title: Check if user exists in room databse through id
body: <p>I want to keep the app scanning for qr codes if it doesnt match the userId..</p>
  <p>So my question is, how can I check if a user already exists in my room db?</p>
  <pre><code> @Query(&quot;select * from user_table where id= :id&quot;)
      fun getUserById(id: Int) : User
  </code></pre>
  <p>I previously tried this, because I could need the user object in return by the function.
  But it only return a Kotlin.Unit</p>
  <pre><code> val currentuser = mUserViewModel.getUserById(sId)
  </code></pre>