title: React-Admin "Get List" DataProvider
body: <p>I'm starting to use the <code>react-admin</code> package.<br/> I am blocked in my development because I would like to make a <code>Select</code> with the data of another <code>Resource</code>. And that's why I use <code>ReferenceField</code> but I don't know why I get this error when I use this element.</p>
  
  <pre class="lang-js prettyprint-override"><code>Error: The response to 'GET_LIST' must be like { data : [{ id: 123, ...}, ...] }, but at least one received data item do not have an 'id' key. The dataProvider is probably wrong for 'GET_LIST
  </code></pre>
  
  <p>Here is the data that I receive from my API:</p>
  
  <pre class="lang-js prettyprint-override"><code>[{"_id":"5e3ec3baa6480d002b24ea90","name_promo":"test","years":"2019-01-01T00:00:00.000Z","__v":0}]
  </code></pre>
  
  <p>For information, I use the Provider <code>ra-data-json-server</code></p>
  
  <p>Here is my code:</p>
  
  <pre class="lang-js prettyprint-override"><code>import React from 'react';
  import {
      Create,
      SimpleForm,
      TextInput,
      ReferenceInput,
      SelectInput,
  } from 'react-admin';
  
  const CreateUser = (props) =&gt; (
      &lt;Create {...props}&gt;
          &lt;SimpleForm&gt;
              &lt;TextInput source="lastName" label="Prénom" /&gt;
              &lt;TextInput source="firstName" label="Nom" /&gt;
              &lt;TextInput source="email" label="Email" /&gt;
              &lt;TextInput source="role" label="Role" /&gt;
              &lt;ReferenceInput  label="Session" source="id" reference="sessions"  &gt;
                  &lt;SelectInput optionText="name_promo"/&gt;
              &lt;/ReferenceInput &gt;
          &lt;/SimpleForm&gt;
      &lt;/Create&gt;
  );
  
  export default CreateUser;
  </code></pre>