如何：确定查询返回的实体数量（WCF 数据服务）

通过 WCF 数据服务，您可以确定由查询 URI 指定的实体集中的实体数量。 此计数可以与查询结果包含在一起，也可为一个整数值。 有关更多信息，请参见查询数据服务（WCF 数据服务）。

本主题中的示例使用 Northwind 示例数据服务和自动生成的客户端数据服务类。 此服务和这些客户端数据类是在完成 WCF 数据服务快速入门时创建的。

示例

此示例在调用 IncludeTotalCount 方法之后执行查询。 TotalCount 属性返回 Customers 实体集中实体的数量。

' 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(vbTab & "Customer 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);
}

此示例调用 Count 方法以仅返回一个整数值，该整数值是 Customers 实体集中的实体数量。

' 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);
}

请参阅

概念

查询数据服务（WCF 数据服务）