Hi,
I am trying to understand the way to create a many to many
relationship in datastore. Let me take an example to start with.
Suppose I have users and communities as two entities. A user can join
as many communities as he wants and a community can have a lot of
users.
------------------ -------------------------
| | | |
| USER | m --- n | COMMUNITY |
| | | |
------------------ -------------------------
First way of doing it
-------------------------------
class User {
String emailID // primary key for user
List<Key> communitiesJoined
......
}
class Community {
Key communityID // primary key for community
List<String> usersInCommunity
}
User Joins community ---
user.communitiesJoined.add(coummunityiD)
&&
community.usersInCommunity.add(userID)
Get Communities Joined By User --
user.communitiesJoined
Get Users in a community --
community.usersInCommnity
Second way
---------------------
class User {
String emailID // primary key for user
}
class Community {
Key communityID // primay key for community
}
class UserCommunityMapping {
String emailID
Key communityID
}
User Joins community ---
UserCommunityMapping ucm = new UserCommunityMapping()
ucm.emailID = user.emailID
ucm.communityID = community.communityID
Get Communities Joined By User --
select emailID from UserCommunityMapping where communityID =
coummunity.communityID
Get Users in a community --
select coummunityID from UserCommunityMapping where emailID =
user.userID
Now, can somebody tell me which is the better way to do it in
appstore? Below are the categories.
Performance during query?
Memory utilization?
Easy way to query?
If there is any other way, you can share that as well.
Thanks in advance.
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