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

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.

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.

Request Syntax

{
    "AttributesToGet": [
        "string"
    ],
    "ConsistentRead": "boolean",
    "ExpressionAttributeNames": 
        {
            "string" :
                "string"
        },
    "Key": 
        {
            "string" :
                {
                    "B": "blob",
                    "BOOL": "boolean",
                    "BS": [
                        "blob"
                    ],
                    "L": [
                        AttributeValue
                    ],
                    "M": 
                        {
                            "string" :
                                AttributeValue
                        },
                    "N": "string",
                    "NS": [
                        "string"
                    ],
                    "NULL": "boolean",
                    "S": "string",
                    "SS": [
                        "string"
                    ]
                }
        },
    "ProjectionExpression": "string",
    "ReturnConsumedCapacity": "string",
    "TableName": "string"
}
			

Request Parameters

The request accepts the following data in JSON format.

Note

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

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 hash type primary key, you only need to provide the hash attribute. For a hash-and-range type primary key, you must provide both the hash attribute and the range attribute.

Type: String to AttributeValue object map

Required: Yes

TableName

The name of the table containing the requested item.

Type: String

Length constraints: Minimum length of 3. Maximum length of 255.

Required: Yes

AttributesToGet

Important

This is a legacy parameter, for backward compatibility. New applications should use ProjectionExpression instead. Do not combine legacy parameters and expression parameters in a single API call; otherwise, DynamoDB will return a ValidationException exception.

This parameter allows you to retrieve attributes of type List or Map; however, it cannot retrieve individual elements within a List or a Map.

The names of one or more attributes to retrieve. If no attribute names are provided, then all attributes will be returned. If any of the requested attributes are not found, they will not appear in the result.

Note that AttributesToGet has no effect on provisioned throughput consumption. DynamoDB determines capacity units consumed based on item size, not on the amount of data that is returned to an application.

Type: array of Strings

Length constraints: Minimum of 1 item(s) in the list.

Required: No

ConsistentRead

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

Type: Boolean

Required: No

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

Note

Tokens that begin with the : character are expression attribute values, which are placeholders for the actual value at runtime.

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

Type: String to String map

Required: No

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 will be returned. If any of the requested attributes are not found, they will not appear in the result.

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

Note

ProjectionExpression replaces the legacy AttributesToGet parameter.

Type: String

Required: No

ReturnConsumedCapacity

Determines the level of detail about provisioned 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.

Type: String

Valid Values: INDEXES | TOTAL | NONE

Required: No

Response Syntax

{
    "ConsumedCapacity": {
        "CapacityUnits": "number",
        "GlobalSecondaryIndexes": 
            {
                "string" :
                    {
                        "CapacityUnits": "number"
                    }
            },
        "LocalSecondaryIndexes": 
            {
                "string" :
                    {
                        "CapacityUnits": "number"
                    }
            },
        "Table": {
            "CapacityUnits": "number"
        },
        "TableName": "string"
    },
    "Item": 
        {
            "string" :
                {
                    "B": "blob",
                    "BOOL": "boolean",
                    "BS": [
                        "blob"
                    ],
                    "L": [
                        AttributeValue
                    ],
                    "M": 
                        {
                            "string" :
                                AttributeValue
                        },
                    "N": "string",
                    "NS": [
                        "string"
                    ],
                    "NULL": "boolean",
                    "S": "string",
                    "SS": [
                        "string"
                    ]
                }
        }
}
			

Response Elements

The following data is returned in JSON format by the service.

ConsumedCapacity

The capacity units consumed by an 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 request asked for it. For more information, see Provisioned Throughput in the Amazon DynamoDB Developer Guide.

Type: ConsumedCapacity object

Item

A map of attribute names to AttributeValue objects, as specified by AttributesToGet.

Type: String to AttributeValue object map

Errors

For information about the errors that are common to all actions, see Common Errors.

InternalServerError

An error occurred on the server side.

HTTP Status Code: 500

ProvisionedThroughputExceededException

The request rate is too high, or the request is too large, for the available throughput to accommodate. The AWS SDKs automatically retry requests that receive this exception; therefore, your request will eventually succeed, unless the request is too large or your retry queue is too large to finish. Reduce the frequency of requests by using the strategies listed in Error Retries and Exponential Backoff in the Amazon DynamoDB Developer Guide.

HTTP Status Code: 400

ResourceNotFoundException

The operation tried to access a nonexistent table or index. The resource might not be specified correctly, or its status might not be ACTIVE.

HTTP Status Code: 400

Examples

Retrieve Item Attributes

The following example retrieves three attributes from the Thread table. In the response, the ConsumedCapacityUnits value is 1, because ConsistentRead is set to true. If ConsistentRead had been set to false (or not specified) for the same request, an eventually consistent read would have been used and ConsumedCapacityUnits would have been 0.5.

Sample Request

POST / HTTP/1.1
Host: dynamodb.<region>.<domain>;
X-Amz-Date: <Date>
Authorization: AWS4-HMAC-SHA256 Credential=<Credential>, SignedHeaders=content-length;content-type;host;user-agent;x-amz-content-sha256;x-amz-date;x-amz-target, Signature=<Signature>
User-Agent: <UserAgentString>
x-amz-content-sha256: <PayloadHash>
Content-Type: application/x-amz-json-1.0
Content-Length: <PayloadSizeBytes>     
Connection: Keep-Alive X-Amz-Target: DynamoDB_20120810.GetItem 

{
    "TableName": "Thread",
    "Key": {
        "ForumName": {
            "S": "Amazon DynamoDB"
        },
        "Subject": {
            "S": "How do I update multiple items?"
        }
    },
    "ProjectionExpression":"LastPostDateTime, Message, Tags",
    "ConsistentRead": true,
    "ReturnConsumedCapacity": "TOTAL"
}
        

Sample Response

HTTP/1.1 200 OK
x-amzn-RequestId: <RequestId> 
x-amz-crc32: <Checksum>
Content-Type: application/x-amz-json-1.0
Content-Length: <PayloadSizeBytes>
Date: <Date>
 {
    "ConsumedCapacity": {
        "CapacityUnits": 1,
        "TableName": "Thread"
    },
    "Item": {
        "Tags": {
            "SS": ["Update","Multiple Items","HelpMe"]
        },
        "LastPostDateTime": {
            "S": "201303190436"
        },
        "Message": {
            "S": "I want to update multiple items in a single API call. What's the best way to do that?"
        }
    }
}