DEV: Correct historical posts table schema discrepancies (#10014)

This is a no-op for modern installations. It only affects older sites.

Follow-up to f7d676dce1

This needs to be done in a transaction, because we need to drop and recreate the badge_posts view.

db/post_migrate/20200610150900_correct_posts_schema.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+class CorrectPostsSchema < ActiveRecord::Migration[6.0]
+  # In the past, rails changed the default behavior for varchar columns
+  # This only affects older discourse installations
+  # This migration removes the character limits from posts columns, so that they match modern behavior
+  #
+  # To modify the posts table schema we need to recreate the badge_posts view
+  # This should be done in a transaction
+  def up
+    result = DB.query <<~SQL
+      SELECT character_maximum_length 
+      FROM information_schema.columns 
+      WHERE table_schema='public'
+      AND table_name = 'posts' 
+      AND column_name IN ('action_code', 'edit_reason')
+    SQL
+
+    # No need to continue if the schema is already correct
+    return if result.all? { |r| r.character_maximum_length.nil? }
+
+    execute "DROP VIEW badge_posts"
+
+    execute "ALTER TABLE posts ALTER COLUMN action_code TYPE varchar"
+    execute "ALTER TABLE posts ALTER COLUMN edit_reason TYPE varchar"
+
+    # we must recreate this view every time we amend posts
+    # p.* is auto expanded and persisted into the view definition
+    # at create time
+    execute <<~SQL
+      CREATE VIEW badge_posts AS
+      SELECT p.*
+      FROM posts p
+      JOIN topics t ON t.id = p.topic_id
+      JOIN categories c ON c.id = t.category_id
+      WHERE c.allow_badges AND
+            p.deleted_at IS NULL AND
+            t.deleted_at IS NULL AND
+            NOT c.read_restricted AND
+            t.visible AND
+            p.post_type IN (1,2,3)
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end