Added export script and documentation.

Author: sun

README.md

@@ -0,0 +1,62 @@
+# Google Firebase Firestore JSON Export
+
+Exports a Google Firestore database recursively including all collections and
+subcollections into plain JSON files.
+
+Uses the built-in `recursive()` flag of the Query class:
+https://cloud.google.com/python/docs/reference/firestore/latest/query#recursive
+
+Allows you to analyze the data in your Firestore database locally without being
+constrained to Firestore or BigQuery limitations.  For example:
+
+- Finding incomplete documents
+- Finding broken document references
+- Finding documents without fields
+- Querying subcollections of collections without documents
+
+You can use custom scripts or the powerful [jq command-line JSON processor](https://jqlang.github.io/jq/)
+to perform complex lookups, such as [this example](https://unix.stackexchange.com/a/466241/228730),
+or the following, which extracts all documents that do not have the key `'createdBy'`:
+
+```console
+jq -r 'with_entries(select(.value.createdBy == null))' collection.json
+```
+
+
+:warning: **Warning**: A complete export causes 1 read operation for every document in
+your Firestore database.  Depending on the size of your database, this might
+induce costs for database reads.
+
+
+## Requirements
+
+- Python 3
+
+
+## Setup and Usage
+
+1. Install firebase-admin via pip
+    ```console
+    $ pip3 install firebase-admin
+    ```
+
+2. Run export to JSON.
+    ```console
+    $ python3 main.py
+    ```
+
+
+## Todos
+
+- Serialize TimestampWithNanoseconds (instead of converting to string)
+  https://code.luasoftware.com/tutorials/google-cloud-firestore/python-firestore-query-documents-to-json
+
+- Serialize document references (e.g. as document path instead of address)
+  ```
+  "ref": "<google.cloud.firestore_v1.document.DocumentReference object at 0x111ef1c50>"
+  ```
+
+- Import into local Firestore emulator
+
+- Allow to export as line-delimited JSON (LDJSON) to allow streaming and avoid
+  loading the whole db into memory when importing.

main.py

@@ -0,0 +1,42 @@
+import firebase_admin
+from firebase_admin import credentials
+from firebase_admin import firestore
+import json
+
+key_file = "../credentials.json"
+cred = credentials.Certificate(key_file)
+firebase_admin.initialize_app(cred)
+
+db = firestore.client()
+
+# @thanks https://stackoverflow.com/a/57561744/811306
+def set(my_dict, field_path, value):
+    """Given `foo`, 'key1.key2.key3', 'something', set foo['key1']['key2']['key3'] = 'something'"""
+    here = my_dict
+    keys = field_path.split('.')
+    for key in keys[:-1]:
+        # Create key with empty dictionary if it does not exist and move pointer.
+        here = here.setdefault(key, {})
+    here[keys[-1]] = value
+
+# for collection in [{id: 'dayplans'}]:
+for collection in db.collections():
+    collection_name = collection.id
+    print(f"Exporting {collection_name}...")
+    json_file = collection_name + '.json'
+
+    # documents = db.collection(collection_name).recursive().limit(100).get()
+    documents = db.collection(collection_name).recursive().get()
+    data = {}
+    for doc in documents:
+        print(doc.reference.path)
+        keys = doc.reference.path.split('/')[1:]
+        key = '.'.join(keys)
+        set(data, key, doc.to_dict())
+
+    # print(json.dumps(data, indent=2, default=str))
+
+    with open(json_file, 'w') as file:
+        json.dump(data, file, indent=4, sort_keys=True, default=str, ensure_ascii=False)
+
+    print(f"☑️  Exported to {json_file}.")