Rails 5，为 Postgres 9.5.4 安装 pg gem 时出错

Question

使用 PostgreSQL 9.5.4 开发新的 Ruby on Rails 5.0 应用程序。尝试安装 pg gem 时遇到问题

捆绑安装失败，因为它似乎无法找到 pg_config 并且在尝试构建本机扩展时出错。

ERROR:  Error installing pg:
ERROR: Failed to build gem native extension.

checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
--with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no

Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/Users/brian.hooper/.rbenv/versions/2.3.0/bin/$(RUBY_BASE_NAME)
    --with-pg
    --without-pg
    --enable-windows-cross
    --disable-windows-cross
    --with-pg-config
    --without-pg-config
    --with-pg_config
    --without-pg_config
    --with-pg-dir
    --without-pg-dir
    --with-pg-include
    --without-pg-include=${pg-dir}/include
    --with-pg-lib
    --without-pg-lib=${pg-dir}/lib

To see why this extension failed to compile, please check the mkmf.log

Answer 1

经过一些故障排除后，这是我用来解决此问题的简单方法：

1.) 在您的 postgresql 安装目录的 bin 目录下找到 pg_config

# Example: 
/Library/PostgreSQL/9.5/bin/pg_config

2.) 从 Rails 项目的根目录运行以下捆绑命令

bundle config build.pg --with-pg-config=<path_to_postgresql>/bin/pg_config

# Example:
bundle config build.pg --with-pg-config=/Library/PostgreSQL/9.5/bin/pg_config

3.) 构建完成后，运行bundle install。正如您在下面看到的那样，pg gem 已成功安装。 Installing pg 0.18.4 with native extensions

bundle install

Fetching gem metadata from https://rubygems.org/...........
Fetching version metadata from https://rubygems.org/...
Fetching dependency metadata from https://rubygems.org/..
Resolving dependencies.....
Using rake 11.2.2
Using concurrent-ruby 1.0.2
Using i18n 0.7.0
Using minitest 5.9.0
Using thread_safe 0.3.5
Using builder 3.2.2
Using erubis 2.7.0
Using mini_portile2 2.1.0
Using pkg-config 1.1.7
Using rack 2.0.1
Using nio4r 1.2.1
Using websocket-extensions 0.1.2
Using mime-types-data 3.2016.0521
Using arel 7.1.1
Using bundler 1.11.2
Using byebug 9.0.5
Using coffee-script-source 1.10.0
Using execjs 2.7.0
Using method_source 0.8.2
Using thor 0.19.1
Using debug_inspector 0.0.2
Using ffi 1.9.14
Using multi_json 1.12.1
Using rb-fsevent 0.9.7
Installing pg 0.18.4 with native extensions
Using puma 3.6.0
Using sass 3.4.22
Using tilt 2.0.5
Using spring 1.7.2
Using turbolinks-source 5.0.0
Using tzinfo 1.2.2
Using nokogiri 1.6.8
Using rack-test 0.6.3
Using sprockets 3.7.0
Using websocket-driver 0.6.4
Using mime-types 3.1 
Using coffee-script 2.4.1
Using uglifier 3.0.1
Using rb-inotify 0.9.7
Using turbolinks 5.0.1
Using activesupport 5.0.0.1
Using loofah 2.0.3
Using mail 2.6.4
Using listen 3.0.8
Using rails-dom-testing 2.0.1
Using globalid 0.3.7
Using activemodel 5.0.0.1
Using jbuilder 2.6.0
Using rails-html-sanitizer 1.0.3
Using spring-watcher-listen 2.0.0
Using activejob 5.0.0.1
Using activerecord 5.0.0.1
Using actionview 5.0.0.1
Using actionpack 5.0.0.1
Using actioncable 5.0.0.1
Using actionmailer 5.0.0.1
Using railties 5.0.0.1
Using sprockets-rails 3.1.1
Using coffee-rails 4.2.1
Using jquery-rails 4.1.1
Using web-console 3.3.1
Using rails 5.0.0.1
Using sass-rails 5.0.6
Bundle complete! 15 Gemfile dependencies, 63 gems now installed.
Use `bundle show [gemname]` to see where a bundled gem is installed.