Compartilhar via

How to: Determine the Number of Entities Returned by a Query (WCF Data Services)

  • Artigo

Important

WCF Data Services has been deprecated and will no longer be available for download from the Microsoft Download Center. WCF Data Services supported earlier versions of the Microsoft OData (V1-V3) protocol only and has not been under active development. OData V1-V3 has been superseded by OData V4, which is an industry standard published by OASIS and ratified by ISO. OData V4 is supported through the OData V4 compliant core libraries available at Microsoft.OData.Core. Support documentation is available at OData.Net, and the OData V4 service libraries are available at Microsoft.AspNetCore.OData.

RESTier is the successor to WCF Data Services. RESTier helps you bootstrap a standardized, queryable, HTTP-based REST interface in minutes. Like WCF Data Services before it, Restier provides simple and straightforward ways to shape queries and intercept submissions before and after they hit the database. And like Web API + OData, you still have the flexibility to add your own custom queries and actions with techniques you're already familiar with.

With WCF Data Services, you can determine the number of entities that are in the entity set specified by a query URI. This count can be included either along with the query result or as an integer value. For more information, see Querying the Data Service.

The example in this topic uses the Northwind sample data service and autogenerated client data service classes. This service and the client data classes are created when you complete the WCF Data Services quickstart.

Example

This example executes a query after calling the IncludeTotalCount method. The TotalCount property returns the number of entities in the Customers entity set.

// 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);
}

' 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

Example

This example calls the Count method to return only an integer value that is the number of entities in the Customers entity set.

// 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);
}

' 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

See also