Incrementing DynamoDB value using AWS SDK v3

Question

I'm attempting to migrate my v2 Lambdas to v3, and I'm having some trouble incrementing a value. Here's my v2 method:

  const params = {
    TableName: process.env.USER_TABLE_NAME!,
    Key: { UID },
    UpdateExpression: 'SET #numRatings = #numRatings + :increment',
    ExpressionAttributeNames: {
      '#numRatings': 'numRatings'
    },
    ExpressionAttributeValues: {
      ':increment': 1
    },
    ReturnValues: 'ALL_NEW'
  };

  return await DB.update(params).promise();

v3 method:

  const params = {
    TableName: process.env.USER_TABLE_NAME!,
    Key: {
      UID
    },
    UpdateExpression: 'set numRatings = numRatings + :increment',
    ExpressionAttributeValues: {
      ':increment': 1
    },
    ReturnValues: 'ALL_NEW'
  } as unknown as UpdateItemCommandInput;

  try {
    const response = await dbClient.send(new UpdateItemCommand(params));
    console.log('response', response);
  } catch (error) {
    console.error('error', error);
  }

I'm using TypeScript and VS Code gives this error:

Types of property 'Key' are incompatible.
    Type '{ UID: string; }' is not comparable to type '{ [key: string]: AttributeValue; }'.
      Property 'UID' is incompatible with index signature.
        Type 'string' is not comparable to type 'AttributeValue'

CloudWatch gives this unhelpful error:

Cannot read property '0' of undefined

I'm really confused as, as far as I can tell I have followed the documentation properly, their equivalent of "params" is defined as so:

export const params = {
  TableName: "TABLE_NAME",
  Key: {
    primaryKey: "VALUE_1", // For example, 'Season': 2.
    sortKey: "VALUE_2", // For example,  'Episode': 1; (only required if table has sort key).
  },
  // Define expressions for the new or updated attributes
  UpdateExpression: "set ATTRIBUTE_NAME_1 = :t, ATTRIBUTE_NAME_2 = :s", // For example, "'set Title = :t, Subtitle = :s'"
  ExpressionAttributeValues: {
    ":t": "NEW_ATTRIBUTE_VALUE_1", // For example ':t' : 'NEW_TITLE'
    ":s": "NEW_ATTRIBUTE_VALUE_2", // For example ':s' : 'NEW_SUBTITLE'
  },
  ReturnValues: "ALL_NEW"
};

My apologies if that's too many code examples but I wanted to be thorough. UID is a string. Thank you in advance for any help

Have you pinned down specifically which line is producing the error you described (just to rule out that it's not some external issue)? — Norman
– Norman, Commented Jan 21, 2022 at 0:14
@hunterhacker, the partition key is “UID”, ES6 allows for the key and value to be shortened to just the name of both if they’re the same alligator.io/js/object-property-shorthand-es6 — Jonathan
– Jonathan, Commented Jan 21, 2022 at 10:02
@Norman the track in AWS doesn’t refer to a specific line, but the only line it could possibly be is “const response = await dbClient.send(new UpdateItemCommand(params));” — Jonathan
– Jonathan, Commented Jan 21, 2022 at 10:03

Jonathan · Accepted Answer · 2022-01-21 13:39:37Z

2

Keys and ExpressionAttributeValues need their Dynamo type defined as so:

...
  Key: {
    UID: { S: UID }
  },
...
  ExpressionAttributeValues: {
    ':val': { N: '1' }
  },

answered Jan 21, 2022 at 13:39

Jonathan

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2 Comments

hunterhacker Over a year ago

Right. Notice how in this Key block there's both a name and a value for the partition key? In your sample there's just a value, no name. You may be thinking "Well the database knows the partition key name and there's no sort key so a simple value should work!" but you still need to specify it as a name-value pair.

Jonathan Over a year ago

Was battling prettier / ESLint to stop it from removing it but even “UID: UID” wasn’t working. The AWS SDK documentation should be updated to reference the requirement for the key type

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