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Merge pull request #22705 from RochesterinNYC/add-order-explanation-to-first-last-guides

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Add clarification about `first` and `last` behavior when using `order` [ci skip]
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Jon Moss 2016-01-18 10:31:39 -05:00
commit 5f302eabae
1 changed files with 28 additions and 2 deletions
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30
guides/source/active_record_querying.md
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@ -170,7 +170,7 @@ TIP: The retrieved record may vary depending on the database engine.
#### `first`
The `first` method finds the first record ordered by the primary key. For example:
The `first` method finds the first record ordered by primary key (default). For example:
```ruby
client = Client.first
@ -204,11 +204,24 @@ The SQL equivalent of the above is:
SELECT * FROM clients ORDER BY clients.id ASC LIMIT 3
```
On a collection that is ordered using `order`, `first` will return the first record ordered by the specified attribute for `order`.
```ruby
client = Client.order(:first_name).first
# => #<Client id: 2, first_name: "Fifo">
```
The SQL equivalent of the above is:
```sql
SELECT * FROM clients ORDER BY clients.first_name ASC LIMIT 1
```
The `first!` method behaves exactly like `first`, except that it will raise `ActiveRecord::RecordNotFound` if no matching record is found.
#### `last`
The `last` method finds the last record ordered by the primary key. For example:
The `last` method finds the last record ordered by primary key (default). For example:
```ruby
client = Client.last
@ -242,6 +255,19 @@ The SQL equivalent of the above is:
SELECT * FROM clients ORDER BY clients.id DESC LIMIT 3
```
On a collection that is ordered using `order`, `last` will return the last record ordered by the specified attribute for `order`.
```ruby
client = Client.order(:first_name).last
# => #<Client id: 220, first_name: "Sara">
```
The SQL equivalent of the above is:
```sql
SELECT * FROM clients ORDER BY clients.first_name DESC LIMIT 1
```
The `last!` method behaves exactly like `last`, except that it will raise `ActiveRecord::RecordNotFound` if no matching record is found.
#### `find_by`