HOW TO：判斷查詢傳回的實體數目 (WCF Data Services)

您可以使用 WCF Data Services ，判斷由查詢 URI 所指定之實體集中的實體數目。 這個計劃可能包含在查詢結果中或包含為整數值。 如需詳細資訊，請參閱查詢資料服務 (WCF Data Services)。

本主題的範例使用 Northwind 範例資料服務和自動產生的用戶端資料服務類別。 此服務和用戶端資料類別會在您完成 WCF Data Services 快速入門時建立。

範例

這個範例會在呼叫 IncludeTotalCount 方法之後執行查詢。 TotalCount 屬性會傳回 Customers 實體集中的實體數目。

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

' Define a new query for Customers that includes the total count.
Dim query As DataServiceQuery(Of Customer) = _
context.Customers.IncludeTotalCount()

Try
    ' Execute the query for all customers and get the response object.
    Dim response As QueryOperationResponse(Of Customer) = _
        CType(query.Execute(), QueryOperationResponse(Of Customer))

    ' Retrieve the total count from the response.
    Console.WriteLine("There are a total of {0} customers.", response.TotalCount)

    ' Enumerate the customers in the response.
    For Each customer As Customer In response
        Console.WriteLine("\tCustomer Name: {0}", customer.CompanyName)
    Next
Catch ex As DataServiceQueryException
    Throw New ApplicationException( _
            "An error occurred during query execution.", ex)
End Try

// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);
         
// Define a new query for Customers that includes the total count.
DataServiceQuery<Customer> query = context.Customers.IncludeTotalCount();

try
{    
    // Execute the query for all customers and get the response object.
    QueryOperationResponse<Customer> response = 
        query.Execute() as QueryOperationResponse<Customer>;

    // Retrieve the total count from the response.
    Console.WriteLine("There are a total of {0} customers.", response.TotalCount);

    // Enumerate the customers in the response.
    foreach (Customer customer in response)
    {
        Console.WriteLine("\tCustomer Name: {0}", customer.CompanyName);
    }
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred during query execution.", ex);
}

這個範例會呼叫 Count 方法，以便僅傳回代表 Customers 實體集中之實體數目的整數值。

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

' Define a new query for Customers.
Dim query As DataServiceQuery(Of Customer) = context.Customers

Try
    ' Execute the query to just return the value of all customers in the set.
    Dim totalCount = query.Count()

    ' Retrieve the total count from the response.
    Console.WriteLine("There are {0} customers in total.", totalCount)
Catch ex As DataServiceQueryException
    Throw New ApplicationException( _
            "An error occurred during query execution.", ex)
End Try

// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);
         
// Define a new query for Customers.
DataServiceQuery<Customer> query = context.Customers;

try
{    
    // Execute the query to just return the value of all customers in the set.
    int totalCount = query.Count();
    
    // Retrieve the total count from the response.
    Console.WriteLine("There are {0} customers in total.", totalCount);
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred during query execution.", ex);
}

另請參閱

概念

查詢資料服務 (WCF Data Services)