Creates 2 Notion Databases, where the second has a Relation and Roll Ups to the first.

create-notion-database-with-relation.py

import json
import os

from dotenv import load_dotenv
import requests

class NotionClient():
    def __init__(self, notion_key):
        self.notion_key = notion_key
        self.default_headers = {'Authorization': f"Bearer {self.notion_key}",
                                'Content-Type': 'application/json', 'Notion-Version': '2022-06-28'}
        self.session = requests.Session()
        self.session.headers.update(self.default_headers)    

    def create_database(self, data):
        url = "https://api.notion.com/v1/databases"
        response = self.session.post(url, json=data)
        return response.json()

def main(page_id):
    notion_client = NotionClient(os.getenv('NOTION_KEY'))
    print(f"*** Creating database under {page_id} ***")

    minimum = {
        "parent": {
            "type": "page_id",
            "page_id": page_id
        },
        "properties": {
            "Name": {
                "title": {}
            }
        }
    }

    basic_create_response = notion_client.create_database(minimum)
    print(json.dumps(basic_create_response, indent=2))

    catches = {
        "parent": {
            "type": "page_id",
            "page_id": page_id
        },
        "icon": {
            "type": "emoji",
                "emoji": "🐟"
        },
        "title": [
            {
                "type": "text",
                "text": {
                    "content": "Catches",
                    "link": None
                }
            }
        ],
        "properties": {
            "Name": {
                "title": {}
            },
            "Weight (lbs)": {
                "number": {}
            },
            "Location": {
                "rich_text": {}
            },
            "Date": {
                "date": {}
            },    
            "Species": {
                "select": {
                    "options": [
                        {
                            "name": "Northern Pike",
                            "color": "green"
                        },
                        {
                            "name": "Walleye",
                            "color": "red"
                        },
                        {
                            "name": "Smallmouth Bass",
                            "color": "pink"
                        }
                    ]
                }
            }       
        }
    }

    print("*** Creating catches database ***")
    catches_create_response = notion_client.create_database(catches)
    print(json.dumps(catches_create_response, indent=2))

    trips = {
        "parent": {
            "type": "page_id",
            "page_id": page_id
        },
        "title": [
            {
                "type": "text",
                "text": {
                    "content": "Trips",
                    "link": None
                }
            }
        ],
        "cover": {
            "type": "external",
            "external": {
                "url": "https://images.unsplash.com/photo-1597956959732-9b8cb12f8960?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=1332&q=80"
            }
        },
        "properties": {
            "Trip Name": {
                "title": {}
            },
            "Catches": {
                "relation": {
                    "database_id": catches_create_response.get("id"),
                    "type": "dual_property",
                    "dual_property": {}
                }
            },
            "Total Weight Caught": {
                "rollup": {
                    "rollup_property_name": "Weight (lbs)",
                    "relation_property_name": "Catches",
                    "function": "sum"
                }
            },
            "Total Fish Caught": {
                "rollup": {
                    "rollup_property_name": "Name",
                    "relation_property_name": "Catches",
                    "function": "count_values"
                }
            }  
        }
    }

    print("*** Creating Trips Database ***")
    trips_create_response = notion_client.create_database(trips)
    print(json.dumps(trips_create_response, indent=2))

if __name__ == "__main__":
    import argparse
    load_dotenv(override=True)
    parser = argparse.ArgumentParser(description='Create a Notion Database.')
    parser.add_argument('page_id', type=str,
                        help='A Notion Page ID to create the database under')

    args = parser.parse_args()

    main(args.page_id)