Merge pull request rails#47851 from stevehill1981/fix-mysql-check-constraint-schema-dump

Correctly dump check constraints for MySQL 8.0.16+

Author: eileencodes

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -526,7 +526,8 @@ def check_constraints(table_name)
               name: row["name"]
             }
             expression = row["expression"]
-            expression = expression[1..-2] unless mariadb? # remove parentheses added by mysql
+            expression = expression[1..-2] if expression.start_with?("(") && expression.end_with?(")")
+            expression = strip_whitespace_characters(expression)
             CheckConstraintDefinition.new(table_name, expression, options)
           end
         else
@@ -714,6 +715,12 @@ def extract_precision(sql_type)
       EMULATE_BOOLEANS_TRUE = { emulate_booleans: true }.freeze
 
       private
+        def strip_whitespace_characters(expression)
+          expression = expression.gsub(/\\n|\\\\/, "")
+          expression = expression.gsub(/\s{2,}/, " ")
+          expression
+        end
+
         def text_type?(type)
           TYPE_MAP.lookup(type).is_a?(Type::String) || TYPE_MAP.lookup(type).is_a?(Type::Text)
         end

activerecord/test/cases/migration/check_constraint_test.rb

@@ -23,11 +23,21 @@ class Trade < ActiveRecord::Base
             t.integer :price
             t.integer :quantity
           end
+
+          if current_adapter?(:Mysql2Adapter)
+            @connection.create_table "constraint_test", force: true do |t|
+              t.json :options, default: nil
+            end
+          end
         end
 
         teardown do
           @connection.drop_table "trades", if_exists: true rescue nil
           @connection.drop_table "purchases", if_exists: true rescue nil
+
+          if current_adapter?(:Mysql2Adapter)
+            @connection.drop_table "constraint_test", if_exists: true rescue nil
+          end
         end
 
         def test_check_constraints
@@ -44,6 +54,28 @@ def test_check_constraints
             assert_equal "price > discounted_price", constraint.expression
           end
 
+          if current_adapter?(:Mysql2Adapter)
+            begin
+              @connection.add_check_constraint(:constraint_test, <<~SQL,
+                json_contains('
+                  {
+                    "a": 1,
+                    "b": 2,
+                    "c": {
+                      "d": 4
+                    }
+                  }
+                ', options)
+              SQL
+              name: "non_empty_test_array")
+
+              constraint = @connection.check_constraints("constraint_test").find { |c| c.name == "non_empty_test_array" }
+              assert_includes constraint.expression, "json_contains"
+            ensure
+              @connection.remove_check_constraint(:constraint_test, name: "non_empty_test_array", if_exists: true)
+            end
+          end
+
           if current_adapter?(:PostgreSQLAdapter)
             begin
               # Test that complex expression is correctly parsed from the database