Merge pull request rails#54707 from fatkodima/query_log_tags_prepend_comment

Expose ability to prepend query log tags via application configuration

Author: fatkodima

activerecord/lib/active_record/query_logs.rb

@@ -65,7 +65,7 @@ module ActiveRecord
   #
   # Tag comments can be prepended to the query:
   #
-  #    ActiveRecord::QueryLogs.prepend_comment = true
+  #     config.active_record.query_log_tags_prepend_comment = true
   #
   # For applications where the content will not change during the lifetime of
   # the request or job execution, the tags can be cached for reuse in every query:

activerecord/lib/active_record/railtie.rb

@@ -35,6 +35,7 @@ class Railtie < Rails::Railtie # :nodoc:
     config.active_record.query_log_tags = [ :application ]
     config.active_record.query_log_tags_format = :legacy
     config.active_record.cache_query_log_tags = false
+    config.active_record.query_log_tags_prepend_comment = false
     config.active_record.raise_on_assign_to_attr_readonly = false
     config.active_record.belongs_to_required_validates_foreign_key = true
     config.active_record.generate_secure_token_on = :create
@@ -230,6 +231,7 @@ class Railtie < Rails::Railtie # :nodoc:
           :query_log_tags,
           :query_log_tags_format,
           :cache_query_log_tags,
+          :query_log_tags_prepend_comment,
           :sqlite3_adapter_strict_strings_by_default,
           :check_schema_cache_dump_version,
           :use_schema_cache_dump,
@@ -398,6 +400,10 @@ class Railtie < Rails::Railtie # :nodoc:
           if app.config.active_record.cache_query_log_tags
             ActiveRecord::QueryLogs.cache_query_log_tags = true
           end
+
+          if app.config.active_record.query_log_tags_prepend_comment
+            ActiveRecord::QueryLogs.prepend_comment = true
+          end
         end
       end
     end

guides/source/configuring.md

@@ -1540,6 +1540,17 @@ that have a large number of queries, caching query log tags can provide a
 performance benefit when the context does not change during the lifetime of the
 request or job execution. Defaults to `false`.
 
+#### `config.active_record.query_log_tags_prepend_comment`
+
+Specifies whether or not to prepend query log tags comment to the query.
+
+By default comments are appended at the end of the query. Certain databases, such as MySQL will
+truncate the query text. This is the case for slow query logs and the results of querying
+some InnoDB internal tables where the length of the query is more than 1024 bytes.
+In order to not lose the log tags comments from the queries, you can prepend the comments using this option.
+
+Defaults to `false`.
+
 #### `config.active_record.schema_cache_ignored_tables`
 
 Define the list of table that should be ignored when generating the schema

railties/test/application/query_logs_test.rb

@@ -19,7 +19,7 @@ class User < ActiveRecord::Base
       app_file "app/controllers/users_controller.rb", <<-RUBY
         class UsersController < ApplicationController
           def index
-            render inline: ActiveRecord::QueryLogs.call("", Pet.connection)
+            render inline: ActiveRecord::QueryLogs.call("SELECT 1", Pet.connection)
           end
 
           def dynamic_content
@@ -146,7 +146,7 @@ def app
       get "/", {}, { "HTTPS" => "on" }
       comment = last_response.body.strip
 
-      assert_equal("/*action='index',controller='users',database='storage%2Fproduction_animals.sqlite3'*/", comment)
+      assert_equal("SELECT 1 /*action='index',controller='users',database='storage%2Fproduction_animals.sqlite3'*/", comment)
     end
 
     test "source_location information is added if enabled" do
@@ -166,6 +166,19 @@ def app
       assert_match(/source_location='.*\d+'/, comment)
     end
 
+    test "prepending tags comment" do
+      add_to_config "config.active_record.query_log_tags_enabled = true"
+      add_to_config "config.active_record.query_log_tags = [ :action, :controller ]"
+      add_to_config "config.active_record.query_log_tags_prepend_comment = true"
+
+      boot_app
+
+      get "/", {}, { "HTTPS" => "on" }
+      comment = last_response.body.strip
+
+      assert_match(/\A\/\*action='index',controller='users'\*\/ SELECT 1/, comment)
+    end
+
     test "controller tags are not doubled up if already configured" do
       add_to_config "config.active_record.query_log_tags_enabled = true"
       add_to_config "config.active_record.query_log_tags = [ :action, :job, :controller, :pid ]"
@@ -261,7 +274,7 @@ def app
 
       get "/", {}, { "HTTPS" => "on" }
       comment = last_response.body.strip
-      assert_equal %(/*action='index',controller='users',namespaced_controller='users'*/), comment
+      assert_equal %(SELECT 1 /*action='index',controller='users',namespaced_controller='users'*/), comment
 
       get "/namespaced/users", {}, { "HTTPS" => "on" }
       comment = last_response.body.strip