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diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md index 6c57cd8b8e..e40f16e62d 100644 --- a/guides/source/active_record_querying.md +++ b/guides/source/active_record_querying.md @@ -1,4 +1,4 @@ -**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.** +**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON https://guides.rubyonrails.org.** Active Record Query Interface ============================= @@ -59,11 +59,13 @@ To retrieve objects from the database, Active Record provides several finder met The methods are: +* `annotate` * `find` * `create_with` * `distinct` * `eager_load` * `extending` +* `extract_associated` * `from` * `group` * `having` @@ -74,11 +76,13 @@ The methods are: * `lock` * `none` * `offset` +* `optimizer_hints` * `order` * `preload` * `readonly` * `references` * `reorder` +* `reselect` * `reverse_order` * `select` * `where` @@ -368,7 +372,7 @@ end **`:start`** -By default, records are fetched in ascending order of the primary key, which must be an integer. The `:start` option allows you to configure the first ID of the sequence whenever the lowest ID is not the one you need. This would be useful, for example, if you wanted to resume an interrupted batch process, provided you saved the last processed ID as a checkpoint. +By default, records are fetched in ascending order of the primary key. The `:start` option allows you to configure the first ID of the sequence whenever the lowest ID is not the one you need. This would be useful, for example, if you wanted to resume an interrupted batch process, provided you saved the last processed ID as a checkpoint. For example, to send newsletters only to users with the primary key starting from 2000: @@ -611,7 +615,8 @@ If you want to call `order` multiple times, subsequent orders will be appended t Client.order("orders_count ASC").order("created_at DESC") # SELECT * FROM clients ORDER BY orders_count ASC, created_at DESC ``` -WARNING: If you are using **MySQL 5.7.5** and above, then on selecting fields from a result set using methods like `select`, `pluck` and `ids`; the `order` method will raise an `ActiveRecord::StatementInvalid` exception unless the field(s) used in `order` clause are included in the select list. See the next section for selecting fields from the result set. + +WARNING: In most database systems, on selecting fields with `distinct` from a result set using methods like `select`, `pluck` and `ids`; the `order` method will raise an `ActiveRecord::StatementInvalid` exception unless the field(s) used in `order` clause are included in the select list. See the next section for selecting fields from the result set. Selecting Specific Fields ------------------------- @@ -623,6 +628,8 @@ To select only a subset of fields from the result set, you can specify the subse For example, to select only `viewable_by` and `locked` columns: ```ruby +Client.select(:viewable_by, :locked) +# OR Client.select("viewable_by, locked") ``` @@ -805,6 +812,32 @@ SELECT * FROM articles WHERE id > 10 ORDER BY id DESC LIMIT 20 ``` +### `reselect` + +The `reselect` method overrides an existing select statement. For example: + +```ruby +Post.select(:title, :body).reselect(:created_at) +``` + +The SQL that would be executed: + +```sql +SELECT `posts`.`created_at` FROM `posts` +``` + +In case the `reselect` clause is not used, + +```ruby +Post.select(:title, :body).select(:created_at) +``` + +the SQL executed would be: + +```sql +SELECT `posts`.`title`, `posts`.`body`, `posts`.`created_at` FROM `posts` +``` + ### `reorder` The `reorder` method overrides the default scope order. For example: @@ -1261,13 +1294,13 @@ articles, all the articles would still be loaded. By using `joins` (an INNER JOIN), the join conditions **must** match, otherwise no records will be returned. -NOTE: If an association is eager loaded as part of a join, any fields from a custom select clause will not present be on the loaded models. +NOTE: If an association is eager loaded as part of a join, any fields from a custom select clause will not be present on the loaded models. This is because it is ambiguous whether they should appear on the parent record, or the child. Scopes ------ -Scoping allows you to specify commonly-used queries which can be referenced as method calls on the association objects or models. With these scopes, you can use every method previously covered such as `where`, `joins` and `includes`. All scope methods will return an `ActiveRecord::Relation` object which will allow for further methods (such as other scopes) to be called on it. +Scoping allows you to specify commonly-used queries which can be referenced as method calls on the association objects or models. With these scopes, you can use every method previously covered such as `where`, `joins` and `includes`. All scope bodies should return an `ActiveRecord::Relation` or `nil` to allow for further methods (such as other scopes) to be called on it. To define a simple scope, we use the `scope` method inside the class, passing the query that we'd like to run when this scope is called: @@ -1277,16 +1310,6 @@ class Article < ApplicationRecord end ``` -This is exactly the same as defining a class method, and which you use is a matter of personal preference: - -```ruby -class Article < ApplicationRecord - def self.published - where(published: true) - end -end -``` - Scopes are also chainable within scopes: ```ruby @@ -1534,7 +1557,7 @@ book.available? # => false ``` Read the full documentation about enums -[in the Rails API docs](http://api.rubyonrails.org/classes/ActiveRecord/Enum.html). +[in the Rails API docs](https://api.rubyonrails.org/classes/ActiveRecord/Enum.html). Understanding The Method Chaining --------------------------------- @@ -1712,10 +1735,13 @@ Client.find_by_sql("SELECT * FROM clients ### `select_all` -`find_by_sql` has a close relative called `connection#select_all`. `select_all` will retrieve objects from the database using custom SQL just like `find_by_sql` but will not instantiate them. This method will return an instance of `ActiveRecord::Result` class and calling `to_hash` on this object would return you an array of hashes where each hash indicates a record. +`find_by_sql` has a close relative called `connection#select_all`. `select_all` will retrieve +objects from the database using custom SQL just like `find_by_sql` but will not instantiate them. +This method will return an instance of `ActiveRecord::Result` class and calling `to_a` on this +object would return you an array of hashes where each hash indicates a record. ```ruby -Client.connection.select_all("SELECT first_name, created_at FROM clients WHERE id = '1'").to_hash +Client.connection.select_all("SELECT first_name, created_at FROM clients WHERE id = '1'").to_a # => [ # {"first_name"=>"Rafael", "created_at"=>"2012-11-10 23:23:45.281189"}, # {"first_name"=>"Eileen", "created_at"=>"2013-12-09 11:22:35.221282"} @@ -2045,9 +2071,9 @@ under MySQL and MariaDB. Interpretation of the output of EXPLAIN is beyond the scope of this guide. The following pointers may be helpful: -* SQLite3: [EXPLAIN QUERY PLAN](http://www.sqlite.org/eqp.html) +* SQLite3: [EXPLAIN QUERY PLAN](https://www.sqlite.org/eqp.html) -* MySQL: [EXPLAIN Output Format](http://dev.mysql.com/doc/refman/5.7/en/explain-output.html) +* MySQL: [EXPLAIN Output Format](https://dev.mysql.com/doc/refman/5.7/en/explain-output.html) * MariaDB: [EXPLAIN](https://mariadb.com/kb/en/mariadb/explain/) |