AggregateOperand.Single(CriteriaOperator) Method

Creates a new AggregateOperand which returns the single object from the AggregateOperand.CollectionProperty that matches the specified AggregateOperand.Condition. The collection must be empty or contain exactly one object.

Namespace: DevExpress.Data.Filtering

Assembly: DevExpress.Data.v24.2.dll

Declaration

C#

public AggregateOperand Single(
    CriteriaOperator aggregatedExpression
)

VB.NET

Public Function Single(
    aggregatedExpression As CriteriaOperator
) As AggregateOperand

Parameters

Name	Type	Description
aggregatedExpression	CriteriaOperator	A CriteriaOperator object which specifies the aggregate expression.

Returns

Type	Description
AggregateOperand	An AggregateOperand object which calculates an aggregate expression.

Example

Example 1

Get a property’s value of a specific element from a child collection

Expression:

LINQ

CriteriaOperator.FromLambda<Order, string>(o => o.OrderItems.SingleOrDefault(oi => oi.ItemPrice == 40).OrderItemName);

Typed

new AggregateOperand(new OperandProperty(nameof(Order.OrderItems)), new OperandProperty(nameof(OrderItem.OrderItemName)), Aggregate.Single, new BinaryOperator(nameof(OrderItem.ItemPrice), 40));

String

CriteriaOperator.Parse("[OrderItems][ItemPrice=40].Single(OrderItemName)");

Test

Input:

Order	OrderItemName	ItemPrice
Order0
	OrderItem1	30
	OrderItem2	40

The result: OrderItem2

Example 2

Get a specific element from a child collection.

Expression:

LINQ

CriteriaOperator.FromLambda<Order, OrderItem>(o => o.OrderItems.SingleOrDefault(oi => oi.ItemPrice == 40));

Typed

new AggregateOperand(new OperandProperty(nameof(Order.OrderItems)), new OperandProperty("This"), Aggregate.Single, new BinaryOperator(nameof(OrderItem.ItemPrice), 40));

String

CriteriaOperator.Parse("[OrderItems][ItemPrice=40].Single()");

Test

Input:

Order	OrderItemId	OrderItemName	ItemPrice
Order0
	0	OrderItem1	30
	1	OrderItem2	40

The result: 1

Example 3

Get a specific element from a child collection and use it in another expression.

Expression:

LINQ

CriteriaOperator.FromLambda<OrderItem>(oi => oi.Order == FromLambdaFunctions.FreeJoin<Order>(o => o.OrderItems.Any(oii => oii.ItemPrice == 456)).SingleOrDefault());

Typed

var criterion = new AggregateOperand(new OperandProperty(nameof(Order.OrderItems)), null, Aggregate.Exists, new BinaryOperator(nameof(OrderItem.ItemPrice), 456));
var joinCriterion = new JoinOperand(nameof(Order), criterion, Aggregate.Single, new OperandProperty("This"));
var resultCriterion = new BinaryOperator(nameof(OrderItem.Order), joinCriterion);

String

CriteriaOperator.Parse("Order=[<Order>][[OrderItems][ItemPrice=456]].Single()");

Test

Input:

OrderId	Order	OrderItemName	ItemPrice
1	Order0
		OrderItem1	1
		OrderItem2	456
		OrderItem3	3
		OrderItem4	4
2	Order1
		OrderItem5	30
		OrderItem6	40

The result:

OrderItemName	ItemPrice
OrderItem1	1
OrderItem2	456
OrderItem3	3
OrderItem4	4