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[DOC] clear up some ambiguity with the way has_and_belongs_to_many cr…

…eates the default join table name. #7072 [jeremymcanally]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5960 5ecf4fe2-1ee6-0310-87b1-e25e094e27de
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commit 56c55354661fcadecb1927fb62fb9038d16e9be1 1 parent 71a4f71
@technoweenie technoweenie authored
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2  activerecord/CHANGELOG
@@ -1,5 +1,7 @@
*SVN*
+* [DOC] clear up some ambiguity with the way has_and_belongs_to_many creates the default join table name. #7072 [jeremymcanally]
+
* change_column accepts :default => nil. Skip column options for primary keys. #6956, #7048 [dcmanges, Jeremy Kemper]
* MySQL, PostgreSQL: change_column_default quotes the default value and doesn't lose column type information. #3987, #6664 [Jonathan Viney, manfred, altano@bigfoot.com]
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8 activerecord/lib/active_record/associations.rb
@@ -809,7 +809,13 @@ def belongs_to(association_id, options = {})
# Associates two classes via an intermediate join table. Unless the join table is explicitly specified as
# an option, it is guessed using the lexical order of the class names. So a join between Developer and Project
- # will give the default join table name of "developers_projects" because "D" outranks "P".
+ # will give the default join table name of "developers_projects" because "D" outranks "P". Note that this precedence
+ # is calculated using the <tt><</tt> operator for <tt>String</tt>. This means that if the strings are of different lengths,
+ # and the strings are equal when compared up to the shortest length, then the longer string is considered of higher
+ # lexical precedence than the shorter one. For example, one would expect the tables <tt>paper_boxes</tt> and <tt>papers</tt>
+ # to generate a join table name of <tt>papers_paper_boxes</tt> because of the length of the name <tt>paper_boxes</tt>,
+ # but it in fact generates a join table name of <tt>paper_boxes_papers</tt>. Be aware of this caveat, and use the
+ # custom <tt>join_table</tt> option if you need to.
#
# Deprecated: Any additional fields added to the join table will be placed as attributes when pulling records out through
# has_and_belongs_to_many associations. Records returned from join tables with additional attributes will be marked as

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