diff --git a/.env.local b/.env.local
deleted file mode 100644
index eb624cf..0000000
--- a/.env.local
+++ /dev/null
@@ -1,6 +0,0 @@
-bot_token=
-firebase_apiKey=
-firebase_authDomain=
-firebase_databaseURL=
-firebase_projectId=
-firebase_storageBucket=
diff --git a/.gitignore b/.gitignore
old mode 100644
new mode 100755
index b6e4761..08d0bd2
--- a/.gitignore
+++ b/.gitignore
@@ -102,6 +102,8 @@ celerybeat.pid
 *.sage.py
 
 # Environments
+app.env
+database.env
 .env
 .venv
 env/
diff --git a/Dockerfile b/Dockerfile
new file mode 100755
index 0000000..86cff90
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,7 @@
+FROM python:3.8-buster
+
+WORKDIR /src
+
+COPY ./src/requirements.txt /src
+RUN pip install -r ./requirements.txt
+
diff --git a/LICENSE b/LICENSE
old mode 100644
new mode 100755
diff --git a/Procfile b/Procfile
deleted file mode 100644
index fe54d30..0000000
--- a/Procfile
+++ /dev/null
@@ -1 +0,0 @@
-web: python entrypoint.py
diff --git a/README.md b/README.md
old mode 100644
new mode 100755
index a4ecb9b..f578ee3
--- a/README.md
+++ b/README.md
@@ -26,14 +26,28 @@ python entrypoint.py
 - `python` with version specified in `runtime.txt`
 - `pip` with version `20.0.2`
 
-#### Env file
+#### Env files
+First, copy env files for database and app containers
 ```bash
-cp .env.local .env
+cp docker/config/app/app.dist.env docker/config/app/app.env
+cp docker/config/database/database.dist.env docker/config/app/app.env
 ```
-and then fulfill copied `.env` file with required values
-- `bot_token` - your telegram bot token from [BotFather](https://telegram.me/BotFather)
-- `firebase_*`  - all of those values you can find in firebase console
+and then fulfill copied `.env` files with required values
 
+app.env
+- `bot_token` - your telegram bot token from [BotFather](https://telegram.me/BotFather)
+- `MONGODB_DATABASE` - MongoDB database name
+- `MONGODB_USERNAME` - MongoDB username
+- `MONGODB_PASSWORD` - MongoDB password
+- `MONGODB_HOSTNAME` - MongoDB host (default `database` - container name)
+- `MONGODB_PORT` - MongoDB port (default `port` - given in docker-compose configuration)
+
+database.env
+- `MONGO_INITDB_ROOT_USERNAME` - conf from `app.env`
+- `MONGO_INITDB_ROOT_PASSWORD` - conf from `app.env`
+- `MONGO_INITDB_DATABASE` - conf from `app.env`
+- `MONGODB_DATA_DIR` - directory to store MongoDB documents (inside a container)
+- `MONDODB_LOG_DIR` - log file 
 ### Commands
 #### `/in`
 Will sign you in for everyone-mentions.
@@ -56,7 +70,7 @@ If you haven't opted-in before, alternative reply will be displayed.
 #### `/everone`
 Will mention everyone that opted-in for everyone-mentions separated by spaces.
 
-If user does not contain nickname, his ID will be present instead of nickname.
+If user does not have nickname, it will assign random name from `names` python library to his ID
 
 ![everybody command example](docs/everyone_command.png)
 
diff --git a/docker-compose.yml b/docker-compose.yml
new file mode 100755
index 0000000..21047b1
--- /dev/null
+++ b/docker-compose.yml
@@ -0,0 +1,37 @@
+version: "3.6"
+
+services:
+
+  database:
+    image: mongo:4.0.8
+    restart: unless-stopped
+    env_file:
+      - ./docker/config/database/database.env
+    volumes: 
+      - db-data:/data/db
+    ports:
+      - 27017:27017
+    networks:
+      - web
+
+  app:
+    build: .
+    command: python app.py
+    env_file:
+      - ./docker/config/app/app.env
+    volumes:
+      - ./src:/src
+    ports:
+      - 9000:9000
+    depends_on:
+      - database
+    networks:
+      - web
+    restart: on-failure
+
+networks:
+  web:
+    driver: bridge
+  
+volumes:
+  db-data:
\ No newline at end of file
diff --git a/docker/config/app/app.dist.env b/docker/config/app/app.dist.env
new file mode 100755
index 0000000..ad05a23
--- /dev/null
+++ b/docker/config/app/app.dist.env
@@ -0,0 +1,7 @@
+BOT_TOKEN=
+
+MONGODB_DATABASE=
+MONGODB_USERNAME=
+MONGODB_PASSWORD=
+MONGODB_HOSTNAME=localhost
+MONGODB_PORT=27017
\ No newline at end of file
diff --git a/docker/config/database/database.dist.env b/docker/config/database/database.dist.env
new file mode 100755
index 0000000..3594ee3
--- /dev/null
+++ b/docker/config/database/database.dist.env
@@ -0,0 +1,5 @@
+MONGO_INITDB_ROOT_USERNAME=
+MONGO_INITDB_ROOT_PASSWORD=
+MONGO_INITDB_DATABASE=
+MONGODB_DATA_DIR=/mongo/database
+MONDODB_LOG_DIR=
\ No newline at end of file
diff --git a/docker/logs b/docker/logs
new file mode 100755
index 0000000..76ec3ec
--- /dev/null
+++ b/docker/logs
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+[ -z "$1" ] && printf "\nPlease specify service name (ex. app)\n\n" && exit
+
+docker-compose logs -f "$@"
\ No newline at end of file
diff --git a/docs/commands.png b/docs/commands.png
old mode 100644
new mode 100755
diff --git a/docs/everyone_command.png b/docs/everyone_command.png
old mode 100644
new mode 100755
diff --git a/docs/everyone_noone_to_mention.png b/docs/everyone_noone_to_mention.png
old mode 100644
new mode 100755
diff --git a/docs/in_command.png b/docs/in_command.png
old mode 100644
new mode 100755
diff --git a/docs/in_command_already_opted_in.png b/docs/in_command_already_opted_in.png
old mode 100644
new mode 100755
diff --git a/docs/logo.png b/docs/logo.png
old mode 100644
new mode 100755
diff --git a/docs/out_command.png b/docs/out_command.png
old mode 100644
new mode 100755
diff --git a/docs/out_command_did_not_opt_in_before.png b/docs/out_command_did_not_opt_in_before.png
old mode 100644
new mode 100755
diff --git a/entrypoint.py b/entrypoint.py
deleted file mode 100644
index 2e270f8..0000000
--- a/entrypoint.py
+++ /dev/null
@@ -1,6 +0,0 @@
-from src.app import App
-
-if __name__ == "__main__":
-    app = App()
-
-    app.run()
diff --git a/runtime.txt b/runtime.txt
deleted file mode 100644
index a48890e..0000000
--- a/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.8.10
diff --git a/src/app.py b/src/app.py
old mode 100644
new mode 100755
index a27caca..70eea6c
--- a/src/app.py
+++ b/src/app.py
@@ -1,10 +1,9 @@
-from .config.credentials import bot_token
-from .config.handlers import handlers
-from .handlers.handlerInterface import HandlerInterface
+from config.credentials import bot_token
+from config.handlers import handlers
+from handlers.handlerInterface import HandlerInterface
 from telegram.ext.dispatcher import Dispatcher
 from telegram.ext import Updater
 
-
 class App:
     updater: Updater
     dispatcher: Dispatcher
@@ -14,6 +13,7 @@ class App:
 
     def run(self) -> None:
         self.registerHandlers()
+        
         self.updater.start_polling()
         self.updater.idle()
 
@@ -23,3 +23,9 @@ class App:
                 raise Exception('Invalid list of handlers provided. Handler must implement HandlerInterface')
 
             self.updater.dispatcher.add_handler(handler.getBotHandler())
+
+
+if __name__ == "__main__":
+    app = App()
+
+    app.run()
\ No newline at end of file
diff --git a/src/config/contents.py b/src/config/contents.py
old mode 100644
new mode 100755
diff --git a/src/config/credentials.py b/src/config/credentials.py
old mode 100644
new mode 100755
index 072318f..3bcc710
--- a/src/config/credentials.py
+++ b/src/config/credentials.py
@@ -5,10 +5,8 @@ load_dotenv()
 
 bot_token = os.environ['bot_token']
 
-firebaseConfig = {
-    "apiKey": os.environ['firebase_apiKey'],
-    "authDomain": os.environ['firebase_authDomain'],
-    "databaseURL": os.environ['firebase_databaseURL'],
-    "projectId": os.environ['firebase_projectId'],
-    "storageBucket": os.environ['firebase_storageBucket'],
-}
+MONGODB_DATABASE=os.environ['MONGODB_DATABASE']
+MONGODB_USERNAME=os.environ['MONGODB_USERNAME']
+MONGODB_PASSWORD=os.environ['MONGODB_PASSWORD']
+MONGODB_HOSTNAME=os.environ['MONGODB_HOSTNAME']
+MONGODB_PORT=os.environ['MONGODB_PORT']
diff --git a/src/config/handlers.py b/src/config/handlers.py
old mode 100644
new mode 100755
index a7d81d6..0ea3e9c
--- a/src/config/handlers.py
+++ b/src/config/handlers.py
@@ -1,6 +1,6 @@
-from ..handlers.inHandler import InHandler
-from ..handlers.outHandler import OutHandler
-from ..handlers.mentionHandler import MentionHandler
+from handlers.inHandler import InHandler
+from handlers.outHandler import OutHandler
+from handlers.mentionHandler import MentionHandler
 
 handlers = [
     InHandler(),
diff --git a/src/database/databaseClient.py b/src/database/databaseClient.py
new file mode 100755
index 0000000..97ac57e
--- /dev/null
+++ b/src/database/databaseClient.py
@@ -0,0 +1,30 @@
+from pymongo.errors import ServerSelectionTimeoutError
+from config.credentials import MONGODB_USERNAME, MONGODB_PASSWORD, MONGODB_DATABASE, MONGODB_HOSTNAME, MONGODB_PORT
+from pymongo import MongoClient
+from pymongo.database import Database
+from urllib.parse import quote_plus
+
+class DatabaseClient():
+    mongoClient: MongoClient
+    database: Database
+
+    def __init__(self) -> None:
+        uri = "mongodb://%s:%s@%s:%s/%s?authSource=admin" % (
+            MONGODB_USERNAME, quote_plus(MONGODB_PASSWORD),
+            MONGODB_HOSTNAME, MONGODB_PORT, MONGODB_DATABASE
+        )
+
+        self.mongoClient = MongoClient(uri)
+        self.database = self.mongoClient[MONGODB_DATABASE]
+
+    def insert(self, collection: str, data: dict) -> None:
+        self.database.get_collection(collection).insert_one(data)
+
+    def find(self, collection: str, query: dict) -> dict:
+        return self.database.get_collection(collection).find(query)
+
+    def findOne(self, collection: str, query: dict) -> dict:
+        return self.database.get_collection(collection).find_one(query)
+
+    def remove(self, collection: str, data: dict) -> None:
+        self.database.get_collection(collection).remove(data)
\ No newline at end of file
diff --git a/src/entities/chat.py b/src/entities/chat.py
new file mode 100755
index 0000000..ea6217e
--- /dev/null
+++ b/src/entities/chat.py
@@ -0,0 +1,28 @@
+from __future__ import annotations
+from typing import Optional
+
+
+class Chat():
+    id: str
+
+    def __init__(self, id: str) -> None:
+        self.id = id
+
+    def getId(self) -> str:
+        return self.id
+
+    def toDict(self) -> dict:
+        return {
+            '_id': self.id
+        }
+    
+    @staticmethod
+    def getMongoRoot() -> str:
+        return 'chat'
+
+    @staticmethod
+    def fromDocument(document: Optional[dict]) -> Optional[Chat]:
+        if not document:
+            return None
+
+        return Chat(document['_id'])
\ No newline at end of file
diff --git a/src/entities/chatPerson.py b/src/entities/chatPerson.py
new file mode 100755
index 0000000..3a38791
--- /dev/null
+++ b/src/entities/chatPerson.py
@@ -0,0 +1,34 @@
+from __future__ import annotations
+from typing import Optional
+
+
+class ChatPerson():
+    chat_id: str
+    person_id: str
+
+    def __init__(self, chatId: str, personId: str) -> None:
+        self.chat_id = chatId
+        self.person_id = personId
+
+    def getChatId(self) -> str:
+        return self.chat_id
+
+    def getPersonId(self) -> str:
+        return self.person_id
+
+    def toDict(self) -> dict:
+        return {
+            '_id': f'{self.chat_id}-{self.person_id}',
+            'chat_id': self.chat_id,
+            'person_id': self.person_id
+        }
+
+    @staticmethod
+    def getMongoRoot() -> str:
+        return 'chat_person'
+    
+    @staticmethod
+    def fromDocument(document: Optional[dict]) -> Optional[ChatPerson]:
+        if not document:
+            return None
+        return ChatPerson(document['chat_id'], document['person_id'])
\ No newline at end of file
diff --git a/src/entities/group.py b/src/entities/group.py
deleted file mode 100644
index 931491c..0000000
--- a/src/entities/group.py
+++ /dev/null
@@ -1,34 +0,0 @@
-from typing import Iterable
-from .user import User
-
-class Group():
-    __id: int
-    __users: Iterable[User] = []
-
-    def __init__(self, id: int) -> None:
-        self.__id = id
-
-    def getId(self) -> int:
-        return self.__id
-
-    def setUsers(self, users: Iterable[User]) -> None:
-        self.__users = users
-
-    def addUser(self, user: User) -> None:
-        self.__users.append(user)
-
-    def removeUser(self, user: User) -> None:
-        for index, groupUser in enumerate(self.__users):
-            if groupUser.getId() == user.getId():
-                del self.__users[index]
-
-    def getUsers(self) -> Iterable[User]:
-        return self.__users
-    
-    def hasUser(self, user: User) -> bool:
-        userIds = [int(groupUser.getId()) for groupUser in self.getUsers()]
-
-        if user.getId() in userIds:
-            return True
-
-        return False
\ No newline at end of file
diff --git a/src/entities/person.py b/src/entities/person.py
new file mode 100755
index 0000000..2c1cfdf
--- /dev/null
+++ b/src/entities/person.py
@@ -0,0 +1,44 @@
+from __future__ import annotations
+from abc import abstractmethod
+from typing import Optional
+import names
+
+
+class Person():
+    id: str
+    username: str
+
+    def __init__(self, id: str, username: Optional[str] = None) -> None:
+        self.id = id
+        
+        if not username:
+            self.username = names.get_first_name()
+        else:
+            self.username = username
+
+    def getId(self) -> str:
+        return self.id
+
+    def getUsername(self) -> str:
+        return self.username
+
+    def toDict(self, withUsername: bool = True) -> dict:
+        result = {
+            '_id': self.id
+        }
+
+        if withUsername:
+            result['username'] = self.username
+        
+        return result
+
+    @staticmethod
+    def getMongoRoot() -> str:
+        return 'person'
+
+    @staticmethod
+    def fromDocument(document: Optional[dict]) -> Optional[Person]:
+        if not document:
+            return None
+
+        return Person(document['_id'], document['username'])
\ No newline at end of file
diff --git a/src/entities/user.py b/src/entities/user.py
deleted file mode 100644
index 13808d2..0000000
--- a/src/entities/user.py
+++ /dev/null
@@ -1,19 +0,0 @@
-from typing import Optional
-
-class User():
-    __id: int
-    __username: Optional[str]
-    __groupId: int
-
-    def __init__(self, id: int, username: Optional[str]) -> None:
-        self.__id = id
-        self.__username = username
-
-    def getId(self) -> int:
-        return self.__id
-
-    def getUsername(self) -> Optional[str]:
-        return self.__username
-    
-    def getGroupId(self) -> int:
-        return self.__groupId
\ No newline at end of file
diff --git a/src/firebaseProxy.py b/src/firebaseProxy.py
deleted file mode 100644
index aa8db8c..0000000
--- a/src/firebaseProxy.py
+++ /dev/null
@@ -1,34 +0,0 @@
-import pyrebase
-from pyrebase.pyrebase import Database as FirebaseDB
-from .config.credentials import firebaseConfig
-
-
-class FirebaseProxy():
-    db: FirebaseDB
-
-    # Group specific values
-    group_index: str = 'groups'
-
-    # User specific values
-    id_index: str = 'id'
-    name_index: str = 'name'
-
-    def __init__(self) -> None:
-        firebase = pyrebase.pyrebase.initialize_app(firebaseConfig)
-        self.db = firebase.database()
-
-    def getChilds(self, *childs: str) -> FirebaseDB:
-        current = self.db
-
-        for child_index in childs:
-            current = current.child(child_index)
-        
-        return current
-
-    @staticmethod
-    def getGroupPath(groupId: int) -> str:
-        return f'{FirebaseProxy.group_index}/{groupId}'
-
-    @staticmethod
-    def getUserPath(userId: int, groupId: int) -> str:
-        return f'{groupId}_{userId}'
diff --git a/src/handlers/handlerInterface.py b/src/handlers/handlerInterface.py
old mode 100644
new mode 100755
index 3cad7ce..5a4607c
--- a/src/handlers/handlerInterface.py
+++ b/src/handlers/handlerInterface.py
@@ -16,3 +16,6 @@ class HandlerInterface:
 
     @abstractmethod
     def getCommandName(self) -> str: raise Exception('getCommandName method is not implemented')
+
+    def reply(self, update: Update, message: str) -> None:
+        update.effective_message.reply_markdown_v2(text=message)
diff --git a/src/handlers/inHandler.py b/src/handlers/inHandler.py
old mode 100644
new mode 100755
index 7bbfdca..49f5840
--- a/src/handlers/inHandler.py
+++ b/src/handlers/inHandler.py
@@ -1,12 +1,11 @@
-from ..config.contents import opted_in_successfully, opted_in_failed
-from ..entities.user import User
-from ..repositories.groupRepository import GroupRepository
-from .handlerInterface import HandlerInterface
+from config.contents import opted_in_successfully, opted_in_failed
+from repositories.relationRepository import RelationRepository
+from database.databaseClient import DatabaseClient
+from handlers.handlerInterface import HandlerInterface
 from telegram.ext.callbackcontext import CallbackContext
 from telegram.ext.commandhandler import CommandHandler
 from telegram.update import Update
 
-
 class InHandler(HandlerInterface):
     botHandler: CommandHandler
     commandName: str = 'in'
@@ -18,18 +17,19 @@ class InHandler(HandlerInterface):
         )
 
     def handle(self, update: Update, context: CallbackContext) -> None:
-        groupRepository = GroupRepository()
-        group = groupRepository.get(update.effective_chat.id)
-        user = User(update.effective_user.id, update.effective_user.username)
+        personId = update.effective_user.id
+        chatId = update.effective_chat.id
+        username = update.effective_user.username
 
-        if group.hasUser(user):
-            update.message.reply_markdown_v2(text=opted_in_failed)
+        relationRepository = RelationRepository()
+        relation = relationRepository.get(chatId, personId)
+
+        if relation:
+            self.reply(update, opted_in_failed)
             return
-
-        group.addUser(user)
-        groupRepository.save(group)
-
-        update.message.reply_markdown_v2(text=opted_in_successfully)
+        
+        relationRepository.save(chatId, personId, username)
+        self.reply(update, opted_in_successfully)
 
     def getBotHandler(self) -> CommandHandler:
         return self.botHandler
diff --git a/src/handlers/mentionHandler.py b/src/handlers/mentionHandler.py
old mode 100644
new mode 100755
index bcccc72..4cad530
--- a/src/handlers/mentionHandler.py
+++ b/src/handlers/mentionHandler.py
@@ -1,9 +1,9 @@
-from ..config.contents import mention_failed
-from ..entities.group import Group
-from ..entities.user import User
-from ..firebaseProxy import FirebaseProxy
-from ..repositories.groupRepository import GroupRepository
-from .handlerInterface import HandlerInterface
+from typing import Iterable
+from config.contents import mention_failed
+from entities.person import Person
+from handlers.handlerInterface import HandlerInterface
+from repositories.relationRepository import RelationRepository
+from repositories.personRepository import PersonRepository
 from telegram.ext.callbackcontext import CallbackContext
 from telegram.ext.commandhandler import CommandHandler
 from telegram.update import Update
@@ -20,11 +20,15 @@ class MentionHandler(HandlerInterface):
         )
 
     def handle(self, update: Update, context: CallbackContext) -> None:
-        groupId = update.effective_chat.id
-        groupRepository = GroupRepository()
-        mentionMessage = self.buildMentionMessage(groupRepository.get(id=groupId))
+        relationRepository = RelationRepository()
+        persons = relationRepository.getPersonsForChat(update.effective_chat.id)
+
+        if not persons:
+            self.reply(update, mention_failed)
+            return
+
+        self.reply(update, self.buildMentionMessage(persons))
 
-        update.message.reply_markdown_v2(text=mentionMessage)
 
     def getBotHandler(self) -> CommandHandler:
         return self.botHandler
@@ -32,11 +36,10 @@ class MentionHandler(HandlerInterface):
     def getCommandName(self) -> str:
         return self.commandName
 
-    def buildMentionMessage(self, group: Group) -> str:
+    def buildMentionMessage(self, persons: Iterable[Person]) -> str:
         result = ''
 
-        for user in group.getUsers():
-            username = user.getUsername() or user.getId()
-            result +=  f'*[{username}](tg://user?id={user.getId()})* '
+        for person in persons:
+            result +=  f'*[{person.getUsername()}](tg://user?id={person.getId()})* '
 
-        return result or mention_failed
+        return result
diff --git a/src/handlers/outHandler.py b/src/handlers/outHandler.py
old mode 100644
new mode 100755
index 8d3b5b1..f0597a5
--- a/src/handlers/outHandler.py
+++ b/src/handlers/outHandler.py
@@ -1,11 +1,11 @@
-from ..config.contents import opted_off_successfully, opted_off_failed
-from ..entities.user import User
-from ..repositories.groupRepository import GroupRepository
-from .handlerInterface import HandlerInterface
+from config.contents import opted_off_successfully, opted_off_failed
+from handlers.handlerInterface import HandlerInterface
 from telegram.ext.callbackcontext import CallbackContext
 from telegram.ext.commandhandler import CommandHandler
 from telegram.update import Update
 
+from repositories.relationRepository import RelationRepository
+
 
 class OutHandler(HandlerInterface):
     botHandler: CommandHandler
@@ -18,18 +18,18 @@ class OutHandler(HandlerInterface):
         )
 
     def handle(self, update: Update, context: CallbackContext) -> None:
-        groupRepository = GroupRepository()
-        group = groupRepository.get(update.effective_chat.id)
-        user = User(update.effective_user.id, update.effective_user.username)
+        personId = update.effective_user.id
+        chatId = update.effective_chat.id
 
-        if group.hasUser(user):
-            group.removeUser(user)
-            groupRepository.save(group)
-            
-            update.message.reply_markdown_v2(text=opted_off_successfully)
+        relationRepository = RelationRepository()
+        relation = relationRepository.get(chatId, personId)
+        
+        if not relation:
+            self.reply(update, opted_off_failed)
             return
-
-        update.message.reply_markdown_v2(text=opted_off_failed)
+        
+        relationRepository.remove(relation)
+        self.reply(update, opted_off_successfully)
 
     def getBotHandler(self) -> CommandHandler:
         return self.botHandler
diff --git a/src/repositories/chatRepository.py b/src/repositories/chatRepository.py
new file mode 100755
index 0000000..ec57f0a
--- /dev/null
+++ b/src/repositories/chatRepository.py
@@ -0,0 +1,18 @@
+from database.databaseClient import DatabaseClient
+from entities.chat import Chat
+from typing import Optional
+
+class ChatRepository:
+    database: DatabaseClient
+
+    def __init__(self) -> None:
+        self.database = DatabaseClient()
+
+    def get(self, id: str) -> Optional[Chat]:
+        chat = Chat(id)
+        search = self.database.findOne(Chat.getMongoRoot(), chat.toDict())
+        
+        return Chat.fromDocument(search)
+        
+    def save(self, chat: Chat) -> None:
+        self.database.insert(Chat.getMongoRoot(), chat.toDict())
\ No newline at end of file
diff --git a/src/repositories/groupRepository.py b/src/repositories/groupRepository.py
deleted file mode 100644
index 20d13dd..0000000
--- a/src/repositories/groupRepository.py
+++ /dev/null
@@ -1,48 +0,0 @@
-from ..entities.group import Group
-from ..entities.user import User
-from ..firebaseProxy import FirebaseProxy
-
-
-class GroupRepository():
-    firebase: FirebaseProxy
-    
-    def __init__(self) -> None:
-        self.firebase = FirebaseProxy()
-
-    def get(self, id: int) -> Group:
-        group = Group(id)
-        fbData = self.firebase.getChilds(FirebaseProxy.group_index, id).get()
-        users = []
-
-        for userData in fbData.each() or []:
-            userData = userData.val()
-            users.append(
-                User(
-                    userData.get(FirebaseProxy.id_index),
-                    userData.get(FirebaseProxy.name_index)
-                )
-            )
-    
-        group.setUsers(users)
-
-        return group
-
-    def save(self, group: Group) -> None:
-        users = {}
-
-        if not group.getUsers():
-            self.remove(group)
-
-        for user in group.getUsers():
-            users[user.getId()] = {
-                FirebaseProxy.id_index: user.getId(),
-                FirebaseProxy.name_index: user.getUsername()
-            }
-        
-        self.firebase.getChilds(
-            FirebaseProxy.group_index,
-            group.getId()
-        ).update(users)
-
-    def remove(self, group: Group) -> None:
-        self.firebase.getChilds(FirebaseProxy.group_index, group.getId()).remove()
\ No newline at end of file
diff --git a/src/repositories/personRepository.py b/src/repositories/personRepository.py
new file mode 100755
index 0000000..b3ee6bb
--- /dev/null
+++ b/src/repositories/personRepository.py
@@ -0,0 +1,27 @@
+from database.databaseClient import DatabaseClient
+from entities.person import Person
+from typing import Iterable, Optional
+
+class PersonRepository:
+    database: DatabaseClient
+
+    def __init__(self) -> None:
+        self.database = DatabaseClient()
+
+    def get(self, id: str) -> Optional[Person]:
+        person = Person(id)
+        search = self.database.findOne(Person.getMongoRoot(), person.toDict(False))
+        
+        return Person.fromDocument(search)        
+        
+    def find(self, query: dict) -> Iterable[Person]:
+        result = []
+        search = self.database.find(Person.getMongoRoot(), query)
+
+        for document in search:
+            result.append(Person.fromDocument(document))
+
+        return result
+
+    def save(self, person: Person) -> None:
+        self.database.insert(Person.getMongoRoot(), person.toDict())
\ No newline at end of file
diff --git a/src/repositories/relationRepository.py b/src/repositories/relationRepository.py
new file mode 100755
index 0000000..3482544
--- /dev/null
+++ b/src/repositories/relationRepository.py
@@ -0,0 +1,56 @@
+from typing import Iterable, Optional
+from database.databaseClient import DatabaseClient
+from entities.chat import Chat
+from entities.chatPerson import ChatPerson
+from entities.person import Person
+from repositories.personRepository import PersonRepository
+from repositories.chatRepository import ChatRepository
+
+
+class RelationRepository():
+    client: DatabaseClient
+
+    def __init__(self) -> None:
+        self.client = DatabaseClient()
+
+    def get(self, chatId: str, personId: str) -> Optional[ChatPerson]:
+        relation = ChatPerson(chatId, personId)
+        search = self.client.findOne(ChatPerson.getMongoRoot(), relation.toDict())
+        
+        return ChatPerson.fromDocument(search)
+
+    def save(self, chatId: str, personId: str, username: Optional[str] = None) -> None:
+        relation = ChatPerson(chatId, personId)
+
+        self.client.insert(ChatPerson.getMongoRoot(), relation.toDict())
+        personRepository = PersonRepository()
+        person = personRepository.get(personId)
+
+        if not person:
+            person = Person(personId, username)
+            personRepository.save(person)
+
+        chatRepository = ChatRepository()
+        chat = chatRepository.get(chatId)
+        
+        if not chat:
+            chat = Chat(chatId)
+            chatRepository.save(chat)
+
+    def getPersonsForChat(self, chatId: str) -> Iterable[ChatPerson]:
+        result = []
+        relations = self.client.find(ChatPerson.getMongoRoot(), {'chat_id': chatId})
+        
+        search = {}
+        for relation in relations:
+            search['_id'] = relation['person_id']
+
+        if not search:
+            return result
+
+        personRepository = PersonRepository()
+        return personRepository.find(search)
+
+    def remove(self, relation: ChatPerson) -> None:
+        self.client.remove(ChatPerson.getMongoRoot() ,relation.toDict())
+
diff --git a/src/repositories/userRepository.py b/src/repositories/userRepository.py
deleted file mode 100644
index 7155b4e..0000000
--- a/src/repositories/userRepository.py
+++ /dev/null
@@ -1,12 +0,0 @@
-from ..firebaseProxy import FirebaseProxy
-
-
-class UserRepository():
-    firebaseProxy: FirebaseProxy
-
-    def __init__(self) -> None:
-        self.firebaseProxy = FirebaseProxy()
-
-    # TODO : this repository needs to handle user save/deletion/update
-    # right now, all of those above is handled by GroupRepository
-    
\ No newline at end of file
diff --git a/requirements.txt b/src/requirements.txt
old mode 100644
new mode 100755
similarity index 63%
rename from requirements.txt
rename to src/requirements.txt
index af1197a..81d707c
--- a/requirements.txt
+++ b/src/requirements.txt
@@ -1,3 +1,4 @@
 python-dotenv==0.19.0
 python-telegram-bot==13.7
-Pyrebase==3.0.27
+pymongo==3.12.0
+names==0.3.0
\ No newline at end of file