DynamoDB Update Deep Nested Attributes

Question

I have the following data structure with multi-level Map columns/items:

```
{
"pk": {
    "S": "cf633075-e808-4e33-9fc1-08301b54384b"
},
"active": {
    "N": "1"
},
"delta": {
    "N": "-0.9371997798455771"
},
"dte": {
    "N": "0.01893752246685426"
},
"hedge_positions": {
  "M": {
    "151e9c9f-aa5d-4f5d-9826-74011da03137": {
      "M": {
        "active": {
          "N": "1"
        },
        ...
      }
    },
    "1bed59c9-6f73-48ae-8b65-62fd1f10ddad": {
      "M": {
        "active": {
          "N": "1"
        },
        ....
      }
    },
    "24cf6015-780e-408d-b0e1-935ae2c7199d": {
      "M": {
        "active": {
          "N": "1" //Update this to 0
        },
        ...
      }
    }
  }
}
```
I now wish to update the value of "active" for one of the "hedge_positions" to 0. The hedge_positions is a Map, containing unique Maps.
In Javascript, I have built the following update, but I am recieving the error "The provided expression refers to an attribute that does not exist in the item".

```
const AWS = require('aws-sdk');
const dynamoDb = new AWS.DynamoDB({region: process.env.AWS_REGION});

var hID = "24cf6015-780e-408d-b0e1-935ae2c7199d";

var params = {
            TableName: Positions,
            Key: {
                pk: {"S": positionId }
            },
            UpdateExpression: "SET #hp.#id.#a = :a",
            ExpressionAttributeValues: {":a": {"N": "0"}},
            ExpressionAttributeNames: {"#hp": "hedge_positions", "#id": hID, "#a": "active"}
};

await dynamoDb.updateItem(params).promise();
```
I believe this to be because I am not specifying that the "GUID" is itself a Map. I have tried to set the UpdateExpression to "SET #hp.#id.M.#a = :a" but to no avail. What have I set incorrectly in the UpdateExpression?

Answer

I tested this in my own account and it works with no issue, returning the NEW_IMAGE in the response to ensure the update was successful:

```
const AWS = require('aws-sdk');
const dynamoDb = new AWS.DynamoDB({region: 'eu-west-1'});

var hID = "24cf6015-780e-408d-b0e1-935ae2c7199d";

var params = {
    TableName: "cust1",
    Key: {
        pk: { "S": "123" },
        sk: { "S": "abc" }
    },
    UpdateExpression: "SET #hp.#id.#a = :a",
    ExpressionAttributeValues: { ":a": { "N": "0" } },
    ExpressionAttributeNames: { "#hp": "hedge_positions", "#id": hID, "#a": "active" }, 
    ReturnValues: "ALL_NEW"
};

dynamoDb.updateItem(params)
.promise()
.then(res=>console.log(JSON.stringify(res)))
.catch(err=>console.log(err));
```

Item before:
```
{
 "pk": "123",
 "sk": "abc",
 "active": 1,
 "delta": -0.9371997798455771,
 "dte": 0.01893752246685426,
 "hedge_positions": {
  "151e9c9f-aa5d-4f5d-9826-74011da03137": {
   "active": 1
  },
  "1bed59c9-6f73-48ae-8b65-62fd1f10ddad": {
   "active": 1
  },
  "24cf6015-780e-408d-b0e1-935ae2c7199d": {
   "active": 1
  }
 }
}
```

Item After:
```
{
 "pk": "123",
 "sk": "abc",
 "active": 1,
 "delta": -0.9371997798455771,
 "dte": 0.01893752246685426,
 "hedge_positions": {
  "151e9c9f-aa5d-4f5d-9826-74011da03137": {
   "active": 1
  },
  "1bed59c9-6f73-48ae-8b65-62fd1f10ddad": {
   "active": 1
  },
  "24cf6015-780e-408d-b0e1-935ae2c7199d": {
   "active": 0
  }
 }
}
```

DynamoDB Update Deep Nested Attributes

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