title: The instance of entity type 'Product' cannot be tracked because another instance with the same key value is already being tracked
body: <p>I made a test with code below to update the <code>Product</code>:</p>
  
  <pre><code>var existing = await _productRepository.FirstOrDefaultAsync(c =&gt; c.Id == input.Id);
  if (existing == null)
      throw new UserFriendlyException(L("ProductNotExist"));
  var updatedEntity = ObjectMapper.Map&lt;Product&gt;(input);
  var entity = await _productRepository.UpdateAsync(updatedEntity);
  </code></pre>
  
  <p>But it throws an exception:</p>
  
  <blockquote>
    <p>Mvc.ExceptionHandling.AbpExceptionFilter - The instance of entity type 'Product' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.</p>
  </blockquote>
  
  <p>This is caused by querying <code>existing</code>. Is there any solution for this?</p>