How to fix ValidationException: The provided key element does not match the schema in DynamoDB

# Describe table to see key schema
aws dynamodb describe-table --table-name YourTableName --region us-east-1

"KeySchema": [
  {
    "AttributeName": "userId",
    "KeyType": "HASH"  // This is the partition key
  },
  {
    "AttributeName": "timestamp",
    "KeyType": "RANGE"  // This is the sort key (if present)
  }
]

"AttributeDefinitions": [
  {
    "AttributeName": "userId",
    "AttributeType": "S"  // S = String, N = Number, B = Binary
  },
  {
    "AttributeName": "timestamp",
    "AttributeType": "N"
  }
]

import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocumentClient, GetCommand } from '@aws-sdk/lib-dynamodb';

const client = new DynamoDBClient({ region: 'us-east-1' });
const docClient = DynamoDBDocumentClient.from(client);

// Use native JavaScript types for keys
const result = await docClient.send(new GetCommand({
  TableName: 'YourTableName',
  Key: {
    userId: 'user123',      // String - native format
    timestamp: 1640000000   // Number - native format
  }
}));

import { DynamoDBClient, GetItemCommand } from '@aws-sdk/client-dynamodb';

const client = new DynamoDBClient({ region: 'us-east-1' });

// Use DynamoDB AttributeValue format for keys
const result = await client.send(new GetItemCommand({
  TableName: 'YourTableName',
  Key: {
    userId: { S: 'user123' },        // S for String
    timestamp: { N: '1640000000' }   // N for Number
  }
}));

# Low-level format (must use for CLI)
aws dynamodb get-item \
  --table-name YourTableName \
  --key '{"userId": {"S": "user123"}, "timestamp": {"N": "1640000000"}}' \
  --region us-east-1

const docClient = DynamoDBDocumentClient.from(client);

// Correct - both partition and sort key provided
await docClient.send(new GetCommand({
  TableName: 'YourTableName',
  Key: {
    userId: 'user123',      // Partition key
    timestamp: 1640000000   // Sort key
  }
}));

// This will fail with "key element does not match schema"
await docClient.send(new GetCommand({
  TableName: 'YourTableName',
  Key: {
    userId: 'user123'  // Missing timestamp sort key
  }
}));

// Correct - Query with only partition key (returns multiple items)
const result = await docClient.send(new QueryCommand({
  TableName: 'YourTableName',
  KeyConditionExpression: 'userId = :userId',
  ExpressionAttributeValues: {
    ':userId': 'user123'
  }
}));

// If your table schema defines:
// KeySchema: [{ AttributeName: "userId", KeyType: "HASH" }]

const docClient = DynamoDBDocumentClient.from(client);

// Correct - exact match
await docClient.send(new GetCommand({
  TableName: 'YourTableName',
  Key: {
    userId: 'user123'  // Matches "userId" exactly
  }
}));

// Incorrect - case mismatch
await docClient.send(new GetCommand({
  TableName: 'YourTableName',
  Key: {
    UserID: 'user123'  // Will fail - doesn't match "userId"
  }
}));

// Incorrect - typo
await docClient.send(new GetCommand({
  TableName: 'YourTableName',
  Key: {
    user_id: 'user123'  // Will fail - doesn't match "userId"
  }
}));

// Table schema has:
// partition key: accountId (type: N - Number)
// sort key: timestamp (type: S - String)

const docClient = DynamoDBDocumentClient.from(client);

// Correct - correct data types
await docClient.send(new GetCommand({
  TableName: 'YourTableName',
  Key: {
    accountId: 12345,        // Number (matches schema type N)
    timestamp: '2024-01-15'  // String (matches schema type S)
  }
}));

// Incorrect - wrong data type for accountId
await docClient.send(new GetCommand({
  TableName: 'YourTableName',
  Key: {
    accountId: '12345',      // String - doesn't match Number schema
    timestamp: '2024-01-15'
  }
}));

const accountIdFromAPI = '12345'; // String from API
const docClient = DynamoDBDocumentClient.from(client);

await docClient.send(new GetCommand({
  TableName: 'YourTableName',
  Key: {
    accountId: parseInt(accountIdFromAPI), // Convert to Number
    timestamp: '2024-01-15'
  }
}));

# Test with low-level format
aws dynamodb get-item \
  --table-name YourTableName \
  --key '{"userId": {"S": "user123"}, "timestamp": {"N": "1640000000"}}' \
  --region us-east-1

# If this succeeds, the issue is likely in your SDK client code
# If this fails, the issue is in your key specification