test_res.sql

select to_json(a)
from (

	select d1.*,
	(
	  select to_json(t) from
	  (select * from document d2
	  where type = 'author'
	  and d2.id = (d1.body->>'author_id')::int
	  ) t
	) as author,
	(
	  select to_json(array_agg(t)) from
	  (select d3.*, 
	   (
		  select to_json(t) from
		  (select * from document d4
		  where type = 'author'
		  and d4.id = (d3.body->>'author_id')::int
		  ) t
		) as author
	  
	   from document d3
	   where type = 'comment'
	   and (d3.body->>'article_id')::int = d1.id
	  ) t
	) as comments
	
	from document d1
	where type = 'article'
) a

    
/////
    
{
	"id": 107,
	"type": "article",
	"body": {
		"title": "Test article 1",
		"author_id": 52
	},
	"author": {
		"id": 52,
		"type": "author",
		"body": {
			"name": "John doe 46",
			"email": "[email protected]"
		}
	},
	"comments": [{
		"id": 15949,
		"type": "comment",
		"body": {
			"text": "Test comment 5843",
			"author_id": 95,
			"article_id": 107
		},
		"author": {
			"id": 95,
			"type": "author",
			"body": {
				"name": "John doe 89",
				"email": "[email protected]"
			}
		}
	}, {
		"id": 26407,
		"type": "comment",
		"body": {
			"text": "Test comment 16301",
			"author_id": 17,
			"article_id": 107
		},
		"author": {
			"id": 17,
			"type": "author",
			"body": {
				"name": "John doe 11",
				"email": "[email protected]"
			}
		}
	}, {
		"id": 49655,
		"type": "comment",
		"body": {
			"text": "Test comment 39549",
			"author_id": 57,
			"article_id": 107
		},
		"author": {
			"id": 57,
			"type": "author",
			"body": {
				"name": "John doe 51",
				"email": "[email protected]"
			}
		}
	}, {
		"id": 60344,
		"type": "comment",
		"body": {
			"text": "Test comment 50238",
			"author_id": 41,
			"article_id": 107
		},
		"author": {
			"id": 41,
			"type": "author",
			"body": {
				"name": "John doe 35",
				"email": "[email protected]"
			}
		}
	}, {
		"id": 63287,
		"type": "comment",
		"body": {
			"text": "Test comment 53181",
			"author_id": 72,
			"article_id": 107
		},
		"author": {
			"id": 72,
			"type": "author",
			"body": {
				"name": "John doe 66",
				"email": "[email protected]"
			}
		}
	}, {
		"id": 72609,
		"type": "comment",
		"body": {
			"text": "Test comment 62503",
			"author_id": 57,
			"article_id": 107
		},
		"author": {
			"id": 57,
			"type": "author",
			"body": {
				"name": "John doe 51",
				"email": "[email protected]"
			}
		}
	}, {
		"id": 91950,
		"type": "comment",
		"body": {
			"text": "Test comment 81844",
			"author_id": 14,
			"article_id": 107
		},
		"author": {
			"id": 14,
			"type": "author",
			"body": {
				"name": "John doe 8",
				"email": "[email protected]"
			}
		}
	}, {
		"id": 98428,
		"type": "comment",
		"body": {
			"text": "Test comment 88322",
			"author_id": 10,
			"article_id": 107
		},
		"author": {
			"id": 10,
			"type": "author",
			"body": {
				"name": "John doe 4",
				"email": "[email protected]"
			}
		}
	}, {
		"id": 102108,
		"type": "comment",
		"body": {
			"text": "Test comment 92002",
			"author_id": 92,
			"article_id": 107
		},
		"author": {
			"id": 92,
			"type": "author",
			"body": {
				"name": "John doe 86",
				"email": "[email protected]"
			}
		}
	}]
}