在rails中保存对象后出现错误

ActiveRecord::RecordNotUnique: duplicate key value violates unique constraint "users_email_key"

user = User.find_or_create_by(email: params[:email])

ActiveRecord::RecordInvalid: Validation failed: Name is too short (minimum is 3 characters)

class User < ApplicationRecord
  validates :name, length: { minimum: 3 }
end

# 控制器中
def create
  @user = User.new(user_params)
  if @user.save
    redirect_to @user, notice: 'User was successfully created.'
  else
    render :new
  end
end

ActiveRecord::StatementInvalid: PG::TransactionRollbackError: could not serialize access due to concurrent update

ActiveRecord::Base.transaction do
  @user = User.find(params[:id])
  @user.update!(attribute: value)
end

ActiveRecord::ConnectionNotEstablished: could not connect to server: Connection refused

# database.yml
default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: myapp_development

ActiveRecord::NoPermissionsError: You don't have permission to access this table

GRANT ALL PRIVILEGES ON myapp_development TO myapp_user;