getItem method

Future<GetItemOutput> getItem({ required Map<String, AttributeValue> key, required String tableName, List<String>? attributesToGet, bool? consistentRead, Map<String, String>? expressionAttributeNames, String? projectionExpression, ReturnConsumedCapacity? returnConsumedCapacity, })

The GetItem operation returns a set of attributes for the item with the given primary key. If there is no matching item, GetItem does not return any data and there will be no Item element in the response.

GetItem provides an eventually consistent read by default. If your application requires a strongly consistent read, set ConsistentRead to true. Although a strongly consistent read might take more time than an eventually consistent read, it always returns the last updated value.

May throw ProvisionedThroughputExceededException. May throw ResourceNotFoundException. May throw RequestLimitExceeded. May throw InternalServerError.

Parameter key : A map of attribute names to AttributeValue objects, representing the primary key of the item to retrieve.

For the primary key, you must provide all of the attributes. For example, with a simple primary key, you only need to provide a value for the partition key. For a composite primary key, you must provide values for both the partition key and the sort key.

Parameter tableName : The name of the table containing the requested item.

Parameter attributesToGet : This is a legacy parameter. Use ProjectionExpression instead. For more information, see AttributesToGet in the Amazon DynamoDB Developer Guide.

Parameter consistentRead : Determines the read consistency model: If set to true, then the operation uses strongly consistent reads; otherwise, the operation uses eventually consistent reads.

Parameter expressionAttributeNames : One or more substitution tokens for attribute names in an expression. The following are some use cases for using ExpressionAttributeNames:

• To access an attribute whose name conflicts with a DynamoDB reserved word.
• To create a placeholder for repeating occurrences of an attribute name in an expression.
• To prevent special characters in an attribute name from being misinterpreted in an expression.

Use the # character in an expression to dereference an attribute name. For example, consider the following attribute name:

• Percentile

The name of this attribute conflicts with a reserved word, so it cannot be used directly in an expression. (For the complete list of reserved words, see Reserved Words in the Amazon DynamoDB Developer Guide). To work around this, you could specify the following for ExpressionAttributeNames:

• {"#P":"Percentile"}

You could then use this substitution in an expression, as in this example:

• #P = :val

For more information on expression attribute names, see Specifying Item Attributes in the Amazon DynamoDB Developer Guide.

Parameter projectionExpression : A string that identifies one or more attributes to retrieve from the table. These attributes can include scalars, sets, or elements of a JSON document. The attributes in the expression must be separated by commas.

If no attribute names are specified, then all attributes are returned. If any of the requested attributes are not found, they do not appear in the result.

For more information, see Specifying Item Attributes in the Amazon DynamoDB Developer Guide.

Implementation

Future<GetItemOutput> getItem({
  required Map<String, AttributeValue> key,
  required String tableName,
  List<String>? attributesToGet,
  bool? consistentRead,
  Map<String, String>? expressionAttributeNames,
  String? projectionExpression,
  ReturnConsumedCapacity? returnConsumedCapacity,
}) async {
  ArgumentError.checkNotNull(key, 'key');
  ArgumentError.checkNotNull(tableName, 'tableName');
  _s.validateStringLength(
    'tableName',
    tableName,
    3,
    255,
    isRequired: true,
  );
  final headers = <String, String>{
    'Content-Type': 'application/x-amz-json-1.0',
    'X-Amz-Target': 'DynamoDB_20120810.GetItem'
  };
  final jsonResponse = await _protocol.send(
    method: 'POST',
    requestUri: '/',
    exceptionFnMap: _exceptionFns,
    // TODO queryParams
    headers: headers,
    payload: {
      'Key': key,
      'TableName': tableName,
      if (attributesToGet != null) 'AttributesToGet': attributesToGet,
      if (consistentRead != null) 'ConsistentRead': consistentRead,
      if (expressionAttributeNames != null)
        'ExpressionAttributeNames': expressionAttributeNames,
      if (projectionExpression != null)
        'ProjectionExpression': projectionExpression,
      if (returnConsumedCapacity != null)
        'ReturnConsumedCapacity': returnConsumedCapacity.toValue(),
    },
  );

  return GetItemOutput.fromJson(jsonResponse.body);
}