Asked  7 Months ago    Answers:  5   Viewed   166 times

I am using the Ruby on Rails 3.1 pre version. I like to use PostgreSQL, but the problem is installing the pg gem. It gives me the following error:

$ gem install pg
Building native extensions.  This could take a while...
ERROR:  Error installing pg:
    ERROR: Failed to build gem native extension.

        /home/u/.rvm/rubies/ruby-1.9.2-p0/bin/ruby extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
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:

Gem files will remain installed in /home/u/.rvm/gems/ruby-1.9.2-p0/gems/pg-0.11.0 for inspection.
Results logged to /home/u/.rvm/gems/ruby-1.9.2-p0/gems/pg-0.11.0/ext/gem_make.out

How do I solve this problem?



It looks like in Ubuntu that header is part of the libpq-dev package (at least in the following Ubuntu versions: 11.04 (Natty Narwhal), 10.04 (Lucid Lynx), 11.10 (Oneiric Ocelot), 12.04 (Precise Pangolin), 14.04 (Trusty Tahr) and 18.04 (Bionic Beaver)):


So try installing libpq-dev or its equivalent for your OS:

  • For Ubuntu/Debian systems: sudo apt-get install libpq-dev
  • On Red Hat Linux (RHEL) systems: yum install postgresql-devel
  • For Mac Homebrew: brew install postgresql
  • For Mac MacPorts PostgreSQL: gem install pg -- --with-pg-config=/opt/local/lib/postgresql[version number]/bin/pg_config
  • For OpenSuse: zypper in postgresql-devel
  • For ArchLinux: pacman -S postgresql-libs
Tuesday, June 1, 2021
answered 7 Months ago

You should run following command to install NodeJS in Ubuntu

sudo apt-get install nodejs

or run this for OSX

brew install nodejs

Uglifier is a JS wrapper and it needs a JS runtime running or JS interpreter. I would choose to install NodeJS.

Monday, June 21, 2021
answered 6 Months ago

From Arel documentation

The OR operator is not yet supported. It will work like this: users.where(users[:name].eq('bob').or(users[:age].lt(25)))

This RailsCast shows you how to use the .or operator. However, it works with Arel objects while you have instances of ActiveRecord::Relation. You can convert a relation to Arel using Product.name_a.arel, but now you have to figure out how to merge the conditions.

Thursday, July 29, 2021
answered 5 Months ago

Using homebrew fixed this for me:

gem uninstall pg
brew install apple-gcc42
gem install pg

EDIT: I also manually installed "devtools"

xcode-select --install
Sunday, August 1, 2021
answered 4 Months ago

For an array, you can use one of these:

# Will raise exception if any value not found
User.find( [1,3,5] )

# Will not raise an exception
User.find_all_by_id( [1,3,5] ) # Rails 3
User.where(id: [1,3,5])        # Rails 4

If you happen to be using a range, you can use these:

# Will raise exception if any value not found
User.find((1..4).to_a)   #same as User.find([1,2,3,4])

# Will not raise an exception
User.find_all_by_id(1..4)  # Rails 3
User.where(id: 1..4)       # Rails 4

As @diego.greyrobot notes in a comment, a range causes a SQL BETWEEN clause, whereas an array causes a SQL IN clause.

Don't use User.find_by_id() -- It will only return one record, no matter how may IDs you pass in.

Sunday, August 8, 2021
answered 4 Months ago
Only authorized users can answer the question. Please sign in first, or register a free account.
Not the answer you're looking for? Browse other questions tagged :