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Description: Ruby on Rails
Homepage: http://rubyonrails.org
Clone URL: git://github.com/rails/rails.git 
Cache migrated versions list in Migrator and use it to fetch the latest migrated 
version name [#845 state:resolved]

Also optimized Migrator#current_version class method to fetch
only the latest version number and not all of them.

With this change no matter how many migrations there are the
schema_migrations table is only SELECTed from once.

Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>
Tarmo Tänav (author)
Mon Aug 25 18:55:57 -0700 2008
jeremy (committer)
Mon Aug 25 22:03:47 -0700 2008
commit  3d2ac918b987ef0cff34f6a7fdd20926b7a9e5d9
tree    c59dd78994dd9892c0707947d4e02d6c79b2556d
parent  4bcd64c9e93af2f13dc7309cd76bb764e4d7d23d
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activerecord/lib/active_record/migration.rb 
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@@ -407,10 +407,9 @@ module ActiveRecord
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       end
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       def current_version
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-        version = Base.connection.select_values(
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-          "SELECT version FROM #{schema_migrations_table_name}"
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-        ).map(&:to_i).max rescue nil
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-        version || 0
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+        Base.connection.select_value(
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+          "SELECT MAX(CAST(version AS integer)) FROM #{schema_migrations_table_name}"
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+        ).to_i rescue 0
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       end
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       def proper_table_name(name)
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@@ -426,7 +425,7 @@ module ActiveRecord
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     end
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     def current_version
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-      self.class.current_version
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+      migrated.last || 0
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     end
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     def current_migration
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@@ -518,16 +517,19 @@ module ActiveRecord
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     def migrated
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       sm_table = self.class.schema_migrations_table_name
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-      Base.connection.select_values("SELECT version FROM #{sm_table}").map(&:to_i).sort
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+      @migrated_versions ||= Base.connection.select_values("SELECT version FROM #{sm_table}").map(&:to_i).sort
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     end
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     private
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       def record_version_state_after_migrating(version)
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         sm_table = self.class.schema_migrations_table_name
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+        @migrated_versions ||= []
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         if down?
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+          @migrated_versions.delete(version.to_i)
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           Base.connection.update("DELETE FROM #{sm_table} WHERE version = '#{version}'")
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         else
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+          @migrated_versions.push(version.to_i).sort!
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           Base.connection.insert("INSERT INTO #{sm_table} (version) VALUES ('#{version}')")
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         end
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       end

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