> For the complete documentation index, see [llms.txt](https://kelby.gitbook.io/rails-beginner-s-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://kelby.gitbook.io/rails-beginner-s-guide/activerecord_db_opertion.md).

# Active Record 数据库操作：增删查改

Web 应用使用到数据库，而管理数据库使用的是 SQL 语言。我们不需要专门去学习 SQL，只需要用 Ruby 语言，写 Ruby 代码就能实现数据库的相关操作(也就是各种简单、复杂的读写操作)。

* Scoping

包括 Default、Named

* Relation

包括 Spawn Methods、Query Methods、Finder Methods、Calculations、Batches、~~Delegation~~、~~Predicate Builder~~、~~Merger~~

* Querying
* Persistence

即将被废除的 gem 'activerecord-deprecated\_finders'

* Counter Cache
* Attribute Assignment

主要工作由 ActiveModel::AttributeAssignment 完成，这里不再赘述。

* Attribute Methods

包括 Before Type Cast、Dirty、Primary Key、Query、Read & Write、Serialization、Time Zone Conversion

* ~~Null Relation~~
* ~~Dynamic Matchers~~


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