database-structure.json

//This is an example of structure in Firestore for a social-media structure with likes, comments and posts
//Feel free to commit, or suggest changes.
{
  //Collection
  "Posts": {
    //Documents
    "postId_1": {
      //Post POJO
      "creationDate": "15 of october, 2017 11:17:25 UTC+2",
      "commentsCount": 1,
      "likesCount": 1,
      "content": "content",
      "author": {
        "fullname": "User 1",
        "photoUrl": "https://.....",
        "uid": "userId_1"
      },
      //Sub-collections
      "Comments": {
        //Documents
        "commentId_1 ": {
          "author": {
            "fullname": "User 2",
            "photoUrl": "https://.....",
            "uid": "userId_2"
          },
          "postAuthorId": "userId_1",
          //Keep track of the author of the post, to avoid nested queries later
          "text": "Test comment",
          "timestamp": "15 of october, 2017 15:17:25 UTC+2"
        }
      },
      "Likes": {
        //Documents
        "likeId_1": {
          "author": {
            "fullname": "User 2",
            "photoUrl": "https://.....",
            "uid": "userId_2"
          },
          "postAuthorId": "userId_1",
          //Keep track of the author of the post, to avoid nested queries later
          "timestamp": "15 of october, 2017 15:17:25 UTC+2"
        }
      }
    },
    "postId_2": {},
    "postId_3": {},
    //Collection
    "PrivateUserData": {
      //Documents
      "userId_1": {
        "accountCreationDate": "10 of october, 2017, 16:04:37 UTC+2",
        "email": "test@gmail.com",
        "photoUrl": "https://.....",
        "lastLogin": "12 of october, 2017, 13:04:37 UTC+2",
        "messagingTokens": [
          "messagingToken_1",
          "messagingToken_2"
        ],
        //Feed is a subcollection which contains denormalized data from the posts of the users that we are following
        //You could save here just the Id's and later go for a nested query or store the whole POJO, when we are using
        //Firebase Firestore and we will pay in order of the number or operations, I will suggest denormalized the data
        //and later edit the data with atomic functions (when the username or photoUrl are changed, or the post is edited)

        //In the end an user doesn't change their profile picture or name quite often, so even if it's an expensive update for a
        //lot of references, it will be lower than go for nested queries every time we will retrieve posts, comments, likes...
        "Feed": {
          //Same data than original pojo
          "postId-1": {
            "creationDate": "15 of october, 2017 11:17:25 UTC+2",
            "commentsCount": 1,
            "likesCount": 1,
            "content": "content",
            "author": {
              "fullname": "User 1",
              "photoUrl": "https://.....",
              "uid": "userId_1"
            }
          },
          "postId-2": {}
        },
        //Events is a subcollection which contains information about the social events from an user, such as new followers,
        //comments, likes.... also it's a way to keep track that your user already have been notified for that kind of event.
        // If there is already an event of type "Follow" from the User 2, even if he unfollow, and follow our user again, we will
        //know that there is no need to send a notificacion again.
        "Events": {
          //Documents
          "eventId_1": {
            "kind": "follow",
            "interactionUserName": "User 2",
            "interactionUserProfilePicture": "https://.....",
            "interactionUserId": "userId_2",
            "interactionRef": "userId_2",
            //Here we are storing the key that we will need for the notification intent. An userId for follows, and a PostId for comments or likes.
            "timestamp": "15 of october, 2017 11:17:25 UTC+2"
          }
        },
        //The next three subcollections are just to keep references from the places where we have denormalized data for this user, in this way we could retrieve later the comments,
        //likes and posts to update the reference if needed. In other hand, the events could be also stored here, but right now we can query the by interactionUserId.
        //In the same way with the Followers and Following from PublicUserData, we have the ids already stored there. We just need to retrieve them and edit the denormalized data.
        "AuthorOfComments": {
          "commentId_1": {
            "timeStamp": "15 of october, 2017 11:17:25 UTC+2"
          }
        },
        "AuthorOfLikes": {
          "likeId_1": {
            "timeStamp": "15 of october, 2017 11:17:25 UTC+2"
          }
        },
        "AuthorOfPosts": {
          "postId_1": {
            "timeStamp": "15 of october, 2017 11:17:25 UTC+2"
          }
        }
      }
    },
    "userId_2": {},
    "userId_3": {}
  },
  //Collection
  "PublicUserData": {
    //Documents
    "userId_1": {
      "followersCount": 3,
      "followingCount": 1,
      "photoUrl": "https://.....",
      "username": "User 1",
      //Sub-collections
      "Followers": {
        //If you know that your followers and following will never grow to much(around more than 36K of keys)
        //and surpass the Firestore 1MB document limit, you could store the Id's and the denormalized data in an array.
        "userId_2": {
          "photoUrl": "https://.....",
          "username": "User 2"
        }
      },
      "Following": {
        //Documents
        "userId_3": {
          "photoUrl": "https://.....",
          "username": "User 3"
        }
      }
    },
    "userId_2": {
    },
    "userId_3": {
    }
  }
}