How to use not_if in a chef recipe

I had been having the same issue. But, in my case, "not_if" seems executed by different user (root), and failed to check the condition properly. Adding [:user => "postgres"] resolved the issue.

execute "create-database-user" do    user "postgres"    exists = <<-EOH    psql -U postgres -c "select * from pg_user where usename='#{settings[:username]}'" | grep -c #{settings[:username]}    EOH    command "createuser -U postgres -sw #{settings[:username]}"    not_if exists, :user => "postgres"end

I've referred the following code example.

https://github.com/MarcinKoziuk/chef-postgres-dbsetup/blob/master/recipes/default.rb

You're checking for the existence of:

node[:user]

If it doesn't exist, you create:

node[:postgresql][:user]

Unless these happen to be equal, you'll keep trying to create node[:postgresql][:user] repeatedly.

First, there is a typo in the WHERE condition. It should probably be username instead of usename.

Anyawy, you should do:

execute "create-user" do    user "postgres"    command "createuser -s #{node[:user]}"    not_if "psql -U postgres -c \"select * from pg_user where username='#{node[:user]}'\" | grep -c #{node[:user]}"end

This assumes that your psql -U postgres -c "select * from pg_user where username='#{node[:user]}'" is correct.

Same with a database:

execute "create-database" douser "postgres"command "createdb #{node[:database]}"not_if "psql -U postgres -c \"select * from pg_database WHERE datname='#{node[:database]}'\" | grep -c #{node[:database]}}"end

Regarding the username, even if it already exists, changing the password to the known one shouldn't cause a problem. After all you know the password.

FYI, you can define multiple conditionals within one resource.

Good luck with Chef! I love it very much!