title: How to make field in document unique?
body: <p>I am using spring data mongo. There is a field in <code>document</code> apart from <code>primary key</code> which needs to be unique but as per my requirement I can't use <code>@Indexed(unique=true)</code>. Is there any annotation like <code>@Column(unique=true)</code> in spring data mongo to make the field as a unique?</p>