[RUBY] Resolve ActiveRecord :: NoDatabaseError on rails6

The hardware uses MacBook Air, and the development environment uses VScode.

This is a solution for the error that accompanies the previous article (Making the database PostgreSQL with rails new) (https://qiita.com/satomomo0222/items/e77e200ec6e526076764).

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Specify PostgreSQL as database

$ rails _5.1.6_new app name--database=postgresql

Do this in rails 6

$ rails server

When you start the server with and access [localhost: 3000](http: // localhost: 3000 /), I get the error ** ActiveRecord :: NoDatabaseError **.

This is an error caused by the ** database not existing. ** **

Solution: Create a database

How to do it automatically

First, change to the directory created by rails new.

$cd created directory

next

$ rails db:create

To generate the database. The database will be automatically generated according to the contents of config / database.yml.

How to do it manually

First, change to the directory created by rails new.

$cd created directory

 > Next, rewrite config / database.yml.

>```:config/database.before changing yml
~abridgement~

>development:
  <<: *default
  database:app name_development

>~abridgement~

~abridgement~

development: <<: *default database:app name_db host: localhost encoding: utf8 reconnect: false username:My username

~abridgement~

 > * Since database: is the database name, change development to db for easy understanding.
 Others (hots, encoding, recconect, username) can be solved without adding them, but it is recommended to add them.


 > ** Next, launch SQL. ** **

>```
$ psql -h localhost -p 5432 -U your username-d postgres

>psql (12.3)
Type "help" for help.

>postgres=# 

About commands around here https://www.postgresql.jp/document/9.3/html/app-psql.html It is described in detail in.

($ psql -h localhost -d postgres ← This alone solved the problem.)

Run this command and you will be able to enter SQL statements. I will write the SQL statement to create the database here.

postgres=#

#### **`After input`**
```python

postgres=#create database app name_db;

Here, ** app name \ _db is the database: app name \ _db specified in config / database.yml first. ** **

postgres=#create database app name_db; CREATE DATABASE postgres=# \q

 You can exit by typing \ q at the end.

 Now start the server again with $ rails server and try accessing localhost: 3000. The error should have been resolved.

# I solved it safely!
 If you find it useful, I would be grateful if you could click the ** LGTM button. ** **
 Let's do our best to learn Rails together! : raised_hand_tone1: