title: MongoDB - Find and return all the items of an array in each document
body: <p>so I have this system where users can input tags, but i want to add suggestions/auto-complete with dynamic data from all the previous tags in the database. </p>
  
  <p>Here's what the data looks like: </p>
  
  <pre><code>    collection = [
        {
          title: "Avengers",
          tags:["si-fi", "powers", "super-heroes", "iron-man"],
          ...
        },
        {
          title: "Lego Movie"
          tags:["spider-man", "bottle", "man of steel"],
          ...
        }
        ...
      ]
  </code></pre>
  
  <p>So I want to retreive an array of all the tags that match a search string.</p>
  
  <p>For example, if I search with <code>'man'</code>, I want the data returned to be:</p>
  
  <pre><code>[
    "iron-man",
    "spider-man",
    "man of steel"
  ]
  </code></pre>