DEV: remove exec_sql and replace with mini_sql

Introduce new patterns for direct sql that are safe and fast.

MiniSql is not prone to memory bloat that can happen with direct PG usage.
It also has an extremely fast materializer and very a convenient API

- DB.exec(sql, *params) => runs sql returns row count
- DB.query(sql, *params) => runs sql returns usable objects (not a hash)
- DB.query_hash(sql, *params) => runs sql returns an array of hashes
- DB.query_single(sql, *params) => runs sql and returns a flat one dimensional array
- DB.build(sql) => returns a sql builder

See more at: https://github.com/discourse/mini_sql

db/fixtures/000_delayed_drops.rb

@@ -48,7 +48,7 @@ Migration::ColumnDropper.drop(
   },
   on_drop: ->() {
     STDERR.puts "Removing superflous user stats columns!"
-    ActiveRecord::Base.exec_sql "DROP FUNCTION IF EXISTS first_unread_topic_for(int)"
+    DB.exec "DROP FUNCTION IF EXISTS first_unread_topic_for(int)"
   }
 )
 

db/fixtures/001_categories.rb

@@ -10,18 +10,18 @@ uncat_id = -1 unless Numeric === uncat_id
 if uncat_id == -1 || !Category.exists?(uncat_id)
   puts "Seeding uncategorized category!"
 
-  result = Category.exec_sql "SELECT 1 FROM categories WHERE lower(name) = 'uncategorized'"
+  count = DB.exec "SELECT 1 FROM categories WHERE lower(name) = 'uncategorized'"
   name = 'Uncategorized'
-  name << SecureRandom.hex if result.count > 0
+  name << SecureRandom.hex if count > 0
 
-  result = Category.exec_sql "INSERT INTO categories
+  result = DB.query_single "INSERT INTO categories
           (name,color,slug,description,text_color, user_id, created_at, updated_at, position, name_lower)
    VALUES ('#{name}', 'AB9364', 'uncategorized', '', 'FFFFFF', -1, now(), now(), 1, '#{name.downcase}' )
    RETURNING id
   "
-  category_id = result[0]["id"].to_i
+  category_id = result.first.to_i
 
-  Category.exec_sql "DELETE FROM site_settings where name = 'uncategorized_category_id'"
-  Category.exec_sql "INSERT INTO site_settings(name, data_type, value, created_at, updated_at)
+  DB.exec "DELETE FROM site_settings where name = 'uncategorized_category_id'"
+  DB.exec "INSERT INTO site_settings(name, data_type, value, created_at, updated_at)
            VALUES ('uncategorized_category_id', 3, #{category_id}, now(), now())"
 end

db/fixtures/006_badges.rb

@@ -31,7 +31,7 @@ BadgeGrouping.seed do |g|
 end
 
 # BUGFIX
-Badge.exec_sql <<-SQL.squish
+DB.exec <<-SQL.squish
   UPDATE badges
      SET badge_grouping_id = -1
    WHERE NOT EXISTS (

db/fixtures/500_lounge_category.rb

@@ -36,7 +36,7 @@ unless Rails.env.test?
         end
 
         # Reset topic count because we don't count the description topic
-        Category.exec_sql "UPDATE categories SET topic_count = 0 WHERE id = #{lounge.id}"
+        DB.exec "UPDATE categories SET topic_count = 0 WHERE id = #{lounge.id}"
       end
     end
   end

db/fixtures/501_meta_category.rb

@@ -25,7 +25,7 @@ unless Rails.env.test?
       end
 
       # Reset topic count because we don't count the description topic
-      Category.exec_sql "UPDATE categories SET topic_count = 0 WHERE id = #{meta.id}"
+      DB.exec "UPDATE categories SET topic_count = 0 WHERE id = #{meta.id}"
     end
   end
 end

db/fixtures/502_staff_category.rb

@@ -33,7 +33,7 @@ unless Rails.env.test?
         end
 
         # Reset topic count because we don't count the description topic
-        Category.exec_sql "UPDATE categories SET topic_count = 0 WHERE id = #{staff.id}"
+        DB.exec "UPDATE categories SET topic_count = 0 WHERE id = #{staff.id}"
       end
     end
   end