title: Mongo db In Query with limit for each record
body: <p>I have an array of id's authorIds=["1","2",3","4"]. I have another array that holds the reference to the authorIds.
  ex:</p>
  
  <pre><code>book=[
  {
        bookId:"abcd",
        authorId:"1"
  },
  {
        bookId:"def",
        authorId:"1"
  }
  {
        bookId:"ghi",
        authorId:"2"
  }
  {
        bookId:"kjl",
        authorId:"1"
  }
  ];
  </code></pre>
  
  <p>now i would like to use the In query (mongodb C# drvier) but want to restrict the number of books to 5 for each author. Can someone tell me how to do this.</p>