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Revert "Revert "[AR querying guide] Add examples for take(limit), first(limit) and last(limit)""

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This reverts commit 5559a2ae98.

Reason: These are for selecting multiple objects and there isn't a need
to club them with the selecting single objects section, as discussed
with the author.
This commit is contained in:
Vijay Dev 2012-05-30 23:05:48 +05:30
parent ec74763c39
commit 3b6d66a0c8
1 changed files with 48 additions and 0 deletions
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guides/source/active_record_querying.textile
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@ -259,6 +259,54 @@ SELECT * FROM clients WHERE (clients.id IN (1,10))
WARNING: <tt>Model.find(array_of_primary_key)</tt> will raise an +ActiveRecord::RecordNotFound+ exception unless a matching record is found for <strong>all</strong> of the supplied primary keys. WARNING: <tt>Model.find(array_of_primary_key)</tt> will raise an +ActiveRecord::RecordNotFound+ exception unless a matching record is found for <strong>all</strong> of the supplied primary keys.
h5. take
<tt>Model.take(limit)</tt> retrieves the first number of records specified by +limit+ without any explicit ordering:
<ruby>
Client.take(2)
# => [#<Client id: 1, first_name: "Lifo">,
#<Client id: 2, first_name: "Raf">]
</ruby>
The SQL equivalent of the above is:
<sql>
SELECT * FROM clients LIMIT 2
</sql>
h5. first
<tt>Model.first(limit)</tt> finds the first number of records specified by +limit+ ordered by primary key:
<ruby>
Client.first(2)
# => [#<Client id: 1, first_name: "Lifo">,
#<Client id: 2, first_name: "Raf">]
</ruby>
The SQL equivalent of the above is:
<sql>
SELECT * FROM clients LIMIT 2
</sql>
h5. last
<tt>Model.last(limit)</tt> finds the number of records specified by +limit+ ordered by primary key in descending order:
<ruby>
Client.last(2)
# => [#<Client id: 10, first_name: "Ryan">,
#<Client id: 9, first_name: "John">]
</ruby>
The SQL equivalent of the above is:
<sql>
SELECT * FROM clients ORDER By id DESC LIMIT 2
</sql>
h4. Retrieving Multiple Objects in Batches h4. Retrieving Multiple Objects in Batches
We often need to iterate over a large set of records, as when we send a newsletter to a large set of users, or when we export data. We often need to iterate over a large set of records, as when we send a newsletter to a large set of users, or when we export data.