这是我的迁移文件
class CreateDatabaseStructure < ActiveRecord::Migration
def up
create_table "categories", force: true do |t|
t.string "name", null: false
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "cities", force: true do |t|
t.integer "country_id", null: false
t.integer "region_id", null: false
t.string "name", null: false
t.float "Latitude", null: false
t.float "Longitude", null: false
t.string "TimeZone", limit: 10, null: false
t.integer "DmaId", limit: 2
t.string "County", limit: 25
t.string "Code", limit: 4
end
create_table "countries", force: true do |t|
t.string "name", null: false
t.string "FIPS104", limit: 2, null: false
t.string "ISO2", limit: 2, null: false
t.string "ISO3", limit: 3, null: false
t.string "ISON", limit: 4, null: false
t.string "Internet", limit: 2, null: false
t.string "Capital", limit: 25
t.string "MapReference", limit: 50
t.string "NationalitySingular", limit: 35
t.string "NationalityPlural", limit: 35
t.string "Currency", limit: 30
t.string "CurrencyCode", limit: 3
t.integer "Population", limit: 8
t.string "Title", limit: 50
t.string "Comment"
end
end
def down
drop_table :categories, :countries
#drop_table :venues
end
end
当我运行命令rake db:migrate:down VERSION=20140618100702时，我收到以下错误。
== 20140618100702 CreateDatabaseStructure: reverting ==========================
-- drop_table(:categories, :countries)
rake aborted!
StandardError: An error has occurred:
no implicit conversion of Symbol into Integer/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:486:in `[]'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:486:in `drop_table'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:649:in `block in method_missing'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:621:in `block in say_with_time'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:621:in `say_with_time'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:641:in `method_missing'
/Users/harshamv/Sites/nomad/db/migrate/20140618100702_create_database_structure.rb:176:in `down'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:598:in `exec_migration'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:579:in `block (2 levels) in migrate'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:578:in `block in migrate'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:577:in `migrate'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:752:in `migrate'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:992:in `block in execute_migration_in_transaction'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:1040:in `ddl_transaction'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:991:in `execute_migration_in_transaction'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:936:in `run'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:818:in `run'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/railties/databases.rake:79:in `block (3 levels) in <top (required)>'
/Users/harshamv/.rvm/gems/ruby-2.1.2/bin/ruby_executable_hooks:15:in `eval'
/Users/harshamv/.rvm/gems/ruby-2.1.2/bin/ruby_executable_hooks:15:in `<main>'
TypeError: no implicit conversion of Symbol into Integer
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:486:in `[]'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:486:in `drop_table'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:649:in `block in method_missing'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:621:in `block in say_with_time'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:621:in `say_with_time'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:641:in `method_missing'
/Users/harshamv/Sites/nomad/db/migrate/20140618100702_create_database_structure.rb:176:in `down'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:598:in `exec_migration'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:579:in `block (2 levels) in migrate'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:578:in `block in migrate'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:577:in `migrate'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:752:in `migrate'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:992:in `block in execute_migration_in_transaction'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:1040:in `ddl_transaction'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:991:in `execute_migration_in_transaction'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:936:in `run'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/migration.rb:818:in `run'
/Users/harshamv/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/railties/databases.rake:79:in `block (3 levels) in <top (required)>'
/Users/harshamv/.rvm/gems/ruby-2.1.2/bin/ruby_executable_hooks:15:in `eval'
/Users/harshamv/.rvm/gems/ruby-2.1.2/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => db:migrate:down
(See full trace by running task with --trace)
答案 0 :(得分：2)
您不能一次将多个表传递给drop_table方法，而是应该这样做：
def down
drop_table :categories
drop_table :countries
end
请参阅drop_table。