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Amazon DynamoDB
API Reference (API Version 2012-08-10)

ExpectedAttributeValue

Represents a condition to be compared with an attribute value. This condition can be used with DeleteItem, PutItem or UpdateItem operations; if the comparison evaluates to true, the operation succeeds; if not, the operation fails. You can use ExpectedAttributeValue in one of two different ways:

  • Use AttributeValueList to specify one or more values to compare against an attribute. Use ComparisonOperator to specify how you want to perform the comparison. If the comparison evaluates to true, then the conditional operation succeeds.

  • Use Value to specify a value that DynamoDB will compare against an attribute. If the values match, then ExpectedAttributeValue evaluates to true and the conditional operation succeeds. Optionally, you can also set Exists to false, indicating that you do not expect to find the attribute value in the table. In this case, the conditional operation succeeds only if the comparison evaluates to false.

Value and Exists are incompatible with AttributeValueList and ComparisonOperator. Note that if you use both sets of parameters at once, DynamoDB will return a ValidationException exception.

Contents

Note

In the following list, the required parameters are described first.

AttributeValueList

One or more values to evaluate against the supplied attribute. The number of values in the list depends on the ComparisonOperator being used.

For type Number, value comparisons are numeric.

String value comparisons for greater than, equals, or less than are based on ASCII character code values. For example, a is greater than A, and a is greater than B. For a list of code values, see http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters.

For Binary, DynamoDB treats each byte of the binary data as unsigned when it compares binary values.

For information on specifying data types in JSON, see JSON Data Format in the Amazon DynamoDB Developer Guide.

Type: array of AttributeValue objects

Required: No

ComparisonOperator

A comparator for evaluating attributes in the AttributeValueList. For example, equals, greater than, less than, etc.

The following comparison operators are available:

EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN

The following are descriptions of each comparison operator.

  • EQ : Equal. EQ is supported for all data types, including lists and maps.

    AttributeValueList can contain only one AttributeValue element of type String, Number, Binary, String Set, Number Set, or Binary Set. If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"}. Also, {"N":"6"} does not equal {"NS":["6", "2", "1"]}.

  • NE : Not equal. NE is supported for all data types, including lists and maps.

    AttributeValueList can contain only one AttributeValue of type String, Number, Binary, String Set, Number Set, or Binary Set. If an item contains an AttributeValue of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"}. Also, {"N":"6"} does not equal {"NS":["6", "2", "1"]}.

  • LE : Less than or equal.

    AttributeValueList can contain only one AttributeValue element of type String, Number, or Binary (not a set type). If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"}. Also, {"N":"6"} does not compare to {"NS":["6", "2", "1"]}.

  • LT : Less than.

    AttributeValueList can contain only one AttributeValue of type String, Number, or Binary (not a set type). If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"}. Also, {"N":"6"} does not compare to {"NS":["6", "2", "1"]}.

  • GE : Greater than or equal.

    AttributeValueList can contain only one AttributeValue element of type String, Number, or Binary (not a set type). If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"}. Also, {"N":"6"} does not compare to {"NS":["6", "2", "1"]}.

  • GT : Greater than.

    AttributeValueList can contain only one AttributeValue element of type String, Number, or Binary (not a set type). If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"}. Also, {"N":"6"} does not compare to {"NS":["6", "2", "1"]}.

  • NOT_NULL : The attribute exists. NOT_NULL is supported for all data types, including lists and maps.

    Note

    This operator tests for the existence of an attribute, not its data type. If the data type of attribute "a" is null, and you evaluate it using NOT_NULL, the result is a Boolean true. This result is because the attribute "a" exists; its data type is not relevant to the NOT_NULL comparison operator.

  • NULL : The attribute does not exist. NULL is supported for all data types, including lists and maps.

    Note

    This operator tests for the nonexistence of an attribute, not its data type. If the data type of attribute "a" is null, and you evaluate it using NULL, the result is a Boolean false. This is because the attribute "a" exists; its data type is not relevant to the NULL comparison operator.

  • CONTAINS : Checks for a subsequence, or value in a set.

    AttributeValueList can contain only one AttributeValue element of type String, Number, or Binary (not a set type). If the target attribute of the comparison is of type String, then the operator checks for a substring match. If the target attribute of the comparison is of type Binary, then the operator looks for a subsequence of the target that matches the input. If the target attribute of the comparison is a set ("SS", "NS", or "BS"), then the operator evaluates to true if it finds an exact match with any member of the set.

    CONTAINS is supported for lists: When evaluating "a CONTAINS b", "a" can be a list; however, "b" cannot be a set, a map, or a list.

  • NOT_CONTAINS : Checks for absence of a subsequence, or absence of a value in a set.

    AttributeValueList can contain only one AttributeValue element of type String, Number, or Binary (not a set type). If the target attribute of the comparison is a String, then the operator checks for the absence of a substring match. If the target attribute of the comparison is Binary, then the operator checks for the absence of a subsequence of the target that matches the input. If the target attribute of the comparison is a set ("SS", "NS", or "BS"), then the operator evaluates to true if it does not find an exact match with any member of the set.

    NOT_CONTAINS is supported for lists: When evaluating "a NOT CONTAINS b", "a" can be a list; however, "b" cannot be a set, a map, or a list.

  • BEGINS_WITH : Checks for a prefix.

    AttributeValueList can contain only one AttributeValue of type String or Binary (not a Number or a set type). The target attribute of the comparison must be of type String or Binary (not a Number or a set type).

  • IN : Checks for matching elements in a list.

    AttributeValueList can contain one or more AttributeValue elements of type String, Number, or Binary. These attributes are compared against an existing attribute of an item. If any elements of the input are equal to the item attribute, the expression evaluates to true.

  • BETWEEN : Greater than or equal to the first value, and less than or equal to the second value.

    AttributeValueList must contain two AttributeValue elements of the same type, either String, Number, or Binary (not a set type). A target attribute matches if the target value is greater than, or equal to, the first element and less than, or equal to, the second element. If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not compare to {"N":"6"}. Also, {"N":"6"} does not compare to {"NS":["6", "2", "1"]}

Type: String

Valid Values: EQ | NE | IN | LE | LT | GE | GT | BETWEEN | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH

Required: No

Exists

Causes DynamoDB to evaluate the value before attempting a conditional operation:

  • If Exists is true, DynamoDB will check to see if that attribute value already exists in the table. If it is found, then the operation succeeds. If it is not found, the operation fails with a ConditionalCheckFailedException.

  • If Exists is false, DynamoDB assumes that the attribute value does not exist in the table. If in fact the value does not exist, then the assumption is valid and the operation succeeds. If the value is found, despite the assumption that it does not exist, the operation fails with a ConditionalCheckFailedException.

The default setting for Exists is true. If you supply a Value all by itself, DynamoDB assumes the attribute exists: You don't have to set Exists to true, because it is implied.

DynamoDB returns a ValidationException if:

  • Exists is true but there is no Value to check. (You expect a value to exist, but don't specify what that value is.)

  • Exists is false but you also provide a Value. (You cannot expect an attribute to have a value, while also expecting it not to exist.)

Type: Boolean

Required: No

Value

Represents the data for the expected attribute.

Each attribute value is described as a name-value pair. The name is the data type, and the value is the data itself.

For more information, see Data Types in the Amazon DynamoDB Developer Guide.

Type: AttributeValue object

Required: No