How to query AWS DynamoDB using multiple Indexes? - amazon-web-services

Question

I have an AWS DynamoDb cart table with the following item structure -
{
"cart_id": "5e4d0f9f-f08c-45ae-986a-f1b5ac7b7c13",
"user_id": 1234,
"type": "OTHER",
"currency": "INR",
"created_date": 132432423,
"expiry": 132432425,
"total_amount": 90000,
"total_quantity": 2,
"items": [
{
"amount": 90000,
"category": "Laptops",
"name": "Apple MacBook Pro",
"quantity": 1
}
]
}
-
{
"cart_id": "12340f9f-f08c-45ae-986a-f1b5ac7b1234",
"user_id": 1234,
"type": "SPECIAL",
"currency": "INR",
"created_date": 132432423,
"expiry": 132432425,
"total_amount": 1000,
"total_quantity": 2,
"items": [
{
"amount": 1000,
"category": "Special",
"name": "Special Item",
"quantity": 1
}
]
}
The table will have cart_id as Primary key,
user_id as an Index or GSI,
type as an Index or GSI.
I want to be able to query the cart table,
to find the items which have user_id = 1234 AND type != "SPECIAL".
I don't know if this means for the query -
--key-condition-expression "user_id = 1234 AND type != 'SPECIAL'"
I understand that an AWS DynamoDb table cannot be queried using multiple indexes at the same time,
I came across the following question, it has a similar use case and the answer is recommending creating a composite key,
Querying with multiple local Secondary Index Dynamodb
Does it mean that while putting a new item in the table,
I will need to maintain another column like user_id_type,
with its value as 1234SPECIAL and create an Index / GSI for user_id_type ?
Sample item structure -
{
"cart_id": "5e4d0f9f-f08c-45ae-986a-f1b5ac7b7c13",
"user_id": 1234,
"type": "OTHER",
"user_id_type" : "1234OTHER",
"currency": "INR",
"created_date": 132432423,
"expiry": 132432425,
"total_amount": 90000,
"total_quantity": 2,
"items": [
{
"amount": 90000,
"category": "Laptops",
"name": "Apple MacBook Pro",
"quantity": 1
}
]
}
References -
1. Querying with multiple local Secondary Index Dynamodb
2. Is there a way to query multiple hash keys in DynamoDB?

Answer 1

Your assumption is correct. Maybe you can add into that a delimitter field1_field2 or hash them if either of them is too big in size hashOfField1_hashOfField2
That mean spending some more processing power on your side, however. As DynamoDB does not natively support It.
Composite key in DynamoDB with more than 2 columns?
Dynamodb: query using more than two attributes
Additional info on your use case
KeyConditionExpression only allowed for the hash key.
You can put it in the FilterExpression
Why is there no **not equal** comparison in DynamoDB queries?

Answer 2

Does it mean that while putting a new item in the table,
I will need to maintain another column like user_id_type,
with its value as 1234SPECIAL and create an Index / GSI for user_id_type?
The answer is it depends on how many columns (dynamodb is schema-less, by a column I mean data field) you need and are you happy with 2 round trips to DB.
your query:
user_id = 1234 AND type != "SPECIAL"
1- if you need all information in the cart but you are happy with two round trips:
Solution: Create a GSI with user_id (HASH) and type (RANGE), then add cart_id (base table Hash key) as projection.
Explanation: so, you need one query on index table to get the cart_id given user_id and type
--key-condition-expression "user_id = 1234 AND type != 'SPECIAL'"
then you need to use cart_id(s) from the result and make another query to the base table
2- if you do not need all of cart information.
Solution: you need to create a GSI and make user_id HASH and type as RANGE and add more columns (columns you need) to projections.
Explanation: projection is additional columns you want to have in your index table. So, add some extra columns, which are more likely to be used as a result of the query, to avoid an extra round trip to the base table
Note: adding too many extra columns can double your costs, as any update on base table results in updates in GSI tables projection fields)
3- if you want just one round trip and you need all data
then you need to manage it by yourself and your suggestion can be applied

Answer 3

One possible answer is to create a single index with a sort key. Then you can do this:
{
TableName: "...",
IndexName: "UserIdAndTypeIndex",
KeyConditionExpression: "user_id = :user_id AND type != :type",
ExpressionAttributeValues: {
":user_id": 1234,
":type": "SPECIAL"
}
}

Answer 4

You can build GraphQL schema with AWS AppSync from your DynamoDB table and than query it in your app with GraphQL. Link