Ansible: How check when: db is present in role variable?

Question

So I am trying to understand how to pass role variables in playbooks and I stumbled upon the syntax a bit. I can´t figure out how tell ansible to only create a mysql DB if it does not exist. It is specifically passing it as a role variable that I find challenging. Can it be passed a state=present?

Here is my code:

---
- name: Install MySQL
  host: development
  roles:
   - {role: mysql, mysql_db: [{name: benz}], when: ????,
        mysql_users: [{name: ben3, pass: foobar, priv: "*.*:ALL"}], when: ???}

Answer 1

I don't believe roles is the best way to approach the problem because you can't register variables before a role statement gets evaluated. From the documentation you can only use ansible facts that actually get evaluated before your playbook executes. Another comment, the when keyword is meant to be used only once in the role statement:

---
- name: Install MySQL
  host: development
  roles:
   - {role: mysql,
      mysql_db: [{name: benz}],
      mysql_users: [{name: ben3, pass: foobar, priv: "*.*:ALL"}],
      when: "some_ansible_fact == 'Whatever'"}

You are probably better off putting your checks in playbook tasks if you need to check whether a mysql database exists or not. you can use the register keyword to see if a database exists:

---
- name: Install Mysql
  hosts: all
  user: myrootuser
  sudo: True
  tags: mytag

  vars:
      mysql_users: [{name: ben3, pass: foobar, priv: "*.*:ALL"}]
      mysql_db: mydatabasename

  tasks:

    - name: Install the mysql package
      apt: pkg=mysql-server state=present

    - name: Find out the master log file name and position
      command: >
        /usr/bin/mysql -umysql_user -pmysql_password
        -e "SHOW DATABASES;"
      register: databases

    - name: Create users if they don't exist
      command: >
        # or run whatever you need to run here to create users
        /usr/bin/mysql -umysql_user -pmysql_password
        -e "CREATE USER {{ mysql_users[0]['name'] }};"
      when: databases.stdout.find('{{ mysql_db }}') != -1

Hope this helps.