Class ScanRequest

Namespace

Amazon.DynamoDBv2.Model

Assembly

AWSSDK.DynamoDBv2.dll

Container for the parameters to the Scan operation. The

Scan

operation returns one or more items and item attributes by accessing every item in a table or a secondary index. To have DynamoDB return fewer items, you can provide a

FilterExpression

operation.

If the total number of scanned items exceeds the maximum dataset size limit of 1 MB, the scan stops and results are returned to the user as a

LastEvaluatedKey

value to continue the scan in a subsequent operation. The results also include the number of items exceeding the limit. A scan can result in no table data meeting the filter criteria.

A single

Scan

operation reads up to the maximum number of items set (if using the

Limit

parameter) or a maximum of 1 MB of data and then apply any filtering to the results using

FilterExpression

. If

LastEvaluatedKey

is present in the response, you need to paginate the result set. For more information, see Paginating the Results in the Amazon DynamoDB Developer Guide.

Scan

operations proceed sequentially; however, for faster performance on a large table or secondary index, applications can request a parallel

Scan

operation by providing the

Segment

and

TotalSegments

parameters. For more information, see Parallel Scan in the Amazon DynamoDB Developer Guide.

Scan

uses eventually consistent reads when accessing the data in a table; therefore, the result set might not include the changes to data in the table immediately before the operation began. If you need a consistent copy of the data, as of the time that the

Scan

begins, you can set the

ConsistentRead

parameter to

true

.

public class ScanRequest : AmazonDynamoDBRequest

Inheritance

object

AmazonDynamoDBRequest

ScanRequest

Constructors

ScanRequest()

Empty constructor used to set properties independently even when a simple constructor is available

public ScanRequest()

ScanRequest(string)

Instantiates ScanRequest with the parameterized properties

public ScanRequest(string tableName)

Parameters

tableName string

The name of the table containing the requested items; or, if you provide

IndexName

, the name of the table to which that index belongs.

Properties

AttributesToGet

Gets and sets the property AttributesToGet.

This is a legacy parameter. Use

ProjectionExpression

instead. For more information, see AttributesToGet in the Amazon DynamoDB Developer Guide.

public List<string> AttributesToGet { get; set; }

Property Value

List<string>

ConditionalOperator

Gets and sets the property ConditionalOperator.

This is a legacy parameter. Use

FilterExpression

instead. For more information, see ConditionalOperator in the Amazon DynamoDB Developer Guide.

public ConditionalOperator ConditionalOperator { get; set; }

Property Value

ConditionalOperator

ConsistentRead

Gets and sets the property ConsistentRead.

A Boolean value that determines the read consistency model during the scan:

• If

  ConsistentRead

  is

  false

  , then the data returned from

  Scan

  might not contain the results from other recently completed write operations (

  PutItem

  ,

  UpdateItem

  , or

  DeleteItem

  ).

• If

  ConsistentRead

  is

  true

  , then all of the write operations that completed before the

  Scan

  began are guaranteed to be contained in the

  Scan

  response.

The default setting for

ConsistentRead

is

false

.

The

ConsistentRead

parameter is not supported on global secondary indexes. If you scan a global secondary index with

ConsistentRead

set to true, you will receive a

ValidationException

.

public bool ConsistentRead { get; set; }

Property Value

bool

ExclusiveStartKey

Gets and sets the property ExclusiveStartKey.

The primary key of the first item that this operation will evaluate. Use the value that was returned for

LastEvaluatedKey

in the previous operation.

The data type for

ExclusiveStartKey

must be String, Number or Binary. No set data types are allowed.

In a parallel scan, a

Scan

request that includes

ExclusiveStartKey

must specify the same segment whose previous

Scan

returned the corresponding value of

LastEvaluatedKey

.

public Dictionary<string, AttributeValue> ExclusiveStartKey { get; set; }

Property Value

Dictionary<string, AttributeValue>

ExpressionAttributeNames

Gets and sets the property 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 Specifying Item Attributes in the Amazon DynamoDB Developer Guide.

public Dictionary<string, string> ExpressionAttributeNames { get; set; }

Property Value

Dictionary<string, string>

ExpressionAttributeValues

Gets and sets the property 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.

public Dictionary<string, AttributeValue> ExpressionAttributeValues { get; set; }

Property Value

Dictionary<string, AttributeValue>

FilterExpression

Gets and sets the property FilterExpression.

A string that contains conditions that DynamoDB applies after the

Scan

operation, but before the data is returned to you. Items that do not satisfy the

FilterExpression

criteria are not returned.

note

A

FilterExpression

is applied after the items have already been read; the process of filtering does not consume any additional read capacity units.

For more information, see Filter Expressions in the Amazon DynamoDB Developer Guide.

public string FilterExpression { get; set; }

Property Value

string

IndexName

Gets and sets the property IndexName.

The name of a secondary index to scan. This index can be any local secondary index or global secondary index. Note that if you use the

IndexName

parameter, you must also provide

TableName

.

public string IndexName { get; set; }

Property Value

string

Limit

Gets and sets the property Limit.

The maximum number of items to evaluate (not necessarily the number of matching items). If DynamoDB processes the number of items up to the limit while processing the results, it stops the operation and returns the matching values up to that point, and a key in

LastEvaluatedKey

to apply in a subsequent operation, so that you can pick up where you left off. Also, if the processed dataset size exceeds 1 MB before DynamoDB reaches this limit, it stops the operation and returns the matching values up to the limit, and a key in

LastEvaluatedKey

to apply in a subsequent operation to continue the operation. For more information, see Working with Queries in the Amazon DynamoDB Developer Guide.

public int Limit { get; set; }

Property Value

int

ProjectionExpression

Gets and sets the property ProjectionExpression.

A string that identifies one or more attributes to retrieve from the specified table or index. 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 Specifying Item Attributes in the Amazon DynamoDB Developer Guide.

public string ProjectionExpression { get; set; }

Property Value

string

ReturnConsumedCapacity

Gets and sets the property ReturnConsumedCapacity.

public ReturnConsumedCapacity ReturnConsumedCapacity { get; set; }

Property Value

ReturnConsumedCapacity

ScanFilter

Gets and sets the property ScanFilter.

This is a legacy parameter. Use

FilterExpression

instead. For more information, see ScanFilter in the Amazon DynamoDB Developer Guide.

public Dictionary<string, Condition> ScanFilter { get; set; }

Property Value

Dictionary<string, Condition>

Segment

Gets and sets the property Segment.

For a parallel

Scan

request,

Segment

identifies an individual segment to be scanned by an application worker.

Segment IDs are zero-based, so the first segment is always 0. For example, if you want to use four application threads to scan a table or an index, then the first thread specifies a

Segment

value of 0, the second thread specifies 1, and so on.

The value of

LastEvaluatedKey

returned from a parallel

Scan

request must be used as

ExclusiveStartKey

with the same segment ID in a subsequent

Scan

operation.

The value for

Segment

must be greater than or equal to 0, and less than the value provided for

TotalSegments

.

If you provide

Segment

, you must also provide

TotalSegments

.

public int Segment { get; set; }

Property Value

int

Select

Gets and sets the property Select.

The attributes to be returned in the result. You can retrieve all item attributes, specific item attributes, the count of matching items, or in the case of an index, some or all of the attributes projected into the index.

• ALL_ATTRIBUTES

  - Returns all of the item attributes from the specified table or index. If you query a local secondary index, then for each matching item in the index, DynamoDB fetches the entire item from the parent table. If the index is configured to project all item attributes, then all of the data can be obtained from the local secondary index, and no fetching is required.

• ALL_PROJECTED_ATTRIBUTES

  - Allowed only when querying an index. Retrieves all attributes that have been projected into the index. If the index is configured to project all attributes, this return value is equivalent to specifying

  ALL_ATTRIBUTES

  .

• COUNT

  - Returns the number of matching items, rather than the matching items themselves.

• SPECIFIC_ATTRIBUTES

  - Returns only the attributes listed in

  ProjectionExpression

  . This return value is equivalent to specifying

  ProjectionExpression

  without specifying any value for

  Select

  .

  If you query or scan a local secondary index and request only attributes that are projected into that index, the operation reads only the index and not the table. If any of the requested attributes are not projected into the local secondary index, DynamoDB fetches each of these attributes from the parent table. This extra fetching incurs additional throughput cost and latency.

  If you query or scan a global secondary index, you can only request attributes that are projected into the index. Global secondary index queries cannot fetch attributes from the parent table.

If neither

Select

nor

ProjectionExpression

are specified, DynamoDB defaults to

ALL_ATTRIBUTES

when accessing a table, and

ALL_PROJECTED_ATTRIBUTES

when accessing an index. You cannot use both

Select

and

ProjectionExpression

together in a single request, unless the value for

Select

is

SPECIFIC_ATTRIBUTES

. (This usage is equivalent to specifying

ProjectionExpression

without any value for

Select

.)

note

If you use the

ProjectionExpression

parameter, then the value for

Select

can only be

SPECIFIC_ATTRIBUTES

. Any other value for

Select

will return an error.

public Select Select { get; set; }

Property Value

Select

TableName

Gets and sets the property TableName.

The name of the table containing the requested items; or, if you provide

IndexName

, the name of the table to which that index belongs.

public string TableName { get; set; }

Property Value

string

TotalSegments

Gets and sets the property TotalSegments.

For a parallel

Scan

request,

TotalSegments

represents the total number of segments into which the

Scan

operation will be divided. The value of

TotalSegments

corresponds to the number of application workers that will perform the parallel scan. For example, if you want to use four application threads to scan a table or an index, specify a

TotalSegments

value of 4.

The value for

TotalSegments

must be greater than or equal to 1, and less than or equal to 1000000. If you specify a

TotalSegments

value of 1, the

Scan

operation will be sequential rather than parallel.

If you specify

TotalSegments

, you must also specify

Segment

.

public int TotalSegments { get; set; }

Property Value

int