How to query DynamoDB with any value in the sort key?

Question

I have a simple table with userId, pictureURL and a few other fields. I want to return all the fields with a certain userId but when I do

dynamodb.get({
  TableName: tableName,
  Key: {
    'userid': '39e1f6cb-22af-4f8c-adf5-xxxxxxxxxx'
  }
}, ...

I get The provided key element does not match the schema since it seems like it requires also the sort key. When I do

dynamodb.get({
  TableName: tableName,
  Key: {
    'userid': '39e1f6cb-22af-4f8c-adf5-xxxxxxxxxx',
    'pictureurl': '' // Or null
  }
}, ...

I get an error One or more parameter values were invalid: An AttributeValue may not contain an empty string

So how do I query for any value in the sort key?

jarmod · Accepted Answer · 2019-07-12 18:06:31Z

2

With the DynamoDB DocumentClient:

to query for a number of items, you use query
to get a single item, you use get

So, use query and use the KeyConditionExpression parameter to provide a specific value for the partition key. The query operation will return all of the items from the table (or index) with that partition key value.

Here's an example:

const AWS = require("aws-sdk");
AWS.config.update({region: 'us-east-1'});

const params = {
  TableName: tableName,
  KeyConditionExpression: '#userid = :userid',
  ExpressionAttributeNames: {
    '#userid': 'userid',
  },
  ExpressionAttributeValues: {
    ':userid': '39e1f6cb-22af-4f8c-adf5-xxxxxxxxxx',
  },
};

const dc = new AWS.DynamoDB.DocumentClient();

dc.query(params, (err, data) => {
  if (err) {
    console.log('Error', err);
  } else {
    for (const item of data.Items) {
      console.log('item:', item);
    };
  }
});

edited Jul 12, 2019 at 18:06

answered Jul 12, 2019 at 16:01

jarmod

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2 Comments

guzmonne Over a year ago

He might be referring to the AWS.DynamoDB.DocumentClient interface, which indeed exposes a get method.

guzmonne Over a year ago

I think it is essential to add that the query method only allows an equality check on the partition key, and equality, less/more, and begins_with queries on the sort key, and that's it.

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