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[AR querying guide] Add examples for take(limit), first(limit) and la…

…st(limit)
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1 parent 501d98b commit 724d6fa6bb48b61798c223b47dd27155839c40d5 @rafmagana rafmagana committed May 28, 2012
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  1. +48 −0 guides/source/active_record_querying.textile
@@ -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.
+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
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.

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