[DOC] clear up some ambiguity with the way has_and_belongs_to_many creates the default join table name. #7072 [jeremymcanally]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5960 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

2 files changed, 9 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index 32d977a11d..ef2263a855 100644
--- a/activerecord/CHANGELOG
+++ b/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]
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index f1c274af42..4f251077ed 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -809,7 +809,13 @@ module ActiveRecord
 
       # 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