title: Add multiple tinyDB databases together
body: <p>How do I add multiple tinyDB (document based database) databases together without getting a <code>AssertionError</code> error?
  I'm trying to add in this example 12 tinyDB databases together.</p>
  <p>File structure:<br>
  <a href="https://i.stack.imgur.com/Eq1FP.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Eq1FP.png" alt="enter image description here" /></a></p>
  <p>Every numbered file looks likes this:<br></p>
  <pre class="lang-json prettyprint-override"><code>{
      &quot;_default&quot;: {
          &quot;1&quot;: {
              &quot;Strategy&quot;: &quot;MAShift&quot;,
              &quot;Symbol&quot;: &quot;AAVE/USD&quot;,
              &quot;Timeframes&quot;: [
                  &quot;30T&quot;
              ],
              &quot;Parameters&quot;: {
                  &quot;atr&quot;: 14,
                  &quot;sma&quot;: 5,
                  &quot;longLine&quot;: 3,
                  &quot;shortLine&quot;: 5,
                  &quot;slMultipier&quot;: 12,
                  &quot;leverage&quot;: 1
              },
              &quot;Start&quot;: &quot;2020-10-13 12:00:00&quot;,
              &quot;End&quot;: &quot;2021-04-26 11:30:00&quot;,
              &quot;Duration (days)&quot;: 194,
              &quot;Equity Start [$]&quot;: 10000,
              &quot;Equity Final [$]&quot;: 90470.5732,
              &quot;Return [%]&quot;: 804.71,
              &quot;Max. Drawdown [%]&quot;: -28.1,
              &quot;Win rate [%]&quot;: 69.12,
              &quot;Total trades&quot;: 570,
              &quot;Avg. trade [%]&quot;: 0.43,
              &quot;Avg. winning trade [%]&quot;: 1.88,
              &quot;Avg. losing trade [%]&quot;: -2.81
          }, ...
      }
  }
  </code></pre>
  <p>My code:</p>
  <pre class="lang-py prettyprint-override"><code>from tinydb import TinyDB
  
  resultsTotalDb = TinyDB(f'db/backtestingResultsTotal.json')
  
  for i in range(12):
      resultsDb = TinyDB(f'db/backtestingResults{i}.json')
      for result in resultsDb.all():
          resultsTotalDb.insert(result)
  </code></pre>
  <p>Error:</p>
  <p><code>AssertionError: doc_id 1 already exists</code></p>