Cómo: Determinar el número de entidades devueltas por una consulta (WCF Data Services)
Con Servicios de datos de Microsoft WCF, puede determinar el número de entidades que existen en el conjunto de entidades especificado por un URI de consulta. Este número se puede incluir junto con el resultado de la búsqueda o como valor entero. Para obtener más información, vea Consultar el servicio de datos (WCF Data Services).
En el ejemplo de este tema se usa el servicio de datos de ejemplo Northwind y las clases del servicio de datos de cliente generadas automáticamente. Se crean este servicio y las clases de datos del cliente al completar el tutorial rápido del servicio de datos de WCF.
Ejemplo
En este ejemplo se ejecuta una consulta después de llamar al método IncludeTotalCount. La propiedad TotalCount devuelve el número de entidades del conjunto de entidades Customers.
' 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);
}
En este ejemplo se llama al método Count para devolver únicamente un valor entero que es el número de entidades del conjunto de entidades Customers.
' 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);
}