Merge pull request #42429 from Flixt/fix-mysql-check-constraints-quoting

Fix duplicate escaping of quotes for check constraint expressions in MySQL schema

activerecord/CHANGELOG.md

@@ -1,3 +1,12 @@
+*   Fix duplicate quoting for check constraint expressions in schema dump when using MySQL
+
+    A check constraint with an expression, that already contains quotes, lead to an invalid schema
+    dump with the mysql2 adapter.
+
+    Fixes #42424.
+
+    *Felix Tscheulin*
+
 *   Performance tune the SQLite3 adapter connection configuration
 
     For Rails applications, the Write-Ahead-Log in normal syncing mode with a capped journal size, a healthy shared memory buffer and a shared cache will perform, on average, 2× better.

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -531,6 +531,13 @@ def check_constraints(table_name)
             expression = row["expression"]
             expression = expression[1..-2] if expression.start_with?("(") && expression.end_with?(")")
             expression = strip_whitespace_characters(expression)
+
+            unless mariadb?
+              # MySQL returns check constraints expression in an already escaped form.
+              # This leads to duplicate escaping later (e.g. when the expression is used in the SchemaDumper).
+              expression = expression.gsub("\\'", "'")
+            end
+
             CheckConstraintDefinition.new(table_name, expression, options)
           end
         else

activerecord/test/cases/adapters/mysql2/check_constraint_quoting_test.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/schema_dumping_helper"
+
+if ActiveRecord::Base.connection.supports_check_constraints?
+  class Mysql2CheckConstraintQuotingTest < ActiveRecord::Mysql2TestCase
+    include SchemaDumpingHelper
+
+    setup do
+      @connection = ActiveRecord::Base.connection
+      @connection.create_table "trades", force: true do |t|
+        t.string :name
+      end
+    end
+
+    teardown do
+      @connection.drop_table "trades", if_exists: true rescue nil
+    end
+
+    def test_check_constraint_no_duplicate_expression_quoting
+      @connection.add_check_constraint :trades, "name != 'forbidden_string'"
+
+      check_constraints = @connection.check_constraints("trades")
+      assert_equal 1, check_constraints.size
+
+      expression = check_constraints.first.expression
+      if ActiveRecord::Base.connection.mariadb?
+        assert_equal "`name` <> 'forbidden_string'", expression
+      else
+        assert_equal "`name` <> _utf8mb4'forbidden_string'", expression
+      end
+    end
+  end
+end