title: Why won't my ASP.Net Core Web API Controller return XML?
body: <p>I have the following simple Web API controller:</p>
  <pre><code>    // GET: api/customers
      [HttpGet]
      public async Task&lt;IActionResult&gt; Get()
          {
          var customers = await uow.Users.GetAllAsync();
          var dto = customers.Select(p =&gt; new CustomerDto {Id = p.Id, Email = p.Email, UserName = p.UserName});
          return Ok(dto); // IEnumerable&lt;CustomerDto&gt;
          }
  </code></pre>
  <p>In Postman, I'm setting the Accept header to <code>application/xml</code>, but no matter what I try, I can only get JSON data back.</p>
  <p><a href="https://i.stack.imgur.com/D3Sjt.png" rel="noreferrer"><img src="https://i.stack.imgur.com/D3Sjt.png" alt="Postman screen shot" /></a></p>
  <p>I read somewhere that in order to get XML, I must add <code>[DataContract]</code> and <code>[DataMember]</code> attributes to my DTO, which now looks like this:</p>
  <pre><code>[DataContract]
  public class CustomerDto
      {
      [DataMember]
      public string Id { get; set; }
  
      [Required]
      [EmailAddress]
      [Display(Name = &quot;Email&quot;)]
      [DataMember]
      public string Email { get; set; }
  
      [Required]
      [Display(Name = &quot;Login Name&quot;)]
      [DataMember]
      public string UserName { get; set; }
      }
  </code></pre>
  <p>I've been at it several hours now and I'm just not seeing why it doesn't work. I've tried:</p>
  <ul>
  <li><p>Making the action method synchronous and asynchronous</p>
  </li>
  <li><p>Returning the data directly, and setting the return type to <code>IEnumerable&lt;CustomerDto&gt;</code></p>
  </li>
  <li><p>Converting the collection to an array instead of a list</p>
  </li>
  <li><p>Returning an <code>IActionResult</code></p>
  </li>
  <li><p>Returning a single item, instead of a collection</p>
  </li>
  <li><p>I've verified that the Accept header is showing up in the request by examining it in the debugger.</p>
  </li>
  <li><p>Lots of &quot;Googling with Bing&quot; and reading various blogs</p>
  </li>
  <li><p>Creating a new WebAPI project from the template and seeing if there is any inspiration there (not really).</p>
  <p>I expect it's simple, but I can't see it...</p>
  </li>
  </ul>