update_item(**kwargs)¶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.
See also: AWS API Documentation
Request Syntax
response = client.update_item(
TableName='string',
Key={
'string': {
'S': 'string',
'N': 'string',
'B': b'bytes',
'SS': [
'string',
],
'NS': [
'string',
],
'BS': [
b'bytes',
],
'M': {
'string': {'... recursive ...'}
},
'L': [
{'... recursive ...'},
],
'NULL': True|False,
'BOOL': True|False
}
},
AttributeUpdates={
'string': {
'Value': {
'S': 'string',
'N': 'string',
'B': b'bytes',
'SS': [
'string',
],
'NS': [
'string',
],
'BS': [
b'bytes',
],
'M': {
'string': {'... recursive ...'}
},
'L': [
{'... recursive ...'},
],
'NULL': True|False,
'BOOL': True|False
},
'Action': 'ADD'|'PUT'|'DELETE'
}
},
Expected={
'string': {
'Value': {
'S': 'string',
'N': 'string',
'B': b'bytes',
'SS': [
'string',
],
'NS': [
'string',
],
'BS': [
b'bytes',
],
'M': {
'string': {'... recursive ...'}
},
'L': [
{'... recursive ...'},
],
'NULL': True|False,
'BOOL': True|False
},
'Exists': True|False,
'ComparisonOperator': 'EQ'|'NE'|'IN'|'LE'|'LT'|'GE'|'GT'|'BETWEEN'|'NOT_NULL'|'NULL'|'CONTAINS'|'NOT_CONTAINS'|'BEGINS_WITH',
'AttributeValueList': [
{
'S': 'string',
'N': 'string',
'B': b'bytes',
'SS': [
'string',
],
'NS': [
'string',
],
'BS': [
b'bytes',
],
'M': {
'string': {'... recursive ...'}
},
'L': [
{'... recursive ...'},
],
'NULL': True|False,
'BOOL': True|False
},
]
}
},
ConditionalOperator='AND'|'OR',
ReturnValues='NONE'|'ALL_OLD'|'UPDATED_OLD'|'ALL_NEW'|'UPDATED_NEW',
ReturnConsumedCapacity='INDEXES'|'TOTAL'|'NONE',
ReturnItemCollectionMetrics='SIZE'|'NONE',
UpdateExpression='string',
ConditionExpression='string',
ExpressionAttributeNames={
'string': 'string'
},
ExpressionAttributeValues={
'string': {
'S': 'string',
'N': 'string',
'B': b'bytes',
'SS': [
'string',
],
'NS': [
'string',
],
'BS': [
b'bytes',
],
'M': {
'string': {'... recursive ...'}
},
'L': [
{'... recursive ...'},
],
'NULL': True|False,
'BOOL': True|False
}
}
)
[REQUIRED]
The name of the table containing the item to update.
[REQUIRED]
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.
Represents the data for an 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 .
An attribute of type String. For example:
"S": "Hello"
An attribute of type Number. For example:
"N": "123.45"
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
An attribute of type Binary. For example:
"B": "dGhpcyB0ZXh0IGlzIGJhc2U2NC1lbmNvZGVk"
An attribute of type String Set. For example:
"SS": ["Giraffe", "Hippo" ,"Zebra"]
An attribute of type Number Set. For example:
"NS": ["42.2", "-19", "7.5", "3.14"]
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
An attribute of type Binary Set. For example:
"BS": ["U3Vubnk=", "UmFpbnk=", "U25vd3k="]
An attribute of type Map. For example:
"M": {"Name": {"S": "Joe"}, "Age": {"N": "35"}}
Represents the data for an 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 .
An attribute of type List. For example:
"L": [ {"S": "Cookies"} , {"S": "Coffee"}, {"N": "3.14159"}]
Represents the data for an 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 .
An attribute of type Null. For example:
"NULL": true
An attribute of type Boolean. For example:
"BOOL": true
This is a legacy parameter. Use UpdateExpression instead. For more information, see AttributeUpdates in the Amazon DynamoDB Developer Guide .
For the UpdateItem operation, represents the attributes to be modified, the action to perform on each, and the new value for each.
Note
You cannot use UpdateItem to update any primary key attributes. Instead, you will need to delete the item, and then use PutItem to create a new item with new attributes.
Attribute values cannot be null; string and binary type attributes must have lengths greater than zero; and set type attributes must not be empty. Requests with empty values will be rejected with a ValidationException exception.
Represents the data for an 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 .
An attribute of type String. For example:
"S": "Hello"
An attribute of type Number. For example:
"N": "123.45"
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
An attribute of type Binary. For example:
"B": "dGhpcyB0ZXh0IGlzIGJhc2U2NC1lbmNvZGVk"
An attribute of type String Set. For example:
"SS": ["Giraffe", "Hippo" ,"Zebra"]
An attribute of type Number Set. For example:
"NS": ["42.2", "-19", "7.5", "3.14"]
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
An attribute of type Binary Set. For example:
"BS": ["U3Vubnk=", "UmFpbnk=", "U25vd3k="]
An attribute of type Map. For example:
"M": {"Name": {"S": "Joe"}, "Age": {"N": "35"}}
Represents the data for an 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 .
An attribute of type List. For example:
"L": [ {"S": "Cookies"} , {"S": "Coffee"}, {"N": "3.14159"}]
Represents the data for an 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 .
An attribute of type Null. For example:
"NULL": true
An attribute of type Boolean. For example:
"BOOL": true
Specifies how to perform the update. Valid values are PUT (default), DELETE , and ADD . The behavior depends on whether the specified primary key already exists in the table.
If an item with the specified Key is found in the table:
PUT - Adds the specified attribute to the item. If the attribute already exists, it is replaced by the new value.DELETE - If no value is specified, the attribute and its value are removed from the item. The data type of the specified value must match the existing value's data type. 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 specified [a,c] , then the final attribute value would be [b] . Specifying an empty set is an error.ADD - If the attribute does not already exist, then the attribute and its values are added to the item. If the attribute does exist, then the behavior of ADD depends on the data type of the attribute:Value is also a number, then the Value is mathematically added to the existing attribute. If Value is a negative number, then it is subtracted from the existing attribute.Note
If you use ADD to increment or decrement a number value for an item that doesn't exist before the update, DynamoDB uses 0 as the initial value. In addition, if you use ADD to update an existing item, and intend to increment or decrement an attribute value which does not yet exist, DynamoDB uses 0 as the initial value. For example, suppose that the item you want to update does not yet have an attribute named itemcount , but you decide to ADD the number 3 to this attribute anyway, even though it currently does not exist. DynamoDB will create the itemcount attribute, set its initial value to 0 , and finally add 3 to it. The result will be a new itemcount attribute in the item, with a value of 3 .
Value is also a set, then the Value is added to the existing set. (This is a set operation, not mathematical addition.) For example, if the attribute value was the set [1,2] , and the ADD action specified [3] , then the final attribute value would be [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. The same holds true for number sets and binary sets.This action is only valid for an existing attribute whose data type is number or is a set. Do not use ADD for any other data types.
If no item with the specified Key is found:
PUT - DynamoDB creates a new item with the specified primary key, and then adds the attribute.DELETE - Nothing happens; there is no attribute to delete.ADD - DynamoDB creates a new item with the supplied primary key and number (or set) for the attribute value. The only data types allowed are number, number set, string set or binary set.This is a legacy parameter. Use ConditionExpression instead. For more information, see Expected in the Amazon DynamoDB Developer Guide .
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:
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.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.ValueandExistsare incompatible withAttributeValueListandComparisonOperator. Note that if you use both sets of parameters at once, DynamoDB will return aValidationExceptionexception.
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 .
An attribute of type String. For example:
"S": "Hello"
An attribute of type Number. For example:
"N": "123.45"
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
An attribute of type Binary. For example:
"B": "dGhpcyB0ZXh0IGlzIGJhc2U2NC1lbmNvZGVk"
An attribute of type String Set. For example:
"SS": ["Giraffe", "Hippo" ,"Zebra"]
An attribute of type Number Set. For example:
"NS": ["42.2", "-19", "7.5", "3.14"]
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
An attribute of type Binary Set. For example:
"BS": ["U3Vubnk=", "UmFpbnk=", "U25vd3k="]
An attribute of type Map. For example:
"M": {"Name": {"S": "Joe"}, "Age": {"N": "35"}}
Represents the data for an 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 .
An attribute of type List. For example:
"L": [ {"S": "Cookies"} , {"S": "Coffee"}, {"N": "3.14159"}]
Represents the data for an 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 .
An attribute of type Null. For example:
"NULL": true
An attribute of type Boolean. For example:
"BOOL": true
Causes DynamoDB to evaluate the value before attempting a conditional operation:
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 ConditionCheckFailedException .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 ConditionCheckFailedException .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.)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"]}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 .
Represents the data for an 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 .
An attribute of type String. For example:
"S": "Hello"
An attribute of type Number. For example:
"N": "123.45"
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
An attribute of type Binary. For example:
"B": "dGhpcyB0ZXh0IGlzIGJhc2U2NC1lbmNvZGVk"
An attribute of type String Set. For example:
"SS": ["Giraffe", "Hippo" ,"Zebra"]
An attribute of type Number Set. For example:
"NS": ["42.2", "-19", "7.5", "3.14"]
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
An attribute of type Binary Set. For example:
"BS": ["U3Vubnk=", "UmFpbnk=", "U25vd3k="]
An attribute of type Map. For example:
"M": {"Name": {"S": "Joe"}, "Age": {"N": "35"}}
Represents the data for an 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 .
An attribute of type List. For example:
"L": [ {"S": "Cookies"} , {"S": "Coffee"}, {"N": "3.14159"}]
Represents the data for an 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 .
An attribute of type Null. For example:
"NULL": true
An attribute of type Boolean. For example:
"BOOL": true
ConditionExpression instead. For more information, see ConditionalOperator in the Amazon DynamoDB Developer Guide .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.
Determines the level of detail about either provisioned or on-demand throughput consumption that is returned in the response:
INDEXES - The response includes the aggregate ConsumedCapacity for the operation, together with ConsumedCapacity for each table and secondary index that was accessed. Note that some operations, such as GetItem and BatchGetItem , do not access any indexes at all. In these cases, specifying INDEXES will only return ConsumedCapacity information for table(s).TOTAL - The response includes only the aggregate ConsumedCapacity for the operation.NONE - No ConsumedCapacity details are included in the response.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.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: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.Note
If you use ADD to increment or decrement a number value for an item that doesn't exist before the update, DynamoDB uses 0 as the initial value. Similarly, if you use ADD for an existing item to increment or decrement an attribute value that doesn't exist before the update, DynamoDB uses 0 as the initial value. For example, suppose that the item you want to update doesn't have an attribute named itemcount , but you decide to ADD the number 3 to this attribute anyway. DynamoDB will create the itemcount attribute, set its initial value to 0 , and finally add 3 to it. The result will be a new itemcount attribute in the item, with a value of 3 .
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.Warning
The ADD action only supports Number and set data types. In addition, ADD can only be used on top-level attributes, not nested attributes.
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.Warning
The DELETE action only supports set data types. In addition, DELETE can only be used on top-level attributes, not nested attributes.
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 .
A condition that must be satisfied in order for a conditional update to succeed.
An expression can contain any of the following:
attribute_exists | attribute_not_exists | attribute_type | contains | begins_with | size These function names are case-sensitive.= | <> | < | > | <= | >= | BETWEEN | INAND | OR | NOTFor more information about condition expressions, see Specifying Conditions in the Amazon DynamoDB Developer Guide .
One or more substitution tokens for attribute names in an expression. The following are some use cases for using ExpressionAttributeNames :
Use the # character in an expression to dereference an attribute name. For example, consider the following attribute name:
PercentileThe 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 = :valNote
Tokens that begin with the : character are expression attribute values , which are placeholders for the actual value at runtime.
For more information about expression attribute names, see Specifying Item Attributes in the Amazon DynamoDB Developer Guide .
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 .
Represents the data for an 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 .
An attribute of type String. For example:
"S": "Hello"
An attribute of type Number. For example:
"N": "123.45"
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
An attribute of type Binary. For example:
"B": "dGhpcyB0ZXh0IGlzIGJhc2U2NC1lbmNvZGVk"
An attribute of type String Set. For example:
"SS": ["Giraffe", "Hippo" ,"Zebra"]
An attribute of type Number Set. For example:
"NS": ["42.2", "-19", "7.5", "3.14"]
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
An attribute of type Binary Set. For example:
"BS": ["U3Vubnk=", "UmFpbnk=", "U25vd3k="]
An attribute of type Map. For example:
"M": {"Name": {"S": "Joe"}, "Age": {"N": "35"}}
Represents the data for an 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 .
An attribute of type List. For example:
"L": [ {"S": "Cookies"} , {"S": "Coffee"}, {"N": "3.14159"}]
Represents the data for an 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 .
An attribute of type Null. For example:
"NULL": true
An attribute of type Boolean. For example:
"BOOL": true
dict
Response Syntax
{
'Attributes': {
'string': {
'S': 'string',
'N': 'string',
'B': b'bytes',
'SS': [
'string',
],
'NS': [
'string',
],
'BS': [
b'bytes',
],
'M': {
'string': {'... recursive ...'}
},
'L': [
{'... recursive ...'},
],
'NULL': True|False,
'BOOL': True|False
}
},
'ConsumedCapacity': {
'TableName': 'string',
'CapacityUnits': 123.0,
'ReadCapacityUnits': 123.0,
'WriteCapacityUnits': 123.0,
'Table': {
'ReadCapacityUnits': 123.0,
'WriteCapacityUnits': 123.0,
'CapacityUnits': 123.0
},
'LocalSecondaryIndexes': {
'string': {
'ReadCapacityUnits': 123.0,
'WriteCapacityUnits': 123.0,
'CapacityUnits': 123.0
}
},
'GlobalSecondaryIndexes': {
'string': {
'ReadCapacityUnits': 123.0,
'WriteCapacityUnits': 123.0,
'CapacityUnits': 123.0
}
}
},
'ItemCollectionMetrics': {
'ItemCollectionKey': {
'string': {
'S': 'string',
'N': 'string',
'B': b'bytes',
'SS': [
'string',
],
'NS': [
'string',
],
'BS': [
b'bytes',
],
'M': {
'string': {'... recursive ...'}
},
'L': [
{'... recursive ...'},
],
'NULL': True|False,
'BOOL': True|False
}
},
'SizeEstimateRangeGB': [
123.0,
]
}
}
Response Structure
(dict) --
Represents the output of an UpdateItem operation.
Attributes (dict) --
A map of attribute values as they appear before or after the UpdateItem operation, as determined by the ReturnValues parameter.
The Attributes map is only present if ReturnValues was specified as something other than NONE in the request. Each element represents one attribute.
(string) --
(dict) --
Represents the data for an 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 .
S (string) --
An attribute of type String. For example:
"S": "Hello"
N (string) --
An attribute of type Number. For example:
"N": "123.45"
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
B (bytes) --
An attribute of type Binary. For example:
"B": "dGhpcyB0ZXh0IGlzIGJhc2U2NC1lbmNvZGVk"
SS (list) --
An attribute of type String Set. For example:
"SS": ["Giraffe", "Hippo" ,"Zebra"]
NS (list) --
An attribute of type Number Set. For example:
"NS": ["42.2", "-19", "7.5", "3.14"]
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
BS (list) --
An attribute of type Binary Set. For example:
"BS": ["U3Vubnk=", "UmFpbnk=", "U25vd3k="]
M (dict) --
An attribute of type Map. For example:
"M": {"Name": {"S": "Joe"}, "Age": {"N": "35"}}
(string) --
(dict) --
Represents the data for an 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 .
L (list) --
An attribute of type List. For example:
"L": [ {"S": "Cookies"} , {"S": "Coffee"}, {"N": "3.14159"}]
(dict) --
Represents the data for an 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 .
NULL (boolean) --
An attribute of type Null. For example:
"NULL": true
BOOL (boolean) --
An attribute of type Boolean. For example:
"BOOL": true
ConsumedCapacity (dict) --
The capacity units consumed by the UpdateItem operation. The data returned includes the total provisioned throughput consumed, along with statistics for the table and any indexes involved in the operation. ConsumedCapacity is only returned if the ReturnConsumedCapacity parameter was specified. For more information, see Provisioned Throughput in the Amazon DynamoDB Developer Guide .
TableName (string) --
The name of the table that was affected by the operation.
CapacityUnits (float) --
The total number of capacity units consumed by the operation.
ReadCapacityUnits (float) --
The total number of read capacity units consumed by the operation.
WriteCapacityUnits (float) --
The total number of write capacity units consumed by the operation.
Table (dict) --
The amount of throughput consumed on the table affected by the operation.
ReadCapacityUnits (float) --
The total number of read capacity units consumed on a table or an index.
WriteCapacityUnits (float) --
The total number of write capacity units consumed on a table or an index.
CapacityUnits (float) --
The total number of capacity units consumed on a table or an index.
LocalSecondaryIndexes (dict) --
The amount of throughput consumed on each local index affected by the operation.
(string) --
(dict) --
Represents the amount of provisioned throughput capacity consumed on a table or an index.
ReadCapacityUnits (float) --
The total number of read capacity units consumed on a table or an index.
WriteCapacityUnits (float) --
The total number of write capacity units consumed on a table or an index.
CapacityUnits (float) --
The total number of capacity units consumed on a table or an index.
GlobalSecondaryIndexes (dict) --
The amount of throughput consumed on each global index affected by the operation.
(string) --
(dict) --
Represents the amount of provisioned throughput capacity consumed on a table or an index.
ReadCapacityUnits (float) --
The total number of read capacity units consumed on a table or an index.
WriteCapacityUnits (float) --
The total number of write capacity units consumed on a table or an index.
CapacityUnits (float) --
The total number of capacity units consumed on a table or an index.
ItemCollectionMetrics (dict) --
Information about item collections, if any, that were affected by the UpdateItem operation. ItemCollectionMetrics is only returned if the ReturnItemCollectionMetrics parameter was specified. If the table does not have any local secondary indexes, this information is not returned in the response.
Each ItemCollectionMetrics element consists of:
ItemCollectionKey - The partition key value of the item collection. This is the same as the partition key value of the item itself.SizeEstimateRangeGB - An estimate of item collection size, in gigabytes. This value is a two-element array containing a lower bound and an upper bound for the estimate. The estimate includes the size of all the items in the table, plus the size of all attributes projected into all of the local secondary indexes on that table. Use this estimate to measure whether a local secondary index is approaching its size limit. The estimate is subject to change over time; therefore, do not rely on the precision or accuracy of the estimate.ItemCollectionKey (dict) --
The partition key value of the item collection. This value is the same as the partition key value of the item.
(string) --
(dict) --
Represents the data for an 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 .
S (string) --
An attribute of type String. For example:
"S": "Hello"
N (string) --
An attribute of type Number. For example:
"N": "123.45"
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
B (bytes) --
An attribute of type Binary. For example:
"B": "dGhpcyB0ZXh0IGlzIGJhc2U2NC1lbmNvZGVk"
SS (list) --
An attribute of type String Set. For example:
"SS": ["Giraffe", "Hippo" ,"Zebra"]
NS (list) --
An attribute of type Number Set. For example:
"NS": ["42.2", "-19", "7.5", "3.14"]
Numbers are sent across the network to DynamoDB as strings, to maximize compatibility across languages and libraries. However, DynamoDB treats them as number type attributes for mathematical operations.
BS (list) --
An attribute of type Binary Set. For example:
"BS": ["U3Vubnk=", "UmFpbnk=", "U25vd3k="]
M (dict) --
An attribute of type Map. For example:
"M": {"Name": {"S": "Joe"}, "Age": {"N": "35"}}
(string) --
(dict) --
Represents the data for an 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 .
L (list) --
An attribute of type List. For example:
"L": [ {"S": "Cookies"} , {"S": "Coffee"}, {"N": "3.14159"}]
(dict) --
Represents the data for an 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 .
NULL (boolean) --
An attribute of type Null. For example:
"NULL": true
BOOL (boolean) --
An attribute of type Boolean. For example:
"BOOL": true
SizeEstimateRangeGB (list) --
An estimate of item collection size, in gigabytes. This value is a two-element array containing a lower bound and an upper bound for the estimate. The estimate includes the size of all the items in the table, plus the size of all attributes projected into all of the local secondary indexes on that table. Use this estimate to measure whether a local secondary index is approaching its size limit.
The estimate is subject to change over time; therefore, do not rely on the precision or accuracy of the estimate.
Exceptions
DynamoDB.Client.exceptions.ConditionalCheckFailedExceptionDynamoDB.Client.exceptions.ProvisionedThroughputExceededExceptionDynamoDB.Client.exceptions.ResourceNotFoundExceptionDynamoDB.Client.exceptions.ItemCollectionSizeLimitExceededExceptionDynamoDB.Client.exceptions.TransactionConflictExceptionDynamoDB.Client.exceptions.RequestLimitExceededDynamoDB.Client.exceptions.InternalServerErrorExamples
This example updates an item in the Music table. It adds a new attribute (Year) and modifies the AlbumTitle attribute. All of the attributes in the item, as they appear after the update, are returned in the response.
response = client.update_item(
ExpressionAttributeNames={
'#AT': 'AlbumTitle',
'#Y': 'Year',
},
ExpressionAttributeValues={
':t': {
'S': 'Louder Than Ever',
},
':y': {
'N': '2015',
},
},
Key={
'Artist': {
'S': 'Acme Band',
},
'SongTitle': {
'S': 'Happy Day',
},
},
ReturnValues='ALL_NEW',
TableName='Music',
UpdateExpression='SET #Y = :y, #AT = :t',
)
print(response)
Expected Output:
{
'Attributes': {
'AlbumTitle': {
'S': 'Louder Than Ever',
},
'Artist': {
'S': 'Acme Band',
},
'SongTitle': {
'S': 'Happy Day',
},
'Year': {
'N': '2015',
},
},
'ResponseMetadata': {
'...': '...',
},
}