title: How to set multiple fields as uniqueKey in solr?
body: <p>I have these fields in my solr schema :</p>
  
  <pre><code>&lt;fields&gt;
      &lt;field name="Id" type="string" indexed="true" stored="true" multiValued="false" required="true" /&gt;
      &lt;field name="IdCategory" type="string" indexed="true" stored="true" multiValued="false" required="true" /&gt;
      &lt;field name="Rank" type="long" indexed="true" stored="true" multiValued="false" required="true" /&gt;
      &lt;field name="TypeRank" type="string" indexed="true" stored="true" multiValued="false" required="false" default="category" /&gt;
  
      &lt;field name="_version_" type="long" indexed="true" stored="true"/&gt;
  &lt;/fields&gt;
  </code></pre>
  
  <p>Can i use 2 or 3 fields as uniqueKeys instead of One?
  When I try :</p>
  
  <pre><code>&lt;uniqueKey&gt;(Id,IdCategory,Rank,TypeRank)&lt;/uniqueKey&gt;
  </code></pre>
  
  <p>I get the following error :</p>
  
  <blockquote>
    <p>org.apache.solr.common.SolrException:org.apache.solr.common.SolrException: Schema Parsing Failed: unknown field '(Id,IdCategory,Rank,TypeRank)'. Schema file is /var/solr/Rank/schema.xml </p>
  </blockquote>