join in loopback 4 code example

Example 1: loopback relations include inside include

// Return all post owners (users), and all posts and orders of
// each owner. The posts also include images.
Post.find({include: {owner: [{posts: 'images'} , 'orders']}}, 
          function() { /* ... */ });

Example 2: loopback include relation

in url:
/customers?filter[include]=reviews

in code:
User.find({include: 'reviews'}, function() { /* ... */ });