diff options
Diffstat (limited to 'guides/source/active_record_querying.textile')
| -rw-r--r-- | guides/source/active_record_querying.textile | 84 |
1 files changed, 53 insertions, 31 deletions
diff --git a/guides/source/active_record_querying.textile b/guides/source/active_record_querying.textile index 58eae2ee0f..a9cb424eaa 100644 --- a/guides/source/active_record_querying.textile +++ b/guides/source/active_record_querying.textile @@ -99,9 +99,28 @@ SELECT * FROM clients WHERE (clients.id = 10) LIMIT 1 <tt>Model.find(primary_key)</tt> will raise an +ActiveRecord::RecordNotFound+ exception if no matching record is found. +h5. +take+ + +<tt>Model.take</tt> retrieves a record without any implicit ordering. For example: + +<ruby> +client = Client.take +# => #<Client id: 1, first_name: "Lifo"> +</ruby> + +The SQL equivalent of the above is: + +<sql> +SELECT * FROM clients LIMIT 1 +</sql> + +<tt>Model.take</tt> returns +nil+ if no record is found and no exception will be raised. + +TIP: The retrieved record may vary depending on the database engine. + h5. +first+ -<tt>Model.first</tt> finds the first record matched by the supplied options, if any. For example: +<tt>Model.first</tt> finds the first record ordered by the primary key. For example: <ruby> client = Client.first @@ -111,14 +130,14 @@ client = Client.first The SQL equivalent of the above is: <sql> -SELECT * FROM clients LIMIT 1 +SELECT * FROM clients ORDER BY clients.id ASC LIMIT 1 </sql> -<tt>Model.first</tt> returns +nil+ if no matching record is found. No exception will be raised. +<tt>Model.first</tt> returns +nil+ if no matching record is found and no exception will be raised. h5. +last+ -<tt>Model.last</tt> finds the last record matched by the supplied options. For example: +<tt>Model.last</tt> finds the last record ordered by the primary key. For example: <ruby> client = Client.last @@ -131,7 +150,7 @@ The SQL equivalent of the above is: SELECT * FROM clients ORDER BY clients.id DESC LIMIT 1 </sql> -<tt>Model.last</tt> returns +nil+ if no matching record is found. No exception will be raised. +<tt>Model.last</tt> returns +nil+ if no matching record is found and no exception will be raised. h5. +find_by+ @@ -148,12 +167,29 @@ Client.find_by first_name: 'Jon' It is equivalent to writing: <ruby> -Client.where(first_name: 'Lifo').first +Client.where(first_name: 'Lifo').take +</ruby> + +h5(#take_1). +take!+ + +<tt>Model.take!</tt> retrieves a record without any implicit ordering. For example: + +<ruby> +client = Client.take! +# => #<Client id: 1, first_name: "Lifo"> </ruby> +The SQL equivalent of the above is: + +<sql> +SELECT * FROM clients LIMIT 1 +</sql> + +<tt>Model.take!</tt> raises +ActiveRecord::RecordNotFound+ if no matching record is found. + h5(#first_1). +first!+ -<tt>Model.first!</tt> finds the first record. For example: +<tt>Model.first!</tt> finds the first record ordered by the primary key. For example: <ruby> client = Client.first! @@ -163,14 +199,14 @@ client = Client.first! The SQL equivalent of the above is: <sql> -SELECT * FROM clients LIMIT 1 +SELECT * FROM clients ORDER BY clients.id ASC LIMIT 1 </sql> -<tt>Model.first!</tt> raises +RecordNotFound+ if no matching record is found. +<tt>Model.first!</tt> raises +ActiveRecord::RecordNotFound+ if no matching record is found. h5(#last_1). +last!+ -<tt>Model.last!</tt> finds the last record. For example: +<tt>Model.last!</tt> finds the last record ordered by the primary key. For example: <ruby> client = Client.last! @@ -183,24 +219,24 @@ The SQL equivalent of the above is: SELECT * FROM clients ORDER BY clients.id DESC LIMIT 1 </sql> -<tt>Model.last!</tt> raises +RecordNotFound+ if no matching record is found. +<tt>Model.last!</tt> raises +ActiveRecord::RecordNotFound+ if no matching record is found. h5(#find_by_1). +find_by!+ -<tt>Model.find_by!</tt> finds the first record matching some conditions. It raises +RecordNotFound+ if no matching record is found. For example: +<tt>Model.find_by!</tt> finds the first record matching some conditions. It raises +ActiveRecord::RecordNotFound+ if no matching record is found. For example: <ruby> Client.find_by! first_name: 'Lifo' # => #<Client id: 1, first_name: "Lifo"> Client.find_by! first_name: 'Jon' -# => RecordNotFound +# => ActiveRecord::RecordNotFound </ruby> It is equivalent to writing: <ruby> -Client.where(first_name: 'Lifo').first! +Client.where(first_name: 'Lifo').take! </ruby> h4. Retrieving Multiple Objects @@ -356,20 +392,6 @@ Client.where("created_at >= :start_date AND created_at <= :end_date", This makes for clearer readability if you have a large number of variable conditions. -h5(#array-range_conditions). Range Conditions - -If you're looking for a range inside of a table (for example, users created in a certain timeframe) you can use the conditions option coupled with the +IN+ SQL statement for this. If you had two dates coming in from a controller you could do something like this to look for a range: - -<ruby> -Client.where(:created_at => (params[:start_date].to_date)..(params[:end_date].to_date)) -</ruby> - -This query will generate something similar to the following SQL: - -<sql> - SELECT "clients".* FROM "clients" WHERE ("clients"."created_at" BETWEEN '2010-09-29' AND '2010-11-30') -</sql> - h4. Hash Conditions Active Record also allows you to pass in hash conditions which can increase the readability of your conditions syntax. With hash conditions, you pass in a hash with keys of the fields you want conditionalised and the values of how you want to conditionalise them: @@ -388,9 +410,9 @@ The field name can also be a string: Client.where('locked' => true) </ruby> -h5(#hash-range_conditions). Range Conditions +NOTE: The values cannot be symbols. For example, you cannot do +Client.where(:status => :active)+. -The good thing about this is that we can pass in a range for our fields without it generating a large query as shown in the preamble of this section. +h5(#hash-range_conditions). Range Conditions <ruby> Client.where(:created_at => (Time.now.midnight - 1.day)..Time.now.midnight) @@ -924,7 +946,7 @@ This code looks fine at the first sight. But the problem lies within the total n Active Record lets you specify in advance all the associations that are going to be loaded. This is possible by specifying the +includes+ method of the +Model.find+ call. With +includes+, Active Record ensures that all of the specified associations are loaded using the minimum possible number of queries. -Revisiting the above case, we could rewrite +Client.all+ to use eager load addresses: +Revisiting the above case, we could rewrite +Client.limit(10)+ to use eager load addresses: <ruby> clients = Client.includes(:address).limit(10) |