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data-model-assumptions.md

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Data model assumptions

When trying to generalize a concept, there has to be some assumptions. In this case, the table structure follows the general ideas about hierarchical data overloading the partition and sort keys as well as the GSI.

  • Generic partition key "PK" string.
  • Generic sort key "SK" string.
  • Generic attribute "GSI1" string.
  • GSI partition key is "GSI1".
  • GSI sort key is also "SK".
  • GSI projects all attributes.
  • Other attributes such as ID, Name, Description, etc.

Table with sample data

PK (S) SK (S) GSI1 ID Name Description
USER#U1 METADATA#U1 USER U1 Abel
USER#U2 METADATA#U2 USER U2 Nestor
PROJECT#P1 METADATA#P1 PROJECT P1 Project 1 desc project 1
PROJECT#P2 METADATA#P2 PROJECT P2 Project 2 desc project 2
PROJECT#P3 METADATA#P3 PROJECT P3 Project 3 desc project 3
USER#U1 GAME#G1 G1 Game 1
USER#U1 GAME#G2 G2 Game 2

GSI with sample data

PK (S) GSI1 SK (S) SK ID Name Description
USER METADATA#U1 U1 Abel
USER METADATA#U2 U2 Nestor
PROJECT METADATA#P1 P1 Project 1 desc project 1
PROJECT METADATA#P2 P2 Project 2 desc project 2
PROJECT METADATA#P3 P3 Project 3 desc project 3

Queries

  • Single item given the ID: Table PK = ENTITY#ID, SK = METADATA#ID

    • Get User U1: Table PK = USER#U1, SK = METADATA#U1
    • Get Project P1: Table PK = PROJECT#P1, SK = METADATA#P1
    • Get Game G1 for User U1: Table PK = USER#U1, SK = GAME#G1

  • Multiple items of one type: GSI PK = ENTITY

    • Get all users: GSI PK = USER
    • Get all projects: GSI PK = PROJECT

  • Item collection by parent ID: Table PK = PARENT_ENTITY#ID, SK = ENTITY#ID

    • Get all games by user U1 : Table PK = USER#U1, SK begins_with GAME

Creating the table - AWS CLI

Use aws dynamodb create-table command to create a table.

$ aws dynamodb create-table \
--table-name dynamodb_test_table \
--attribute-definitions \
    AttributeName=PK,AttributeType=S \
    AttributeName=SK,AttributeType=S \
    AttributeName=GSI1,AttributeType=S \
--key-schema \
    AttributeName=PK,KeyType=HASH \
    AttributeName=SK,KeyType=RANGE \
--provisioned-throughput \
    ReadCapacityUnits=1,WriteCapacityUnits=1 \
--global-secondary-indexes \
IndexName=GSI1,KeySchema=["{AttributeName=GSI1,KeyType=HASH},{AttributeName=SK,KeyType=RANGE}"],\
Projection="{ProjectionType=ALL}",\
ProvisionedThroughput="{ReadCapacityUnits=1,WriteCapacityUnits=1}"

Optionally, wait for the table to be active.

$ aws dynamodb wait table-exists --table-name dynamodb_test_table

Creating the table - CloudFormation

  # DynamoDb table
  DynamoDbTestTable:
    Type: AWS::DynamoDB::Table
    Properties: 
      KeySchema: 
        - AttributeName: PK
          KeyType: HASH
        - AttributeName: SK
          KeyType: RANGE
      AttributeDefinitions:
        - AttributeName: PK
          AttributeType: S
        - AttributeName: SK
          AttributeType: S
        - AttributeName: GSI1
          AttributeType: S
      ProvisionedThroughput:
        ReadCapacityUnits: 1
        WriteCapacityUnits: 1
      GlobalSecondaryIndexes:
        - IndexName: GSI1
          KeySchema: 
            - AttributeName: GSI1
              KeyType: HASH
            - AttributeName: SK
              KeyType: RANGE
          Projection: 
            ProjectionType: ALL
          ProvisionedThroughput: 
            ReadCapacityUnits: 1
            WriteCapacityUnits: 1