AWS SDK Version 3 for .NET
API Reference

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Container for the parameters to the Query operation. The Query operation finds items based on primary key values. You can query any table or secondary index that has a composite primary key (a partition key and a sort key).

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.

A 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.

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.

A 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.

Inheritance Hierarchy

System.Object
  Amazon.Runtime.AmazonWebServiceRequest
    Amazon.DynamoDBv2.AmazonDynamoDBRequest
      Amazon.DynamoDBv2.Model.QueryRequest

Namespace: Amazon.DynamoDBv2.Model
Assembly: AWSSDK.DynamoDBv2.dll
Version: 3.x.y.z

Syntax

C#
public class QueryRequest : AmazonDynamoDBRequest
         IAmazonWebServiceRequest

The QueryRequest type exposes the following members

Constructors

NameDescription
Public Method QueryRequest()

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

Public Method QueryRequest(string)

Instantiates QueryRequest with the parameterized properties

Properties

NameTypeDescription
Public Property AttributesToGet System.Collections.Generic.List<System.String>

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 Property ConditionalOperator Amazon.DynamoDBv2.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 Property ConsistentRead System.Boolean

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 Property ExclusiveStartKey System.Collections.Generic.Dictionary<System.String, Amazon.DynamoDBv2.Model.AttributeValue>

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 Property ExpressionAttributeNames System.Collections.Generic.Dictionary<System.String, System.String>

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

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.

Public Property ExpressionAttributeValues System.Collections.Generic.Dictionary<System.String, Amazon.DynamoDBv2.Model.AttributeValue>

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 Property FilterExpression System.String

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.

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

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 Property IndexName System.String

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 Property KeyConditionExpression System.String

Gets and sets the property KeyConditionExpression.

The condition that specifies the key value(s) 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 also perform one of several comparison tests on a single sort key value. Query can use KeyConditionExpression 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=:partitionkeyvalANDsortKeyName=: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.

  • sortKeyNameBETWEEN:sortkeyval1AND: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 Property KeyConditions System.Collections.Generic.Dictionary<System.String, Amazon.DynamoDBv2.Model.Condition>

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 Property Limit System.Int32

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 data set 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 Property ProjectionExpression System.String

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 Property QueryFilter System.Collections.Generic.Dictionary<System.String, Amazon.DynamoDBv2.Model.Condition>

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 Property ReturnConsumedCapacity Amazon.DynamoDBv2.ReturnConsumedCapacity

Gets and sets the property ReturnConsumedCapacity.

Public Property ScanIndexForward System.Boolean

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 ASCII character code values. For type Binary, DynamoDB treats each byte of the binary data as unsigned.

If ScanIndexForward is true, DynamoDB returns the results in the order in which they are stored (by sort key value). This is the default behavior. If ScanIndexForward is false, DynamoDB reads the results in reverse order by sort key value, and then returns the results to the client.

Public Property Select Amazon.DynamoDBv2.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 will fetch 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 AttributesToGet. This return value is equivalent to specifying AttributesToGet 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 will fetch 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 AttributesToGet 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 AttributesToGet together in a single request, unless the value for Select is SPECIFIC_ATTRIBUTES. (This usage is equivalent to specifying AttributesToGet without any value for Select.)

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 Property TableName System.String

Gets and sets the property TableName.

The name of the table containing the requested items.

Examples

The following example shows how to query items in a table.
Note: the Query operation retrieves items that have the same hash-key. This means that the Query operation is only supported on tables with both a hash- and a range-key.
Note: the RangeKeyCondition for Query is limited to indexable comparisons. These are EQ, LE, LT, GE, GT, BETWEEN, and BEGINS_WITH.
We will now retrieve all items where the hash-key is "Mark Twain" and the range-key begins with the string "The Adventures".

Query sample


// Create a client
AmazonDynamoDBClient client = new AmazonDynamoDBClient();

// Define item hash-key to be string value "Mark Twain"
AttributeValue hashKey = new AttributeValue { S = "Mark Twain" };

// Define query condition to search for range-keys that begin with the string "The Adventures"
Condition condition = new Condition
{
    ComparisonOperator = "BEGINS_WITH",
    AttributeValueList = new List
    {
        new AttributeValue { S = "The Adventures" }
    }
};

// Create the key conditions from hashKey and condition
Dictionary keyConditions = new Dictionary
{
    // Hash key condition. ComparisonOperator must be "EQ".
    { 
        "Author",
        new Condition
        {
            ComparisonOperator = "EQ",
            AttributeValueList = new List { hashKey }
        }
    },
    // Range key condition
    {
        "Title",
        condition
    }
};

// Define marker variable
Dictionary startKey = null;

do
{
    // Create Query request
    QueryRequest request = new QueryRequest
    {
        TableName = "SampleTable",
        ExclusiveStartKey = startKey,
        KeyConditions = keyConditions
    };

    // Issue request
    var result = client.Query(request);

    // View all returned items
    List> items = result.Items;
    foreach (Dictionary item in items)
    {
        Console.WriteLine("Item:");
        foreach (var keyValuePair in item)
        {
            Console.WriteLine("{0} : S={1}, N={2}, SS=[{3}], NS=[{4}]",
                keyValuePair.Key,
                keyValuePair.Value.S,
                keyValuePair.Value.N,
                string.Join(", ", keyValuePair.Value.SS ?? new List()),
                string.Join(", ", keyValuePair.Value.NS ?? new List()));
        }
    }

    // Set marker variable
    startKey = result.LastEvaluatedKey;
} while (startKey != null && startKey.Count > 0);

                

The following example shows how to query items in a local secondary index.
Like a standard Query, we must pass in a hash-key value. But since we are querying against a specific index, we must remember to refer to the correct index attribute.
In the below example that means that we reference the attribute "Years", and since the attribute is numerical we must pass in a numerical AttributeValue.


// Create a client
AmazonDynamoDBClient client = new AmazonDynamoDBClient();

// Define item hash-key to be string value "Mark Twain"
AttributeValue hashKey = new AttributeValue { S = "Mark Twain" };

// Define query condition to search for range-keys ("Year", in "YearsIndex") that are less than 1900
Condition condition = new Condition
{
    ComparisonOperator = "LT",
    AttributeValueList = new List
    {
        new AttributeValue { N = "1900" }
    }
};

// Create the key conditions from hashKey and condition
Dictionary keyConditions = new Dictionary
{
    // Hash key condition. ComparisonOperator must be "EQ".
    { 
        "Author",
        new Condition
        {
            ComparisonOperator = "EQ",
            AttributeValueList = new List { hashKey }
        }
    },
    // Range key condition
    {
        "Year", // Reference the correct range key when using indexes
        condition
    }
};

// Define marker variable
Dictionary startKey = null;

do
{
    // Create Query request
    QueryRequest request = new QueryRequest
    {
        TableName = "SampleTable",
        ExclusiveStartKey = startKey,
        KeyConditions = keyConditions,
        IndexName = "YearsIndex" // Specify the index to query against
    };

    // Issue request
    var result = client.Query(request);

    // View all returned items
    List> items = result.Items;
    foreach (Dictionary item in items)
    {
        Console.WriteLine("Item:");
        foreach (var keyValuePair in item)
        {
            Console.WriteLine("{0} : S={1}, N={2}, SS=[{3}], NS=[{4}]",
                keyValuePair.Key,
                keyValuePair.Value.S,
                keyValuePair.Value.N,
                string.Join(", ", keyValuePair.Value.SS ?? new List()),
                string.Join(", ", keyValuePair.Value.NS ?? new List()));
        }
    }

    // Set marker variable
    startKey = result.LastEvaluatedKey;
} while (startKey != null && startKey.Count > 0);

                

Version Information

.NET Standard:
Supported in: 1.3

.NET Framework:
Supported in: 4.5, 4.0, 3.5

Portable Class Library:
Supported in: Windows Store Apps
Supported in: Windows Phone 8.1
Supported in: Xamarin Android
Supported in: Xamarin iOS (Unified)
Supported in: Xamarin.Forms

Unity:
Supported Versions: 4.6 and above
Supported Platforms: Android, iOS, Standalone