Fetching mysql2 0.5.2
Installing mysql2 0.5.2 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
(中略)
An error occurred while installing mysql2 (0.5.2), and Bundler cannot
continue.
Make sure that `gem install mysql2 -v '0.5.2' --source 'https://rubygems.org/'`
succeeds before bundling.
In Gemfile:
mysql2
run bundle exec spring binstub --all
Could not find gem 'mysql2 (>= 0.4.4, < 0.6.0)' in any of the gem sources listed in your Gemfile.
Run `bundle install` to install missing gems.
app_development=# \dt
List of relations
Schema | Name | Type | Owner
--------+----------------------+-------+----------
public | ar_internal_metadata | table | postgres
public | schema_migrations | table | postgres
(2 rows)
マイグレーションを実行する
users テーブルが無い状態でマイグレーションしてみます。
$ bin/rails db:migrate
psql で確認するとテーブルが作られていることがわかります。
app_development=# \dt
List of relations
Schema | Name | Type | Owner
--------+----------------------+-------+----------
public | ar_internal_metadata | table | postgres
public | schema_migrations | table | postgres
public | users | table | postgres
(3 rows)
カラムの情報を確認すると id カラムも存在しており、 migration によって作られたことがわかります。
app_development=# \d users;
Table "public.users"
Column | Type | Collation | Nullable | Default
--------+-------------------+-----------+----------+-----------------------------------
id | bigint | | not null | nextval('users_id_seq'::regclass)
name | character varying | | |
Indexes:
"users_pkey" PRIMARY KEY, btree (id)
テーブルを削除してからロールバックする
psql で users テーブルを削除します。
app_development=# drop table users
ロールバックするとエラーが発生します。
$ bin/rails db:rollback
== 20190713221959 CreateUser: reverting =======================================-- drop_table(:users, {:if_not_exists=>true})
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:
PG::UndefinedTable: ERROR: table "users" does not exist
An error occurred while installing mysql2 (0.5.2), and Bundler cannot continue. Make sure that `gem install mysql2 -v '0.5.2' --source 'https://rubygems.org/'` succeeds before bundling.と出てきたときの対処法
//省略
An error occurred while installing mysql2 (0.5.2), and Bundler
cannot continue.
Make sure that `gem install mysql2 -v '0.5.2' --source
'https://rubygems.org/'` succeeds before bundling.
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
current directory: 省略
checking if the C compiler accepts ... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using system libraries.
Using pkg-config gem version 1.1.9
checking for libxml-2.0... no
checking for libxslt... no
checking for libexslt... no
ERROR: cannot discover where libxml2 is located on your system. please make sure `pkg-config` is installed.
*** extconf.rb failed ***
【注意】javascriptより上に書くこと
