DynamoDB: Query KeyConditionExpression (Guide w/ Code Examples)

The KeyConditionExpression parameter is used to specify the key condition for query operations. It should be a string that follows the syntax of a condition expression, and it should be specified using the attribute name and value placeholders (Attribute_name = :value).

The ExpressionAttributeValues parameter is used to provide the values for the placeholders in the KeyConditionExpression. The values should be passed in an object where the keys are the placeholder names.

Here's an example of how you might use the query method to retrieve items from a DynamoDB table where the partition key is userId and the sort key is timestamp:

const AWS = require('aws-sdk');
const dynamodb = new AWS.DynamoDB.DocumentClient();

const params = {
  TableName: 'myTable',
  KeyConditionExpression: 'userId = :userId and timestamp >= :startTimestamp',
  ExpressionAttributeValues: {
    ':userId': '123',
    ':startTimestamp': 1560934400
  }
};

dynamodb.query(params, (err, data) => {
  if (err) {
    console.log(err);
  } else {
    console.log(data);
  }
});