Introduce drop-table-only feature

Basically, dropping tables are very dangerous operation. So
Ridgepole disables drop tables by default.

But of course we need to do drop sometimes.  In that case, I would
like to run only `drop tables` to avoid unexpected changes.
This PR implements the feature for that.

README.md

@@ -82,6 +82,7 @@ Usage: ridgepole [options]
         --dump-with-default-fk-name
         --index-removed-drop-column
         --drop-table
+        --drop-table-only
         --mysql-change-table-options
         --mysql-change-table-comment
         --check-relation-type DEF_PK

bin/ridgepole

@@ -137,6 +137,7 @@ ARGV.options do |opt|
   opt.on('',   '--dump-with-default-fk-name') { options[:dump_with_default_fk_name] = true }
   opt.on('',   '--index-removed-drop-column') { options[:index_removed_drop_column] = true }
   opt.on('',   '--drop-table') { options[:force_drop_table] = true }
+  opt.on('',   '--drop-table-only') { options[:drop_table_only] = true }
   opt.on('',   '--mysql-change-table-options') { options[:mysql_change_table_options] = true }
   opt.on('',   '--mysql-change-table-comment') { options[:mysql_change_table_comment] = true }
   opt.on('',   '--check-relation-type DEF_PK') { |v| options[:check_relation_type] = v }

lib/ridgepole/diff.rb

@@ -28,20 +28,22 @@ def diff(from, to, options = {})
         if (from_attrs = from.delete(table_name))
           @logger.verbose_info("#   #{table_name}")
 
-          unless (attrs_delta = diff_inspect(from_attrs, to_attrs)).empty?
-            @logger.verbose_info(attrs_delta)
-          end
+          unless @options[:drop_table_only]
+            unless (attrs_delta = diff_inspect(from_attrs, to_attrs)).empty?
+              @logger.verbose_info(attrs_delta)
+            end
 
-          scan_change(table_name, from_attrs, to_attrs, delta)
-        else
+            scan_change(table_name, from_attrs, to_attrs, delta)
+          end
+        elsif !@options[:drop_table_only]
           delta[:add] ||= {}
           delta[:add][table_name] = to_attrs
         end
       end
 
       scan_relation_info(relation_info)
 
-      if !@options[:merge] && @options[:force_drop_table]
+      if !@options[:merge] && (@options[:force_drop_table] || @options[:drop_table_only])
         from.each do |table_name, from_attrs|
           next unless target?(table_name)
 

spec/mysql/cli/ridgepole_spec.rb

@@ -48,6 +48,7 @@ def conn_spec_str(database)
             --dump-with-default-fk-name
             --index-removed-drop-column
             --drop-table
+            --drop-table-only
             --mysql-change-table-options
             --mysql-change-table-comment
             --check-relation-type DEF_PK

spec/mysql/migrate/migrate_drop_table_only_spec.rb

@@ -0,0 +1,135 @@
+# frozen_string_literal: true
+
+describe 'Ridgepole::Client#diff -> migrate' do
+  context 'when drop table only' do
+    let(:dsl) do
+      erbh(<<-ERB)
+        create_table "clubs", force: :cascade do |t|
+          t.string "name", default: "", null: false
+          t.index ["name"], name: "idx_name", unique: true
+        end
+
+        create_table "departments", primary_key: "dept_no", force: :cascade do |t|
+          t.string "dept_name", limit: 40, null: false
+          t.index ["dept_name"], name: "dept_name", unique: true
+        end
+
+        create_table "dept_emp", id: false, force: :cascade do |t|
+          t.integer "emp_no", null: false
+          t.string  "dept_no", null: false
+          t.date    "from_date", null: false
+          t.date    "to_date", null: false
+          t.index ["dept_no"], name: "dept_no"
+          t.index ["emp_no"], name: "emp_no"
+        end
+
+        create_table "dept_manager", id: false, force: :cascade do |t|
+          t.string  "dept_no", null: false
+          t.integer "emp_no", null: false
+          t.date    "from_date", null: false
+          t.date    "to_date", null: false
+          t.index ["dept_no"], name: "dept_no"
+          t.index ["emp_no"], name: "emp_no"
+        end
+
+        create_table "employee_clubs", force: :cascade do |t|
+          t.integer "emp_no", null: false
+          t.integer "club_id", null: false
+          t.index ["emp_no", "club_id"], name: "idx_emp_no_club_id"
+        end
+
+        create_table "employees", primary_key: "emp_no", force: :cascade do |t|
+          t.date   "birth_date", null: false
+          t.string "first_name", limit: 14, null: false
+          t.string "last_name", limit: 16, null: false
+          t.string "gender", limit: 1, null: false
+          t.date   "hire_date", null: false
+        end
+      ERB
+    end
+
+    let(:migrate_dsl) do
+      erbh(<<-ERB)
+        create_table "departments", primary_key: "dept_no", force: :cascade do |t|
+          t.string "dept_name", limit: 40, null: false
+          t.date    "from_date", null: false
+          t.date    "to_date", null: false
+          t.index ["dept_name"], name: "dept_name", unique: true
+        end
+
+        create_table "dept_manager", id: false, force: :cascade do |t|
+          t.string  "dept_no", null: false
+          t.integer "emp_no", null: false
+          t.index ["dept_no"], name: "dept_no"
+          t.index ["emp_no"], name: "emp_no"
+        end
+
+        create_table "employee_clubs", force: :cascade do |t|
+          t.string "emp_no", null: false
+          t.integer "club_id", null: false
+          t.index ["emp_no", "club_id"], name: "idx_emp_no_club_id"
+        end
+
+        create_table "employees", primary_key: "emp_no", force: :cascade do |t|
+          t.date   "birth_date", null: false
+          t.string "first_name", limit: 14, null: false
+          t.string "last_name", limit: 16, null: false
+          t.string "gender", limit: 1, null: false
+          t.date   "hire_date", null: false
+        end
+
+        create_table "salaries", id: false, force: :cascade do |t|
+          t.integer "emp_no", null: false
+          t.integer "salary", null: false
+          t.date    "from_date", null: false
+          t.date    "to_date", null: false
+        end
+
+        add_index "salaries", ["emp_no"], name: "emp_no", using: :btree
+      ERB
+    end
+
+    let(:expected_dsl) do
+      erbh(<<-ERB)
+        create_table "departments", primary_key: "dept_no", force: :cascade do |t|
+          t.string "dept_name", limit: 40, null: false
+          t.index ["dept_name"], name: "dept_name", unique: true
+        end
+
+        create_table "dept_manager", id: false, force: :cascade do |t|
+          t.string  "dept_no", null: false
+          t.integer "emp_no", null: false
+          t.date    "from_date", null: false
+          t.date    "to_date", null: false
+          t.index ["dept_no"], name: "dept_no"
+          t.index ["emp_no"], name: "emp_no"
+        end
+
+        create_table "employee_clubs", force: :cascade do |t|
+          t.integer "emp_no", null: false
+          t.integer "club_id", null: false
+          t.index ["emp_no", "club_id"], name: "idx_emp_no_club_id"
+        end
+
+        create_table "employees", primary_key: "emp_no", force: :cascade do |t|
+          t.date   "birth_date", null: false
+          t.string "first_name", limit: 14, null: false
+          t.string "last_name", limit: 16, null: false
+          t.string "gender", limit: 1, null: false
+          t.date   "hire_date", null: false
+        end
+      ERB
+    end
+
+    before { client.diff(dsl).migrate }
+    subject { client(drop_table_only: true) }
+
+    it {
+      delta = subject.diff(migrate_dsl)
+      expect(delta.differ?).to be_truthy
+      expect(subject.dump).to match_ruby dsl
+      delta.migrate
+      expect(subject.dump).to match_ruby expected_dsl
+    }
+  end
+end