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author | Valery Sizov <vsv2711@gmail.com> | 2015-05-12 11:48:18 +0300 |
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committer | Valery Sizov <vsv2711@gmail.com> | 2015-05-12 14:34:43 +0300 |
commit | 34a9aa2e8a6c3b55e726810f4a899aae23e76363 (patch) | |
tree | a2e800dd8ad02e1507515c9ee1aede6372304976 | |
parent | 9694c8164d8d1ad95fcabe25fb6559e22e9213bc (diff) |
update migration style guide
-rw-r--r-- | doc/development/migration_style_guide.md | 48 |
1 files changed, 47 insertions, 1 deletions
diff --git a/doc/development/migration_style_guide.md b/doc/development/migration_style_guide.md index a102d7987de..4fa1961fde9 100644 --- a/doc/development/migration_style_guide.md +++ b/doc/development/migration_style_guide.md @@ -39,4 +39,50 @@ Your migration should be reversible. This is very important, as it should be possible to downgrade in case of a vulnerability or bugs. In your migration, add a comment describing how the reversibility of the -migration was tested.
\ No newline at end of file +migration was tested. + + +## Removing indices + +If you need to remove index, please add a condition like in following example: + +``` +remove_index :namespaces, column: :name if index_exists?(:namespaces, :name) +``` + +## Adding indices + +If you need to add an unique index please keep in mind there is possibility of existing duplicates. If it is possible write a separate migration for handling this situation. It can be just removing or removing with overwriting all references to these duplicates depend on situation. + +## Testing + +Make sure that your migration works with MySQL and PostgreSQL with data. An empty database does not guarantee that your migration is correct. + +Make sure your migration can be reversed. + +## Data migration + +Please prefer Arel and plain SQL over usual ActiveRecord syntax. In case of using plain SQL you need to quote all input manually with `quote_string` helper. + +Example with Arel: + +``` +users = Arel::Table.new(:users) +users.group(users[:user_id]).having(users[:id].count.gt(5)) + +#updtae other tables with this results +``` + +Example with plain SQL and `quote_string` helper: + +``` +select_all("SELECT name, COUNT(id) as cnt FROM tags GROUP BY name HAVING COUNT(id) > 1").each do |tag| + tag_name = quote_string(tag["name"]) + duplicate_ids = select_all("SELECT id FROM tags WHERE name = '#{tag_name}'").map{|tag| tag["id"]} + origin_tag_id = duplicate_ids.first + duplicate_ids.delete origin_tag_id + + execute("UPDATE taggings SET tag_id = #{origin_tag_id} WHERE tag_id IN(#{duplicate_ids.join(",")})") + execute("DELETE FROM tags WHERE id IN(#{duplicate_ids.join(",")})") +end +``` |