title: Spring Mongo aggregation query with concatenating two arrays and project the result
body: <p>I have a MongoDB aggregation query, I need the Spring boot mongo aggregation object example for the Following query.</p>
  
  <pre><code>db.case.aggregate([ 
    { $project: { item: { $concatArrays: [ "$workApproval.partItems", "$warrantyClaims.items.items" ] } } }
    ,{ $unwind : "$item"} 
  ])  
  </code></pre>
  
  <p>I am stuck on the concatArray portion, I am not sure how to write the above query in Spring Boot Mongo aggregation, any help is appreciated.</p>