Hierarchical data modeling in DynamoDB - Step-by-Step Execution

Concept Flow - Hierarchical data modeling

Start with Root Item

↓

Add Child Items with Parent ID

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Query by Parent ID to get Children

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Repeat for deeper levels

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Traverse hierarchy by querying each level

Hierarchical data modeling stores items with parent-child links, allowing queries to retrieve children by referencing parent IDs step-by-step.

Execution Sample

DynamoDB

Table: Employees
PK: EmployeeID
Attributes: Name, ManagerID

Insert:
{EmployeeID: 1, Name: 'Alice', ManagerID: null}
{EmployeeID: 2, Name: 'Bob', ManagerID: 1}
{EmployeeID: 3, Name: 'Carol', ManagerID: 1}

Query: Get employees where ManagerID = 1

This code models employees with managers as parents and queries employees reporting to Alice.

Execution Table

Step	Action	Query Condition	Result Items
1	Insert root employee Alice	N/A	{EmployeeID:1, Name:'Alice', ManagerID:null}
2	Insert child employee Bob	N/A	{EmployeeID:2, Name:'Bob', ManagerID:1}
3	Insert child employee Carol	N/A	{EmployeeID:3, Name:'Carol', ManagerID:1}
4	Query employees with ManagerID=1	ManagerID=1	[{EmployeeID:2, Name:'Bob'}, {EmployeeID:3, Name:'Carol'}]
5	Query employees with ManagerID=2	ManagerID=2	[]
6	End of queries	No more children	No results

💡 No more child employees found for queried ManagerID, traversal ends.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	Final
Employees Table	Empty	Alice, Bob inserted	Alice, Bob, Carol inserted	Alice, Bob, Carol	Alice, Bob, Carol	Alice, Bob, Carol
Query Result	None	None	None	[Bob, Carol]	[]	[]

Key Moments - 2 Insights

Why does querying ManagerID=2 return no results?

Because no employees have ManagerID=2 in the table as shown in execution_table row 5, so the query returns an empty list.

How do we find all employees under Alice?

By querying employees where ManagerID=1 (Alice's EmployeeID), as shown in execution_table row 4, which returns Bob and Carol.

Visual Quiz - 3 Questions

Look at the execution_table, what items are returned when querying ManagerID=1?

A [{EmployeeID:1, Name:'Alice'}]

B [{EmployeeID:2, Name:'Bob'}, {EmployeeID:3, Name:'Carol'}]

C []

D [{EmployeeID:3, Name:'Carol'}]

💡 Hint

Check execution_table row 4 under 'Result Items' for ManagerID=1 query.

At which step does the table contain the employee Carol?

A After Step 3

B After Step 2

C After Step 1

D After Step 4

💡 Hint

Look at execution_table rows 2 and 3 for when Bob and Carol are inserted.

If we add an employee Dave with ManagerID=2, what will querying ManagerID=2 return?

A []

B [{EmployeeID:2, Name:'Bob'}]

C [{EmployeeID:4, Name:'Dave'}]

D [{EmployeeID:3, Name:'Carol'}]

💡 Hint

Adding Dave with ManagerID=2 means querying ManagerID=2 returns Dave, unlike current empty result in execution_table row 5.

Concept Snapshot

Hierarchical data modeling in DynamoDB:
- Store items with a unique ID and a ParentID (e.g., ManagerID)
- Root items have null ParentID
- Query children by filtering on ParentID
- Repeat queries to traverse deeper levels
- Enables tree-like data representation in flat tables

Full Transcript

Hierarchical data modeling in DynamoDB means storing data items with links to their parent items using a field like ManagerID. The root item has no parent (null). When we want to find children of a parent, we query items where the ParentID equals the parent's ID. For example, Alice has EmployeeID 1 and no manager. Bob and Carol have ManagerID 1, so they are Alice's children. Querying for ManagerID=1 returns Bob and Carol. If we query for ManagerID=2, no children exist yet, so the result is empty. This way, we can build and traverse a hierarchy step-by-step by querying each level's children.