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Diffstat (limited to 'guides/source/active_record_querying.md')
| -rw-r--r-- | guides/source/active_record_querying.md | 53 |
1 files changed, 32 insertions, 21 deletions
diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md index 26d01d4ede..4e28e31a53 100644 --- a/guides/source/active_record_querying.md +++ b/guides/source/active_record_querying.md @@ -118,7 +118,7 @@ You can also use this method to query for multiple objects. Call the `find` meth ```ruby # Find the clients with primary keys 1 and 10. -client = Client.find([1, 10]) # Or even Client.find(1, 10) +clients = Client.find([1, 10]) # Or even Client.find(1, 10) # => [#<Client id: 1, first_name: "Lifo">, #<Client id: 10, first_name: "Ryan">] ``` @@ -150,7 +150,7 @@ The `take` method returns `nil` if no record is found and no exception will be r You can pass in a numerical argument to the `take` method to return up to that number of results. For example ```ruby -client = Client.take(2) +clients = Client.take(2) # => [ # #<Client id: 1, first_name: "Lifo">, # #<Client id: 220, first_name: "Sara"> @@ -189,7 +189,7 @@ If your [default scope](active_record_querying.html#applying-a-default-scope) co You can pass in a numerical argument to the `first` method to return up to that number of results. For example ```ruby -client = Client.first(3) +clients = Client.first(3) # => [ # #<Client id: 1, first_name: "Lifo">, # #<Client id: 2, first_name: "Fifo">, @@ -240,7 +240,7 @@ If your [default scope](active_record_querying.html#applying-a-default-scope) co You can pass in a numerical argument to the `last` method to return up to that number of results. For example ```ruby -client = Client.last(3) +clients = Client.last(3) # => [ # #<Client id: 219, first_name: "James">, # #<Client id: 220, first_name: "Sara">, @@ -414,7 +414,7 @@ end `find_in_batches` works on model classes, as seen above, and also on relations: ```ruby -Invoice.pending.find_in_batches do |invoice| +Invoice.pending.find_in_batches do |invoices| pending_invoices_export.add_invoices(invoices) end ``` @@ -513,8 +513,6 @@ Article.where(author: author) Author.joins(:articles).where(articles: { author: author }) ``` -NOTE: The values cannot be symbols. For example, you cannot do `Client.where(status: :active)`. - #### Range Conditions ```ruby @@ -557,6 +555,19 @@ In other words, this query can be generated by calling `where` with no argument, SELECT * FROM clients WHERE (clients.locked != 1) ``` +### OR Conditions + +`OR` conditions between two relations can be built by calling `or` on the first +relation, and passing the second one as an argument. + +```ruby +Client.where(locked: true).or(Client.where(orders_count: [1,3,5])) +``` + +```sql +SELECT * FROM clients WHERE (clients.locked = 1 OR clients.orders_count IN (1,3,5)) +``` + Ordering -------- @@ -790,7 +801,7 @@ The SQL that would be executed: SELECT * FROM articles WHERE id > 10 ORDER BY id DESC # Original query without `only` -SELECT "articles".* FROM "articles" WHERE (id > 10) ORDER BY id desc LIMIT 20 +SELECT * FROM articles WHERE id > 10 ORDER BY id DESC LIMIT 20 ``` @@ -809,14 +820,14 @@ Article.find(10).comments.reorder('name') The SQL that would be executed: ```sql -SELECT * FROM articles WHERE id = 10 +SELECT * FROM articles WHERE id = 10 LIMIT 1 SELECT * FROM comments WHERE article_id = 10 ORDER BY name ``` In the case where the `reorder` clause is not used, the SQL executed would be: ```sql -SELECT * FROM articles WHERE id = 10 +SELECT * FROM articles WHERE id = 10 LIMIT 1 SELECT * FROM comments WHERE article_id = 10 ORDER BY posted_at DESC ``` @@ -1080,7 +1091,7 @@ This produces: ```sql SELECT articles.* FROM articles - INNER JOIN categories ON articles.category_id = categories.id + INNER JOIN categories ON categories.id = articles.category_id INNER JOIN comments ON comments.article_id = articles.id ``` @@ -1382,7 +1393,7 @@ end ``` NOTE: The `default_scope` is also applied while creating/building a record -when the scope arguments are given as a `Hash`. It is not applied while +when the scope arguments are given as a `Hash`. It is not applied while updating a record. E.g.: ```ruby @@ -1528,7 +1539,7 @@ Read the full documentation about enums Understanding The Method Chaining --------------------------------- -The Active Record pattern implements [Method Chaining](http://en.wikipedia.org/wiki/Method_chaining), +The Active Record pattern implements [Method Chaining](https://en.wikipedia.org/wiki/Method_chaining), which allow us to use multiple Active Record methods together in a simple and straightforward way. You can chain methods in a statement when the previous method called returns an @@ -1701,10 +1712,10 @@ 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. Instead, you will get 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_hash` 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'") +Client.connection.select_all("SELECT first_name, created_at FROM clients WHERE id = '1'").to_hash # => [ # {"first_name"=>"Rafael", "created_at"=>"2012-11-10 23:23:45.281189"}, # {"first_name"=>"Eileen", "created_at"=>"2013-12-09 11:22:35.221282"} @@ -1860,14 +1871,14 @@ All calculation methods work directly on a model: ```ruby Client.count -# SELECT count(*) AS count_all FROM clients +# SELECT COUNT(*) FROM clients ``` Or on a relation: ```ruby Client.where(first_name: 'Ryan').count -# SELECT count(*) AS count_all FROM clients WHERE (first_name = 'Ryan') +# SELECT COUNT(*) FROM clients WHERE (first_name = 'Ryan') ``` You can also use various finder methods on a relation for performing complex calculations: @@ -1879,9 +1890,9 @@ Client.includes("orders").where(first_name: 'Ryan', orders: { status: 'received' Which will execute: ```sql -SELECT count(DISTINCT clients.id) AS count_all FROM clients - LEFT OUTER JOIN orders ON orders.client_id = clients.id WHERE - (clients.first_name = 'Ryan' AND orders.status = 'received') +SELECT COUNT(DISTINCT clients.id) FROM clients + LEFT OUTER JOIN orders ON orders.client_id = clients.id + WHERE (clients.first_name = 'Ryan' AND orders.status = 'received') ``` ### Count @@ -2034,4 +2045,4 @@ following pointers may be helpful: * MariaDB: [EXPLAIN](https://mariadb.com/kb/en/mariadb/explain/) -* PostgreSQL: [Using EXPLAIN](http://www.postgresql.org/docs/current/static/using-explain.html) +* PostgreSQL: [Using EXPLAIN](https://www.postgresql.org/docs/current/static/using-explain.html) |