Class QueryRequest

Namespace: Amazon.DynamoDBv2.Model

Assembly: AWSSDK.DynamoDBv2.dll

Container for the parameters to the Query operation. You must provide the name of the partition key attribute and a single value for that attribute.

Query

returns all items with that partition key value. Optionally, you can provide a sort key attribute and use a comparison operator to refine the search results.

Use the

KeyConditionExpression

parameter to provide a specific value for the partition key. The

Query

operation will return all of the items from the table or index with that partition key value. You can optionally narrow the scope of the

Query

operation by specifying a sort key value and a comparison operator in

KeyConditionExpression

. To further refine the

Query

results, you can optionally provide a

FilterExpression

. A

FilterExpression

determines which items within the results should be returned to you. All of the other results are discarded.

Query

operation always returns a result set. If no matching items are found, the result set will be empty. Queries that do not return results consume the minimum number of read capacity units for that type of read operation.

note

DynamoDB calculates the number of read capacity units consumed based on item size, not on the amount of data that is returned to an application. The number of capacity units consumed will be the same whether you request all of the attributes (the default behavior) or just some of them (using a projection expression). The number will also be the same whether or not you use a

FilterExpression

Query

results are always sorted by the sort key value. If the data type of the sort key is Number, the results are returned in numeric order; otherwise, the results are returned in order of UTF-8 bytes. By default, the sort order is ascending. To reverse the order, set the

ScanIndexForward

parameter to false.

A single

Query

operation will read 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 will need to paginate the result set. For more information, see Paginating the Results in the Amazon DynamoDB Developer Guide.

FilterExpression

is applied after a

Query

finishes, but before the results are returned. A

FilterExpression

cannot contain partition key or sort key attributes. You need to specify those attributes in the

KeyConditionExpression

note

Query

operation can return an empty result set and a

LastEvaluatedKey

if all the items read for the page of results are filtered out.

You can query a table, a local secondary index, or a global secondary index. For a query on a table or on a local secondary index, you can set the

ConsistentRead

parameter to

true

and obtain a strongly consistent result. Global secondary indexes support eventually consistent reads only, so do not specify

ConsistentRead

when querying a global secondary index.

public class QueryRequest : AmazonDynamoDBRequest

Inheritance: object

AmazonDynamoDBRequest

QueryRequest

Constructors

QueryRequest()

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

public QueryRequest()

QueryRequest(string)

Instantiates QueryRequest with the parameterized properties

public QueryRequest(string tableName)

Parameters

tableName string: The name of the table containing the requested items.

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.

Determines the read consistency model: If set to

true

, then the operation uses strongly consistent reads; otherwise, the operation uses eventually consistent reads.

Strongly consistent reads are not supported on global secondary indexes. If you query 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.

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 Specifying Conditions 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

Query

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

FilterExpression

criteria are not returned.

FilterExpression

does not allow key attributes. You cannot define a filter expression based on a partition key or a sort key.

note

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 an index to query. This index can be any local secondary index or global secondary index on the table. Note that if you use the

IndexName

parameter, you must also provide

TableName.

public string IndexName { get; set; }

Property Value

string

KeyConditionExpression

Gets and sets the property KeyConditionExpression.

The condition that specifies the key values for items to be retrieved by the

Query

action.

The condition must perform an equality test on a single partition key value.

The condition can optionally perform one of several comparison tests on a single sort key value. This allows

Query

to retrieve one item with a given partition key value and sort key value, or several items that have the same partition key value but different sort key values.

The partition key equality test is required, and must be specified in the following format:

partitionKeyName

:partitionkeyval

If you also want to provide a condition for the sort key, it must be combined using

AND

with the condition for the sort key. Following is an example, using the = comparison operator for the sort key:

partitionKeyName

:partitionkeyval

AND

sortKeyName

:sortkeyval

Valid comparisons for the sort key condition are as follows:

```
sortKeyName
```
```
=
```
```
:sortkeyval
```
- true if the sort key value is equal to
```
:sortkeyval
```
.
```
sortKeyName
```
```
<
```
```
:sortkeyval
```
- true if the sort key value is less than
```
:sortkeyval
```
.
```
sortKeyName
```
```
<=
```
```
:sortkeyval
```
- true if the sort key value is less than or equal to
```
:sortkeyval
```
.
```
sortKeyName
```
```
>
```
```
:sortkeyval
```
- true if the sort key value is greater than
```
:sortkeyval
```
.
```
sortKeyName
```
```
>=
```
```
:sortkeyval
```
- true if the sort key value is greater than or equal to
```
:sortkeyval
```
.
```
sortKeyName
```
```
BETWEEN
```
```
:sortkeyval1
```
```
AND
```
```
:sortkeyval2
```
- true if the sort key value is greater than or equal to
```
:sortkeyval1
```
, and less than or equal to
```
:sortkeyval2
```
.
```
begins_with (
```
```
sortKeyName
```
,
```
:sortkeyval
```
```
)
```
- true if the sort key value begins with a particular operand. (You cannot use this function with a sort key that is of type Number.) Note that the function name
```
begins_with
```
is case-sensitive.

Use the

ExpressionAttributeValues

parameter to replace tokens such as

:partitionval

and

:sortval

with actual values at runtime.

You can optionally use the

ExpressionAttributeNames

parameter to replace the names of the partition key and sort key with placeholder tokens. This option might be necessary if an attribute name conflicts with a DynamoDB reserved word. For example, the following

KeyConditionExpression

parameter causes an error because Size is a reserved word:

```
Size = :myval
```

To work around this, define a placeholder (such a

#S

) to represent the attribute name Size.

KeyConditionExpression

then is as follows:

```
#S = :myval
```

For a list of reserved words, see Reserved Words in the Amazon DynamoDB Developer Guide.

For more information on

ExpressionAttributeNames

and

ExpressionAttributeValues

, see Using Placeholders for Attribute Names and Values in the Amazon DynamoDB Developer Guide.

public string KeyConditionExpression { get; set; }

Property Value

string

KeyConditions

Gets and sets the property KeyConditions.

This is a legacy parameter. Use

KeyConditionExpression

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

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

Property Value

Dictionary<string, Condition>

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 Query and Scan 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 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.

public string ProjectionExpression { get; set; }

Property Value

string

QueryFilter

Gets and sets the property QueryFilter.

This is a legacy parameter. Use

FilterExpression

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

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

Property Value

Dictionary<string, Condition>

ReturnConsumedCapacity

Gets and sets the property ReturnConsumedCapacity.

public ReturnConsumedCapacity ReturnConsumedCapacity { get; set; }

Property Value

ReturnConsumedCapacity

ScanIndexForward

Gets and sets the property ScanIndexForward.

Specifies the order for index traversal: If

true

(default), the traversal is performed in ascending order; if

false

, the traversal is performed in descending order.

Items with the same partition key value are stored in sorted order by sort key. If the sort key data type is Number, the results are stored in numeric order. For type String, the results are stored in order of UTF-8 bytes. For type Binary, DynamoDB treats each byte of the binary data as unsigned.

ScanIndexForward

true

, DynamoDB returns the results in the order in which they are stored (by sort key value). This is the default behavior. If

ScanIndexForward

false

, DynamoDB reads the results in reverse order by sort key value, and then returns the results to the client.

public bool ScanIndexForward { get; set; }

Property Value

bool

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 will read 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

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.

public string TableName { get; set; }

Property Value

string

Table of Contents

Class QueryRequest

note

note

Constructors

QueryRequest()

QueryRequest(string)

Parameters

Properties

AttributesToGet

Property Value

ConditionalOperator

Property Value

ConsistentRead

Property Value

ExclusiveStartKey

Property Value

ExpressionAttributeNames

note

Property Value

ExpressionAttributeValues

Property Value

FilterExpression

note

Property Value

IndexName

Property Value

KeyConditionExpression

Property Value

KeyConditions

Property Value

Limit

Property Value

ProjectionExpression

Property Value

QueryFilter

Property Value

ReturnConsumedCapacity

Property Value

ScanIndexForward

Property Value

Select

note

Property Value

TableName

Property Value