moshebla commented on a change in pull request #549: WIP:SOLR-13129 URL: https://github.com/apache/lucene-solr/pull/549#discussion_r254368025
########## File path: solr/solr-ref-guide/src/nested-documents.adoc ########## @@ -0,0 +1,321 @@ += Nested Child Documents +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +Solr supports indexing nested documents such as a blog post parent document and comments as child documents -- or products as parent documents and sizes, colors, or other variations as child documents. +The parent with all children is referred to as a "block" and it explains some of the nomenclature of related features. +At query time, the <<other-parsers.adoc#block-join-query-parsers,Block Join Query Parsers>> can search these relationships, + and the `<<transforming-result-documents.adoc#child-childdoctransformerfactory,[child]>>` Document Transformer can attach child documents to the result documents. +In terms of performance, indexing the relationships between documents usually yields much faster queries than an equivalent "query time join", + since the relationships are already stored in the index and do not need to be computed. +However, nested documents are less flexible than query time joins as it imposes rules that some applications may not be able to accept. + +.Note +[NOTE] +==== +A big limitation is that the whole block of parent-children documents must be updated or deleted together, not separately. +In other words, even if a single child document or the parent document is changed, the whole block of parent-child documents must be indexed together. +_Solr does not enforce this rule_; if it's violated, you may get sporadic query failures or incorrect results. +==== + +== Indexing Nested Documents + +Nested documents may be indexed via either the XML or JSON data syntax, and is also supported by <<using-solrj.adoc#using-solrj,SolrJ>> with javabin. + +=== Schema Configuration + +{nbsp} + +*Fields:* + + * The schema must include indexed field `\_root_`. The value of that field is populated automatically and is the same for all documents in the block, regardless of the inheritance depth. The id of the top document in every nested hierarchy is populated in this field. + + `<field name="\_root_" type="string" indexed="true" stored="false" docValues="false" />` + * `\_nest_path_` is used to store the path of the document in the hierarchy. This field is optional. + + `<fieldType name="\_nest_path_" class="solr.NestPathField" /> + <field name="\_nest_path_" type="_nest_path_" />` + * `\_nest_parent_` is used to store the `id` of the parent in the previous level. This field is optional. + + `<field name="\_nest_parent_" type="string" indexed="true" stored="true"/>` + * Nested documents are very much documents in their own right even if certain nested documents hold different information from the parent. + Therefore: + ** the schema must be able to represent the fields of any document + ** it may be infeasible to use `required` + ** even child documents need a unique `id` + * If you associate a child document as a field (e.g., comment), that field need not be defined in the schema, and probably + shouldn't be as it would be confusing. There is no child document field type. + +=== Rudimentary Root-only schemas + + * These schemas do not contain any other nested related fields apart from `\_root_`. + + In this mode relationship types(field names) between parents and their children are not saved. + + In this case <<nested-documents.adoc#child-doc-transformer,[child]>> transformer returns all children under the `\_childDocuments_` field. + * Typically you should have a field that differentiates a root doc from any nested children. However this isn't strictly necessary; so long as it's possible to write a query that can select only root documents somehow. Such a query is needed for the <<other-parsers.adoc#block-join-query-parsers,block join query parsers>> and <<nested-documents.adoc#child-doc-transformer,[child]>> doc transformer to function. + +=== XML Examples + +For example, here are two documents and their child documents. +It illustrates two styles of adding child documents; the first is associated via a field "comment" (preferred), +and the second is done in the classic way now referred to as an "anonymous" or "unlabelled" child document. +This field label relationship is available to the URP chain in Solr but is ultimately discarded. +Solr 8 will save the relationship. + +[source,xml] +---- +<add> + <doc> + <field name="id">1</field> + <field name="title">Solr adds block join support</field> + <field name="content_type">parentDocument</field> + <field name="content"> + <doc> + <field name="id">2</field> + <field name="comments">SolrCloud supports it too!</field> + </doc> + </field> + </doc> + <doc> + <field name="id">3</field> + <field name="title">New Lucene and Solr release is out</field> + <field name="content_type">parentDocument</field> + <doc> + <field name="id">4</field> + <field name="comments">Lots of new features</field> + </doc> + </doc> +</add> +---- + +In this example, we have indexed the parent documents with the field `content_type`, which has the value "parentDocument". +We could have also used a boolean field, such as `isParent`, with a value of "true", or any other similar approach. + +=== JSON Examples + +This example is equivalent to the XML example above. +Again, the field labelled relationship is preferred. +The labelled relationship here is one child document but could have been wrapped in array brackets. +For the anonymous relationship, note the special `\_childDocuments_` key whose contents must be an array of child documents. + +[source,json] +---- +[ + { + "id": "1", + "title": "Solr adds block join support", + "content_type": "parentDocument", + "comments": [{ + "id": "2", + "content": "SolrCloud supports it too!" + }, + { + "id": "3", + "content": "New filter syntax" + } + ] + }, + { + "id": "4", + "title": "New Lucene and Solr release is out", + "content_type": "parentDocument", + "_childDocuments_": [ + { + "id": "5", + "comments": "Lots of new features" + } + ] + } +] +---- + +.Root Only Mode +[NOTE] +==== + In Root-only schemas, these two documents will result in the same docs being indexed(Root-only schemas do not honor nested relationships). + When quried, child docs will be appended to _childDocuments_ key. Review comment: > Also, I think you meant to put backticks (``) around "_childDocuments_" - it's being converted into italics with only the underscores on either side. Seems fine both in site and PDF form. Guess this is OK since it is inside a note. I will fix the typo though, good catch. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org For additional commands, e-mail: dev-h...@lucene.apache.org
