The document discusses data structures and caching strategies for tree structures. It describes using a tree structure of groups, widgets, and structures to represent hierarchical data. Structures belong to groups and can have child structures. The document outlines approaches for moving and sorting child structures, sharing structures between users, setting permissions, and caching strategies like caching only one level and invalidating caches during updates to maintain consistency.

1. Sorting, moving, sharing and caching
in complex tree structure
Olga Scott
@olga_scott

2. Tree structure
- Group
- Widget
- Structure

3. Structure example
5
2
Structure:
belongs_to :group
belongs_to :child, polymorphic: true
{
id: 8,
group_id: 5,
child_id: 2,
child_type: “Widget”,
user_id: nil,
position: 213 - ranked_model Gem
}

4. Moving children
5
7
{
id: 19,
group_id: 5,
child_id: 7,
child_type: “Group”,
user_id: nil
}
{
id: 19,
group_id: 10,
child_id: 7,
child_type: “Group”,
user_id: nil
}
10

5. Moving child
5
7
10

6. Sorting children
{
id: 19,
group_id: 1,
child_id: 5,
child_type: “Group”,
position: -123
}
{
id: 19,
group_id: 1,
child_id: 5,
child_type: “Group”,
position: 269
}
1
5 9
-123 12 941
1
5 9
12 269 941

7. Sharing
U1 U2

8. Sharing
U1 U2
{
id: 19,
group_id: 5,
user_id: 1,
child_id: 9,
child_type: “Group”,
position: 123
}
5 15
9
{
id: 31,
group_id: 15,
user_id: 2,
child_id: 9,
child_type: “Group”,
position: -987
}

9. Permissions
U1 U2{
group_id: nil,
user_id: 1,
<..>
}
{
group_id: nil,
user_id: 2,
<..>
}
{
group_id: 9,
user_id: 2,
<..>
}
96
{
group_id: 6,
user_id: 1,
<..>
}

10. Russian Doll Caching
• Caching only one level
• Invalidating ”children” cache of
parent on after_commit
• Invalidating ”parent” cache of
all children on after_commit for
all users
• Getting all content using
recursion

11. Fetching cached children
def children
Rails.cache.fetch("children-for-Group-id-#{self.id}") {
structures = self.structures.by_position
structures.map{|structure| structure.child}.compact
}
end

12. Fetching cached parent
def parent(user)
Rails.cache.fetch("parent-for-#{self.class.name}-id-#{self.id}-for-user-id-#{user.id}") {
parent_structure = find_parent_structure_for_user(user)
parent_structure.group
}
end
U1 U2

13. Thank you!
Olga Scott
@olga_scott