Generate single complex JSON object from PostgreSQL query

Question

I have a PostgreSQL database with the following tables:

Building

ID	NAME	DESCRIPTION
1	Building 1	1st Building Description
2	Building 2	2nd Building Description
3	Building 3	3rd Building Description

Floor

ID	NAME	DESCRIPTION	BUILDING_ID
1	Floor 1.1	Floor Description 1.1	1
2	Floor 1.2	Floor Description 1.2	1
3	Floor 2.1	Floor Description 2.1	2
4	Floor 2.2	Floor Description 2.2	2
5	Floor 3.1	Floor Description 3.1	3

Room

ID	NAME	DESCRIPTION	FLOOR_ID
1	Room 1.1.1	Room Description 1.1.1	1
2	Room 1.1.2	Room Description 1.1.2	1
3	Room 1.2.1	Room Description 1.2.1	2
4	Room 1.2.2	Room Description 1.2.2	2
5	Room 3.1.1	Room Description 2.1.1	5

The code for generating the above structure can be found in this SQL Fiddle , here .

I want to generate a single JSON object with a single query, with the following structure:

{
  "Building 1": {
    "details": {
      "id": 1,
      "name": "Building 1",
      "description": "1st Building Description"
    },
    "floors": {
      "Floor 1.1": {
        "details": {
          "id": 1,
          "name": "Floor 1.1",
          "description": "Floor Description 1.1"
        },
        "rooms": {
          "Room 1.1.1": {
            "id": 1,
            "name": "Room 1.1.1",
            "description": "Room Description 1.1.1"
          },
          "Room 1.1.2": {
            "id": 2,
            "name": "Room 1.1.2",
            "description": "Room Description 1.1.2"
          }
        }
      },
      "Floor 1.2": {
        "details": {
          "id": 2,
          "name": "Floor 1.2",
          "description": "Floor Description 1.2"
        },
        "rooms": {
          "Room 1.2.1": {
            "id": "3",
            "name": "Room 1.2.1",
            "description": "Room Description 1.2.1"
          },
          "Room 1.1.2": {
            "id": 4,
            "name": "Room 1.2.2",
            "description": "Room Description 1.2.2"
          }
        }
      },
    }
  },
  
  
  "Building 2": {
    "details": {
      "id": 2,
      "name": "Building 2",
      "description": "2nd Building Description"
    },
    "floors": {
      "Floor 2.1": {
        "details": {
          "id": 3,
          "name": "Floor 2.1",
          "description": "Floor Description 2.1"
        },
        "rooms": {
        }
      },
      "Floor 2.2": {
        "details": {
          "id": 4,
          "name": "Floor 2.2",
          "description": "Floor Description 2.2"
        },
        "rooms": {
        }
      },
    }
  },
  
    
  
  "Building 3": {
    "details": {
      "id": 3,
      "name": "Building 3",
      "description": "3rd Building Description"
    },
    "floors": {
      "Floor 3.1": {
        "details": {
          "id": 5,
          "name": "Floor 3.1",
          "description": "Floor Description 3.1"
        },
        "rooms": {
          "Room 3.1.1": {
            "id": 5,
            "name": "Room 3.1.1",
            "description": "Room Description 3.1.1"
          }
        }
      }
    }
  },
}

To explain the above structure:

1. A single object output is needed
2. The keys are always represented by the name of the objects
3. All the fields are contained in a details object
4. All the children objects are flattened inside another object in a similar way

Unfortunately, I can only use json_build_object because the above structure cannot be altered since it was already defined.

Thank you!

Answer 1

Her you can have an example of what you can do. You will have to correct and complete this script, but I think it can do the job

select json_build_object(b.name,json_build_object('details',row_to_json(b),
                        'floors',json_build_object('details',(select json_agg(row_to_json(f))->0 from (select * from floors f where f.building_id = b.id) f)))) 
from buildings b