Users from traditional RDBMS usually wonder how to do joins in DynamoDB. The simple answer is that you have to do it manually.
That is, get item from table A and use its attribute to query items from table B.
const result = dynamoDb.get({
Key: {
id: topicId
},
TableName: 'topics'
});
const item = result.Item;
const forumId = item.forumId;
const result2 = dynamoDb.get({
Key: {
id: forumId
},
TableName: 'forums'
});
// or you may query against a secondary index
const result2 = dynamoDb.query({
KeyConditionExpression: '#someId = :foreignId',
ExpressionAttributeNames: { '#someId': 'someId' },
ExpressionAttributeValues: { ':foreignId': foreignId },
IndexName: 'mySecondaryIndex',
TableName: 'myTableB'
})
