1 files changed, 148 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
new file mode 100644
index 0000000000..1cf210d85b
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
@@ -0,0 +1,148 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      module SchemaStatements # :nodoc:
+        # Returns an array of indexes for the given table.
+        def indexes(table_name)
+          indexes = []
+          current_index = nil
+          execute_and_free("SHOW KEYS FROM #{quote_table_name(table_name)}", "SCHEMA") do |result|
+            each_hash(result) do |row|
+              if current_index != row[:Key_name]
+                next if row[:Key_name] == "PRIMARY" # skip the primary key
+                current_index = row[:Key_name]
+
+                mysql_index_type = row[:Index_type].downcase.to_sym
+                case mysql_index_type
+                when :fulltext, :spatial
+                  index_type = mysql_index_type
+                when :btree, :hash
+                  index_using = mysql_index_type
+                end
+
+                indexes << [
+                  row[:Table],
+                  row[:Key_name],
+                  row[:Non_unique].to_i == 0,
+                  [],
+                  lengths: {},
+                  orders: {},
+                  type: index_type,
+                  using: index_using,
+                  comment: row[:Index_comment].presence
+                ]
+              end
+
+              indexes.last[-2] << row[:Column_name]
+              indexes.last[-1][:lengths][row[:Column_name]] = row[:Sub_part].to_i if row[:Sub_part]
+              indexes.last[-1][:orders].merge!(row[:Column_name] => :desc) if row[:Collation] == "D"
+            end
+          end
+
+          indexes.map { |index| IndexDefinition.new(*index) }
+        end
+
+        def remove_column(table_name, column_name, type = nil, options = {})
+          if foreign_key_exists?(table_name, column: column_name)
+            remove_foreign_key(table_name, column: column_name)
+          end
+          super
+        end
+
+        def internal_string_options_for_primary_key
+          super.tap do |options|
+            if CHARSETS_OF_4BYTES_MAXLEN.include?(charset) && (mariadb? || version < "8.0.0")
+              options[:collation] = collation.sub(/\A[^_]+/, "utf8")
+            end
+          end
+        end
+
+        def update_table_definition(table_name, base)
+          MySQL::Table.new(table_name, base)
+        end
+
+        def create_schema_dumper(options)
+          MySQL::SchemaDumper.create(self, options)
+        end
+
+        private
+          CHARSETS_OF_4BYTES_MAXLEN = ["utf8mb4", "utf16", "utf16le", "utf32"]
+
+          def schema_creation
+            MySQL::SchemaCreation.new(self)
+          end
+
+          def create_table_definition(*args)
+            MySQL::TableDefinition.new(*args)
+          end
+
+          def new_column_from_field(table_name, field)
+            type_metadata = fetch_type_metadata(field[:Type], field[:Extra])
+            if type_metadata.type == :datetime && /\ACURRENT_TIMESTAMP(?:\([0-6]?\))?\z/i.match?(field[:Default])
+              default, default_function = nil, field[:Default]
+            else
+              default, default_function = field[:Default], nil
+            end
+
+            MySQL::Column.new(
+              field[:Field],
+              default,
+              type_metadata,
+              field[:Null] == "YES",
+              table_name,
+              default_function,
+              field[:Collation],
+              comment: field[:Comment].presence
+            )
+          end
+
+          def fetch_type_metadata(sql_type, extra = "")
+            MySQL::TypeMetadata.new(super(sql_type), extra: extra)
+          end
+
+          def extract_foreign_key_action(specifier)
+            super unless specifier == "RESTRICT"
+          end
+
+          def add_index_length(quoted_columns, **options)
+            lengths = options_for_index_columns(options[:length])
+            quoted_columns.each do |name, column|
+              column << "(#{lengths[name]})" if lengths[name].present?
+            end
+          end
+
+          def add_options_for_index_columns(quoted_columns, **options)
+            quoted_columns = add_index_length(quoted_columns, options)
+            super
+          end
+
+          def data_source_sql(name = nil, type: nil)
+            scope = quoted_scope(name, type: type)
+
+            sql = "SELECT table_name FROM information_schema.tables".dup
+            sql << " WHERE table_schema = #{scope[:schema]}"
+            sql << " AND table_name = #{scope[:name]}" if scope[:name]
+            sql << " AND table_type = #{scope[:type]}" if scope[:type]
+            sql
+          end
+
+          def quoted_scope(name = nil, type: nil)
+            schema, name = extract_schema_qualified_name(name)
+            scope = {}
+            scope[:schema] = schema ? quote(schema) : "database()"
+            scope[:name] = quote(name) if name
+            scope[:type] = quote(type) if type
+            scope
+          end
+
+          def extract_schema_qualified_name(string)
+            schema, name = string.to_s.scan(/[^`.\s]+|`[^`]*`/)
+            schema, name = nil, schema unless name
+            [schema, name]
+          end
+      end
+    end
+  end
+end