidoc b/404_Parent_Child/40_Parent_child.asciidoc index 15b64a23e..87cc431f1 100644 --- a/404_Parent_Child/40_Parent_child.asciidoc +++ b/404_Parent_Child/40_Parent_child.asciidoc @@ -1,54 +1,26 @@ [[parent-child]] -== Parent-Child Relationship +== 父-子关系文档 -The _parent-child_ relationship is ((("relationships", "parent-child")))((("parent-child relationship")))similar in nature to the -<>: both allow you to associate one entity -with another. ((("nested objects", "parent-child relationships versus")))The difference is that, with nested objects, all entities live -within the same document while, with parent-child, the parent and children -are completely separate documents. +父-子关系文档 ((("relationships", "parent-child"))) ((("parent-child relationship"))) 在实质上类似于 <> ：允许将一个对象实体和另外一个对象实体关联起来。((("nested objects", "parent-child relationships versus")))而这两种类型的主要区别是：在 <> 文档中，所有对象都是在同一个文档中，而在父-子关系文档中，父对象和子对象都是完全独立的文档。 -The parent-child functionality allows you to associate one document type with -another, in a _one-to-many_ relationship--one parent to many children.((("one-to-many relationships"))) The -advantages that parent-child has over <> are as follows: +父-子关系的主要作用是允许把一个 type 的文档和另外一个 type 的文档关联起来，构成一对多的关系：一个父文档可以对应多个子文档 ((("one-to-many relationships"))) 。与 <> 相比，父-子关系的主要优势有： -* The parent document can be updated without reindexing the children. +* 更新父文档时，不会重新索引子文档。 +* 创建，修改或删除子文档时，不会影响父文档或其他子文档。这一点在这种场景下尤其有用：子文档数量较多，并且子文档创建和修改的频率高时。 +* 子文档可以作为搜索结果独立返回。 -* Child documents can be added, changed, or deleted without affecting either - the parent or other children. This is especially useful when child documents - are large in number and need to be added or changed frequently. - -* Child documents can be returned as the results of a search request. - -Elasticsearch maintains a map of which parents are associated with -which children. It is thanks to this map that query-time joins are fast, but -it does place a limitation on the parent-child relationship: _the parent -document and all of its children must live on the same shard_. - -The parent-child ID maps are stored in <>, which allows them to execute -quickly when fully hot in memory, but scalable enough to spill to disk when -the map is very large. +Elasticsearch 维护了一个父文档和子文档的映射关系，得益于这个映射，父-子文档关联查询操作非常快。但是这个映射也对父-子文档关系有个限制条件：父文档和其所有子文档，都必须要存储在同一个分片中。 +父-子文档ID映射存储在 <> 中。当映射完全在内存中时， <> 提供对映射的快速处理能力，另一方面当映射非常大时，可以通过溢出到磁盘提供足够的扩展能力 [[parent-child-mapping]] -=== Parent-Child Mapping +=== 父-子关系文档映射 -All that is needed in order to establish the parent-child relationship is to -specify which document type should be the parent of a child type.((("mapping (types)", "parent-child")))((("parent-child relationship", "parent-child mapping"))) This must -be done at index creation time, or with the `update-mapping` API before the -child type has been created. +建立父-子文档映射关系时只需要指定某一个文档 type 是另一个文档 type 的父亲。 ((("mapping (types)", "parent-child"))) ((("parent-child relationship", "parent-child mapping"))) 该关系可以在如下两个时间点设置：1）创建索引时；2）在子文档 type 创建之前更新父文档的 mapping。 -As an example, let's say that we have a company that has branches in many -cities. We would like to associate employees with the branch where they work. -We need to be able to search for branches, individual employees, and employees -who work for particular branches, so the nested model will not help. We -could, of course, -use <> or -<> here instead, but for demonstration -purposes we will use parent-child. +举例说明，有一个公司在多个城市有分公司，并且每一个分公司下面都有很多员工。有这样的需求：按照分公司、员工的维度去搜索，并且把员工和他们工作的分公司联系起来。针对该需求，用嵌套模型是无法实现的。当然，如果使用 <> 或者 <> 也是可以实现的，但是为了演示的目的，在这里我们使用父-子文档。 -All that we have to do is to tell Elasticsearch that the `employee` type has -the `branch` document type as its `_parent`, which we can do when we create -the index: +我们需要告诉Elasticsearch，在创建员工 `employee` 文档 type 时，指定分公司 `branch` 的文档 type 为其父亲。 [source,json] ------------------------- @@ -64,4 +36,4 @@ PUT /company } } ------------------------- -<1> Documents of type `employee` are children of type `branch`. +<1> `employee` 文档 是 `branch` 文档的子文档。