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-rw-r--r--guides/source/migrations.md4
1 files changed, 3 insertions, 1 deletions
diff --git a/guides/source/migrations.md b/guides/source/migrations.md
index 62b70b5571..f2aa72492f 100644
--- a/guides/source/migrations.md
+++ b/guides/source/migrations.md
@@ -108,7 +108,9 @@ of the migration. The name of the migration class (CamelCased version)
should match the latter part of the file name. For example
`20080906120000_create_products.rb` should define class `CreateProducts` and
`20080906120001_add_details_to_products.rb` should define
-`AddDetailsToProducts`.
+`AddDetailsToProducts`. Rails uses this timestamp to determine which migration
+should be run and in what order, so if you're copying a migration from another
+application or generate a file yourself, be aware of its position in the order.
Of course, calculating timestamps is no fun, so Active Record provides a
generator to handle making it for you: