Inner Joins between tables with no Relationship

General
1

Hello,

I am new to Backendless and I have read all the documentation about relations, but I can’t figure out a way to solve this problem. I have also read FAQ’s but they are targeting different situations. I need a solution for this specific case. So I have two tables Users and FriendRequst. These two tables are not in relationship with each other.

Users Table
ObjectId
Name (STRING)
Password (STRING)
Image

FriendRequest Table
toUser (STRING) // this column contains ObjectId of User to whom friend request is send
fromUser (STRING) // this column contains ObjectId of User who has send friend request
accepted (BOOLEAN)

Now I want to do two things
(1) Make a call to FriendRequest Table that gets a collection of friend requests to specific User by using its ObjectId (for example: currentUserId)

BackendlessDataQuery query = new BackendlessDataQuery();
query.setWhereClause(String.format(“toUser = ‘%s’”, currentUserId));

(2) Now I want to use some method that can get me BackendlessUser Objects for the collection of friend requests from USER Table

NOTE:
I have attached pictures of my tables to make it more clear
( Sorry if my explanation is not clear )

FriendRequest.PNG
FriendRequest.PNG1047×191 17.4 KB

01.PNG
01.PNG1007×353 27.9 KB

2

Hello,

You would need to compose a query with the following whereClause:

objectId IN (‘value1’, ‘value2’, ‘value3’… )

That is you would need to iterate over FriendRequest objects, and build the whereClause for the values in fromUser/toUser, then run the query against the Users table.

Regards,
Mark

3

Hello Mark,

Thank you for your reply, I have tried this approach but it not time efficient, if I have 500 incoming friend request to a single user. I have use another approach in SQL and that works really quick with a single call, but I don’t know if Backendless support INNER JOINS.

This is what I am using in SQL

SELECT DISTINCT u.name, u.image
FROM Users u
JOIN FriendRequest f on f.from_user = u.objectID
WHERE f.to_user = currrentUserId;

Can you please tell me if the above approach is possible to execute in Backendless?

4

Backendless does not support inner joins. You would need to organize your storage and data structures to optimize data retrieval.

Regards,
Mark