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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. You can use the ScanIndexForward parameter to get results in forward or reverse order, by sort key.
Queries that do not return results consume the minimum number of read capacity units for that type of read operation.
If the total number of items meeting the query criteria exceeds the result set size limit of 1 MB, the query stops and results are returned to the user with the LastEvaluatedKey element to continue the query in a subsequent operation. Unlike a Scan operation, a Query operation never returns both an empty result set and a LastEvaluatedKey value. LastEvaluatedKey is only provided if the results exceed 1 MB, or if you have used the Limit parameter.
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.
Namespace: Amazon.DynamoDBv2.Model
Assembly: AWSSDK.dll
Version: (assembly version)
public class QueryRequest : AmazonDynamoDBRequest IRequestEvents
The QueryRequest type exposes the following members
Name | Description | |
---|---|---|
QueryRequest() | Empty constructor used to set properties independently even when a simple constructor is available | |
QueryRequest(string) | Instantiates QueryRequest with the parameterized properties |
Name | Type | Description | |
---|---|---|---|
AttributesToGet | System.Collections.Generic.List<System.String> |
Gets and sets the property AttributesToGet. 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.
You cannot use both AttributesToGet and Select together in a Query
request, unless the value for Select is If you query 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 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. |
|
ConditionalOperator | Amazon.DynamoDBv2.ConditionalOperator |
Gets and sets the property ConditionalOperator. This is a legacy parameter, for backward compatibility. New applications should use FilterExpression instead. Do not combine legacy parameters and expression parameters in a single API call; otherwise, DynamoDB will return a ValidationException exception. A logical operator to apply to the conditions in a QueryFilter map:
If you omit ConditionalOperator, then The operation will succeed only if the entire map evaluates to true. This parameter does not support attributes of type List or Map. |
|
ConsistentRead | System.Boolean |
Gets and sets the property ConsistentRead.
Determines the read consistency model: If set to
Strongly consistent reads are not supported on global secondary indexes. If you query
a global secondary index with ConsistentRead set to |
|
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. |
|
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:
Use the # character in an expression to dereference an attribute name. For example, consider the following attribute name:
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:
You could then use this substitution in an expression, as in this example:
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. |
|
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:
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:
For more information on expression attribute values, see Specifying Conditions in the Amazon DynamoDB Developer Guide. |
|
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 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. FilterExpression replaces the legacy QueryFilter and ConditionalOperator parameters. |
|
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. |
|
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:
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:
Valid comparisons for the sort key condition are as follows:
Use the ExpressionAttributeValues parameter to replace tokens such as 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:
To work around this, define a placeholder (such a
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. KeyConditionExpression replaces the legacy KeyConditions parameter. |
|
KeyConditions | System.Collections.Generic.Dictionary<System.String, Amazon.DynamoDBv2.Model.Condition> |
Gets and sets the property KeyConditions. This is a legacy parameter, for backward compatibility. New applications should use KeyConditionExpression instead. Do not combine legacy parameters and expression parameters in a single API call; otherwise, DynamoDB will return a ValidationException exception.
The selection criteria for the query. For a query on a table, you can have conditions
only on the table primary key attributes. You must provide the partition key name
and value as an If you don't provide a sort key condition, all of the items that match the partition key will be retrieved. If a FilterExpression or QueryFilter is present, it will be applied after the items are retrieved.
For a query on an index, you can have conditions only on the index key attributes.
You must provide the index partition key name and value as an Each KeyConditions element consists of an attribute name to compare, along with the following:
For usage examples of AttributeValueList and ComparisonOperator, see Legacy Conditional Parameters in the Amazon DynamoDB Developer Guide. |
|
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. |
|
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. ProjectionExpression replaces the legacy AttributesToGet parameter. |
|
QueryFilter | System.Collections.Generic.Dictionary<System.String, Amazon.DynamoDBv2.Model.Condition> |
Gets and sets the property QueryFilter. This is a legacy parameter, for backward compatibility. New applications should use FilterExpression instead. Do not combine legacy parameters and expression parameters in a single API call; otherwise, DynamoDB will return a ValidationException exception. A condition that evaluates the query results after the items are read and returns only the desired values. This parameter does not support attributes of type List or Map. A QueryFilter is applied after the items have already been read; the process of filtering does not consume any additional read capacity units. If you provide more than one condition in the QueryFilter map, then by default all of the conditions must evaluate to true. In other words, the conditions are ANDed together. (You can use the ConditionalOperator parameter to OR the conditions instead. If you do this, then at least one of the conditions must evaluate to true, rather than all of them.) Note that QueryFilter does not allow key attributes. You cannot define a filter condition on a partition key or a sort key. Each QueryFilter element consists of an attribute name to compare, along with the following:
|
|
ReturnConsumedCapacity | Amazon.DynamoDBv2.ReturnConsumedCapacity | Gets and sets the property ReturnConsumedCapacity. | |
ScanIndexForward | System.Boolean |
Gets and sets the property ScanIndexForward.
Specifies the order for index traversal: If 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 |
|
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.
If neither Select nor AttributesToGet are specified, DynamoDB defaults
to
If you use the ProjectionExpression parameter, then the value for Select
can only be |
|
TableName | System.String |
Gets and sets the property TableName.
The name of the table containing the requested items. |
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".
// 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<AttributeValue> { new AttributeValue { S = "The Adventures" } } }; // Create the key conditions from hashKey and condition Dictionary<string, Condition> keyConditions = new Dictionary<string, Condition> { // Hash key condition. ComparisonOperator must be "EQ". { "Author", new Condition { ComparisonOperator = "EQ", AttributeValueList = new List<AttributeValue> { hashKey } } }, // Range key condition { "Title", condition } }; // Define marker variable Dictionary<string, AttributeValue> 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<Dictionary<string, AttributeValue>> items = result.Items; foreach (Dictionary<string, AttributeValue> 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>()), string.Join(", ", keyValuePair.Value.NS ?? new List<string>())); } } // 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<AttributeValue> { new AttributeValue { N = "1900" } } }; // Create the key conditions from hashKey and condition Dictionary<string, Condition> keyConditions = new Dictionary<string, Condition> { // Hash key condition. ComparisonOperator must be "EQ". { "Author", new Condition { ComparisonOperator = "EQ", AttributeValueList = new List<AttributeValue> { hashKey } } }, // Range key condition { "Year", // Reference the correct range key when using indexes condition } }; // Define marker variable Dictionary<string, AttributeValue> 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<Dictionary<string, AttributeValue>> items = result.Items; foreach (Dictionary<string, AttributeValue> 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>()), string.Join(", ", keyValuePair.Value.NS ?? new List<string>())); } } // Set marker variable startKey = result.LastEvaluatedKey; } while (startKey != null && startKey.Count > 0);
.NET Framework:
Supported in: 4.5, 4.0, 3.5
.NET for Windows Store apps:
Supported in: Windows 8.1, Windows 8
.NET for Windows Phone:
Supported in: Windows Phone 8.1, Windows Phone 8