Partition key and sort key in AWS - Mini Project: Build & Apply

Partition key and sort key

📖 Scenario: You are building a simple database table in AWS DynamoDB to store information about books in a library. Each book has a unique ISBN number and a title. You want to organize the table so that you can quickly find books by their ISBN and also sort them by their title within the same ISBN.

🎯 Goal: Create a DynamoDB table with a partition key and a sort key. The partition key should be ISBN to uniquely identify each book. The sort key should be Title to allow sorting books by their title within the same ISBN.

📋 What You'll Learn

Create a DynamoDB table named LibraryBooks.

Use ISBN as the partition key of type string.

Use Title as the sort key of type string.

Set the billing mode to PAY_PER_REQUEST for simplicity.

💡 Why This Matters

🌍 Real World

DynamoDB tables with partition and sort keys are used in many applications to store and query data efficiently, such as user profiles, product catalogs, and event logs.

💼 Career

Understanding partition and sort keys is essential for cloud architects and developers working with AWS DynamoDB to design scalable and performant NoSQL databases.

1

Create the basic table structure

Create a DynamoDB table resource named LibraryBooks with an empty AttributeDefinitions and KeySchema arrays.

AWS

Resources:
  LibraryBooks:
    Type: AWS::DynamoDB::Table
    Properties:
      AttributeDefinitions: []
      KeySchema: []
      BillingMode: PAY_PER_REQUEST
# Your code here

Hint

Start by defining the DynamoDB table resource with empty attribute and key schema lists.

2

Define the partition key attribute

Add an attribute definition for the partition key named ISBN of type S (string) inside AttributeDefinitions. Also add a key schema entry for the partition key with AttributeName as ISBN and KeyType as HASH.

AWS

Resources:
  LibraryBooks:
    Type: AWS::DynamoDB::Table
    Properties:
      AttributeDefinitions:
        # Add partition key attribute definition here
      KeySchema:
        # Add partition key schema here
      BillingMode: PAY_PER_REQUEST
# Your code here

Hint

The partition key is the main key to find items. Use HASH for partition key.

3

Add the sort key attribute

Add an attribute definition for the sort key named Title of type S inside AttributeDefinitions. Also add a key schema entry for the sort key with AttributeName as Title and KeyType as RANGE.

AWS

Resources:
  LibraryBooks:
    Type: AWS::DynamoDB::Table
    Properties:
      AttributeDefinitions:
        - AttributeName: ISBN
          AttributeType: S
        # Add sort key attribute definition here
      KeySchema:
        - AttributeName: ISBN
          KeyType: HASH
        # Add sort key schema here
      BillingMode: PAY_PER_REQUEST
# Your code here

Hint

The sort key helps sort items with the same partition key. Use RANGE for sort key.

4

Complete the table configuration

Ensure the table name is set to LibraryBooks in the Properties section.

AWS

Resources:
  LibraryBooks:
    Type: AWS::DynamoDB::Table
    Properties:
      AttributeDefinitions:
        - AttributeName: ISBN
          AttributeType: S
        - AttributeName: Title
          AttributeType: S
      KeySchema:
        - AttributeName: ISBN
          KeyType: HASH
        - AttributeName: Title
          KeyType: RANGE
      BillingMode: PAY_PER_REQUEST
      # Add TableName property here
# Your code here

Hint

Set the TableName property to the exact table name.

Practice

1.

What is the main role of a partition key in AWS DynamoDB?

easy

A. It groups data into partitions for efficient storage and retrieval.

B. It sorts data within a partition in ascending order.

C. It encrypts the data before storing it.

D. It defines the backup schedule for the table.

Solution

1. Step 1: Understand partition key purpose

   The partition key is used to group data into partitions, which helps DynamoDB distribute and store data efficiently.

2. Step 2: Differentiate from sort key

   The sort key orders data inside each partition but does not group data across partitions.

3. Final Answer:

   It groups data into partitions for efficient storage and retrieval. -> Option A

4. Quick Check:

   Partition key = groups data [OK]

Hint: Partition key groups data, sort key orders it inside partitions [OK]

Common Mistakes:

• Confusing partition key with sort key
• Thinking partition key sorts data
• Assuming partition key controls backups

2.

Which of the following is the correct way to define a DynamoDB table with a partition key named UserId and a sort key named OrderDate in AWS CLI?

aws dynamodb create-table --table-name Orders --attribute-definitions AttributeName=UserId,AttributeType=S AttributeName=OrderDate,AttributeType=S --key-schema ...

easy

A. --key-schema AttributeName=UserId,KeyType=HASH AttributeName=OrderDate,KeyType=RANGE

B. --key-schema AttributeName=OrderDate,KeyType=HASH AttributeName=UserId,KeyType=RANGE

C. --key-schema AttributeName=UserId,KeyType=RANGE AttributeName=OrderDate,KeyType=HASH

D. --key-schema AttributeName=OrderDate,KeyType=RANGE AttributeName=UserId,KeyType=HASH

Solution

1. Step 1: Identify partition and sort key roles

   The partition key uses KeyType=HASH and the sort key uses KeyType=RANGE in DynamoDB key schema.

2. Step 2: Match keys to names

   UserId is the partition key (HASH), OrderDate is the sort key (RANGE).

3. Final Answer:

   --key-schema AttributeName=UserId,KeyType=HASH AttributeName=OrderDate,KeyType=RANGE -> Option A

4. Quick Check:

   Partition=HASH, Sort=RANGE [OK]

Hint: Partition key = HASH, sort key = RANGE in key schema [OK]

Common Mistakes:

• Swapping HASH and RANGE key types
• Mixing up partition and sort key names
• Using wrong attribute types

3.

Given a DynamoDB table with CustomerId as partition key and InvoiceDate as sort key, what will the following query return?

Query: KeyConditionExpression = "CustomerId = :cid AND InvoiceDate > :date"

Assuming :cid is '123' and :date is '2023-01-01'.

medium

A. All invoices for customer '123' regardless of date.

B. All invoices for customer '123' with dates after January 1, 2023.

C. All invoices for all customers with dates after January 1, 2023.

D. All invoices with dates before January 1, 2023.

Solution

1. Step 1: Understand KeyConditionExpression

   The query filters items where partition key CustomerId equals '123' and sort key InvoiceDate is greater than '2023-01-01'.

2. Step 2: Interpret the filter effect

   This returns all invoices for customer '123' with InvoiceDate after January 1, 2023.

3. Final Answer:

   All invoices for customer '123' with dates after January 1, 2023. -> Option B

4. Quick Check:

   Partition key = '123' AND sort key > '2023-01-01' [OK]

Hint: Partition key filters customer, sort key filters date range [OK]

Common Mistakes:

• Ignoring partition key filter
• Assuming query returns all customers
• Confusing greater than with less than

4.

What is wrong with this DynamoDB key schema definition?

--attribute-definitions AttributeName=OrderId,AttributeType=S AttributeName=OrderDate,AttributeType=S --key-schema AttributeName=OrderDate,KeyType=HASH AttributeName=OrderId,KeyType=RANGE

medium

A. Attribute names cannot contain uppercase letters.

B. Attribute types must be different for partition and sort keys.

C. KeyType values must both be HASH for composite keys.

D. Partition key and sort key are swapped; OrderId should be HASH, OrderDate RANGE.

Solution

1. Step 1: Check key roles

   Partition key must be HASH and sort key must be RANGE in key schema.

2. Step 2: Identify swapped keys

   OrderId should be the partition key (HASH), but here OrderDate is set as HASH and OrderId as RANGE, which is incorrect.

3. Final Answer:

   Partition key and sort key are swapped; OrderId should be HASH, OrderDate RANGE. -> Option D

4. Quick Check:

   Partition = HASH, Sort = RANGE order matters [OK]

Hint: Partition key always HASH, sort key always RANGE [OK]

Common Mistakes:

• Swapping HASH and RANGE key types
• Assuming attribute types must differ
• Thinking uppercase letters are invalid

5.

You want to design a DynamoDB table to store user activity logs. Each user can have multiple logs per day. Which key design is best to efficiently query all logs for a user on a specific day?

hard

A. Partition key: UserId, Sort key: ActivityDateTime

B. Partition key: ActivityDateTime, Sort key: UserId

C. Partition key: UserId_ActivityDate, Sort key: ActivityTime

D. Partition key: ActivityType, Sort key: UserId

Solution

1. Step 1: Understand query needs

   You want to query logs by user and by specific day efficiently.

2. Step 2: Design keys for efficient queries

   Combining UserId and ActivityDate as partition key groups logs per user per day. Using ActivityTime as sort key orders logs within that day.

3. Final Answer:

   Partition key: UserId_ActivityDate, Sort key: ActivityTime -> Option C

4. Quick Check:

   Composite partition key groups user-day logs [OK]

Hint: Combine user and date in partition key for day queries [OK]

Common Mistakes:

• Using ActivityDateTime as partition key alone
• Swapping partition and sort keys
• Not combining keys to match query pattern