Fetch first five items from nested map DynamoDB NodeJS

Question

I have an object in a table like the following

```

{
  key: "apple",
  owners: { "Adam": "some info",
             "Eve": "some info",
             "Samuel": "some info"}

}
```

I want to be able to fetch the first five owners of the item with the key "apple".

I've tried everything but the maximum I can do is fetch the entire owners map from the item with the given key from DynamoDB then take the first five.

Now with time if the owners map contains a million or more owners I will need a lot of read units to complete the fetch for just the top five owners which I am trying to avoid.

Any help on the above would be appreciated.
node.js
amazon-dynamodb

Answer

The short answer is its not possible to do what you are trying, you must return the entire map.

Second, your read request unit will charge you for the entire read of the item, regardless which fields are returned.

Depending on your application needs, you may benefit from remodeling your schema:

| PK | SK | Other |
| --- | --- | --- |
| apple | OWNER#Adam | Data |
| apple | OWNER#Eve | Data |
| apple | OWNER#Samuel | Data |
| apple | OWNER#Lee | Data |
| orange | OWNER#Dave | Data |
| orange | OWNER#Matthew | Data |
| orange | OWNER#Sarah | Data |
| orange | OWNER#Ben | Data |

Now you can simply `Query` with `PK=apple`  & `Limit=5`

```
dynamodb.query({
    "TableName": 'Fruits',
    "KeyConditionExpression": `#pk = :val`,
    "ExpressionAttributeNames": {
        "#pk": "PK"
    },
    "ExpressionAttributeValues": {
        ":val": { "S": "apple" }
    },
    "Limit": 5
})
```

PK	SK	Other
apple	OWNER#Adam	Data
apple	OWNER#Eve	Data
apple	OWNER#Samuel	Data
apple	OWNER#Lee	Data
orange	OWNER#Dave	Data
orange	OWNER#Matthew	Data
orange	OWNER#Sarah	Data
orange	OWNER#Ben	Data

Fetch first five items from nested map DynamoDB NodeJS

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