updateItem method

Future<UpdateItemOutput> updateItem({ required Map<String, AttributeValue> key, required String tableName, Map<String, AttributeValueUpdate>? attributeUpdates, String? conditionExpression, ConditionalOperator? conditionalOperator, Map<String, ExpectedAttributeValue>? expected, Map<String, String>? expressionAttributeNames, Map<String, AttributeValue>? expressionAttributeValues, ReturnConsumedCapacity? returnConsumedCapacity, ReturnItemCollectionMetrics? returnItemCollectionMetrics, ReturnValue? returnValues, String? updateExpression, })

Edits an existing item's attributes, or adds a new item to the table if it does not already exist. You can put, delete, or add attribute values. You can also perform a conditional update on an existing item (insert a new attribute name-value pair if it doesn't exist, or replace an existing name-value pair if it has certain expected attribute values).

You can also return the item's attribute values in the same UpdateItem operation using the ReturnValues parameter.

May throw ConditionalCheckFailedException. May throw ProvisionedThroughputExceededException. May throw ResourceNotFoundException. May throw ItemCollectionSizeLimitExceededException. May throw TransactionConflictException. May throw RequestLimitExceeded. May throw InternalServerError.

Parameter key : The primary key of the item to be updated. Each element consists of an attribute name and a value for that attribute.

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 item to update.

Parameter attributeUpdates : This is a legacy parameter. Use UpdateExpression instead. For more information, see AttributeUpdates in the Amazon DynamoDB Developer Guide.

Parameter conditionExpression : A condition that must be satisfied in order for a conditional update to succeed.

An expression can contain any of the following:

• Functions: attribute_exists | attribute_not_exists | attribute_type | contains | begins_with | size

  These function names are case-sensitive.

• Comparison operators: = | <> | < | > | <= | >= | BETWEEN | IN
• Logical operators: AND | OR | NOT

For more information about condition expressions, see Specifying Conditions in the Amazon DynamoDB Developer Guide.

Parameter conditionalOperator : This is a legacy parameter. Use ConditionExpression instead. For more information, see ConditionalOperator in the Amazon DynamoDB Developer Guide.

Parameter expected : This is a legacy parameter. Use ConditionExpression instead. For more information, see Expected in the Amazon DynamoDB Developer Guide.

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 about expression attribute names, see Specifying Item Attributes in the Amazon DynamoDB Developer Guide.

Parameter expressionAttributeValues : One or more values that can be substituted in an expression.

Use the : (colon) character in an expression to dereference an attribute value. For example, suppose that you wanted to check whether the value of the ProductStatus attribute was one of the following:

Available | Backordered | Discontinued

You would first need to specify ExpressionAttributeValues as follows:

{ ":avail":{"S":"Available"}, ":back":{"S":"Backordered"}, ":disc":{"S":"Discontinued"} }

You could then use these values in an expression, such as this:

ProductStatus IN (:avail, :back, :disc)

For more information on expression attribute values, see Condition Expressions in the Amazon DynamoDB Developer Guide.

Parameter returnItemCollectionMetrics : Determines whether item collection metrics are returned. If set to SIZE, the response includes statistics about item collections, if any, that were modified during the operation are returned in the response. If set to NONE (the default), no statistics are returned.

Parameter returnValues : Use ReturnValues if you want to get the item attributes as they appear before or after they are updated. For UpdateItem, the valid values are:

• NONE - If ReturnValues is not specified, or if its value is NONE, then nothing is returned. (This setting is the default for ReturnValues.)
• ALL_OLD - Returns all of the attributes of the item, as they appeared before the UpdateItem operation.
• UPDATED_OLD - Returns only the updated attributes, as they appeared before the UpdateItem operation.
• ALL_NEW - Returns all of the attributes of the item, as they appear after the UpdateItem operation.
• UPDATED_NEW - Returns only the updated attributes, as they appear after the UpdateItem operation.

There is no additional cost associated with requesting a return value aside from the small network and processing overhead of receiving a larger response. No read capacity units are consumed.

The values returned are strongly consistent.

Parameter updateExpression : An expression that defines one or more attributes to be updated, the action to be performed on them, and new values for them.

The following action values are available for UpdateExpression.

• SET - Adds one or more attributes and values to an item. If any of these attributes already exist, they are replaced by the new values. You can also use SET to add or subtract from an attribute that is of type Number. For example: SET myNum = myNum + :val

  SET supports the following functions:

  • if_not_exists (path, operand) - if the item does not contain an attribute at the specified path, then if_not_exists evaluates to operand; otherwise, it evaluates to path. You can use this function to avoid overwriting an attribute that may already be present in the item.
  • list_append (operand, operand) - evaluates to a list with a new element added to it. You can append the new element to the start or the end of the list by reversing the order of the operands.
  These function names are case-sensitive.
• REMOVE - Removes one or more attributes from an item.
• ADD - Adds the specified value to the item, if the attribute does not already exist. If the attribute does exist, then the behavior of ADD depends on the data type of the attribute:
  • If the existing attribute is a number, and if Value is also a number, then Value is mathematically added to the existing attribute. If Value is a negative number, then it is subtracted from the existing attribute.
  • If the existing data type is a set and if Value is also a set, then Value is added to the existing set. For example, if the attribute value is the set [1,2], and the ADD action specified [3], then the final attribute value is [1,2,3]. An error occurs if an ADD action is specified for a set attribute and the attribute type specified does not match the existing set type.

    Both sets must have the same primitive data type. For example, if the existing data type is a set of strings, the Value must also be a set of strings.

• DELETE - Deletes an element from a set.

  If a set of values is specified, then those values are subtracted from the old set. For example, if the attribute value was the set a,b,c and the DELETE action specifies a,c, then the final attribute value is b. Specifying an empty set is an error.

You can have many actions in a single expression, such as the following: SET a=:value1, b=:value2 DELETE :value3, :value4, :value5

For more information on update expressions, see Modifying Items and Attributes in the Amazon DynamoDB Developer Guide.

Implementation

Future<UpdateItemOutput> updateItem({
  required Map<String, AttributeValue> key,
  required String tableName,
  Map<String, AttributeValueUpdate>? attributeUpdates,
  String? conditionExpression,
  ConditionalOperator? conditionalOperator,
  Map<String, ExpectedAttributeValue>? expected,
  Map<String, String>? expressionAttributeNames,
  Map<String, AttributeValue>? expressionAttributeValues,
  ReturnConsumedCapacity? returnConsumedCapacity,
  ReturnItemCollectionMetrics? returnItemCollectionMetrics,
  ReturnValue? returnValues,
  String? updateExpression,
}) 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.UpdateItem'
  };
  final jsonResponse = await _protocol.send(
    method: 'POST',
    requestUri: '/',
    exceptionFnMap: _exceptionFns,
    // TODO queryParams
    headers: headers,
    payload: {
      'Key': key,
      'TableName': tableName,
      if (attributeUpdates != null) 'AttributeUpdates': attributeUpdates,
      if (conditionExpression != null)
        'ConditionExpression': conditionExpression,
      if (conditionalOperator != null)
        'ConditionalOperator': conditionalOperator.toValue(),
      if (expected != null) 'Expected': expected,
      if (expressionAttributeNames != null)
        'ExpressionAttributeNames': expressionAttributeNames,
      if (expressionAttributeValues != null)
        'ExpressionAttributeValues': expressionAttributeValues,
      if (returnConsumedCapacity != null)
        'ReturnConsumedCapacity': returnConsumedCapacity.toValue(),
      if (returnItemCollectionMetrics != null)
        'ReturnItemCollectionMetrics': returnItemCollectionMetrics.toValue(),
      if (returnValues != null) 'ReturnValues': returnValues.toValue(),
      if (updateExpression != null) 'UpdateExpression': updateExpression,
    },
  );

  return UpdateItemOutput.fromJson(jsonResponse.body);
}