How to: Project Query Results (WCF Data Services)
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 OData V1-V3 has been superseded by OData V4, which is an industry standard published by OASIS and ratified by ISO.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.
Projection provides a mechanism to reduce the amount of data returned by a query by specifying that only certain properties of an entity are returned in the response. You can perform projections on the results of an WCF Data Services query either by using the $select query option or by using the select clause (Select in Visual Basic) in a LINQ query. 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
The following example shows a LINQ query that projects Customers entities into a new CustomerAddress type, which contains only address-specific properties plus the identity property. This CustomerAddress class is defined on the client and is attributed so that the client library can recognize it as an entity type.
// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);
// Define an anonymous LINQ query that projects the Customers type into
// a CustomerAddress type that contains only address properties.
var query = from c in context.Customers
where c.Country == "Germany"
select new CustomerAddress {
CustomerID = c.CustomerID,
Address = c.Address,
City = c.City,
Region = c.Region,
PostalCode = c.PostalCode,
Country = c.Country};
try
{
// Enumerate over the query result, which is executed implicitly.
foreach (var item in query)
{
// Modify the address and mark the object as updated.
item.Address += " #101";
context.UpdateObject(item);
// Write out the current values.
Console.WriteLine("Customer ID: {0} \r\nStreet: {1} "
+ "\r\nCity: {2} \r\nState: {3} \r\nZip Code: {4} \r\nCountry: {5}",
item.CustomerID, item.Address, item.City, item.Region,
item.PostalCode, item.Country);
}
// Save changes to the data service.
context.SaveChanges();
}
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 an anonymous LINQ query that projects the Customers type into
' a CustomerAddress type that contains only address properties.
Dim query = From c In context.Customers _
Where c.Country = "Germany" _
Select New CustomerAddress With { _
.CustomerID = c.CustomerID, _
.Address = c.Address, _
.City = c.City, _
.Region = c.Region, _
.PostalCode = c.PostalCode, _
.Country = c.Country}
Try
' Enumerate over the query result, which is executed implicitly.
For Each item In query
' Modify the address and mark the object as updated.
item.Address += " #101"
context.UpdateObject(item)
' Write out the current values.
Console.WriteLine("Customer ID: {0} " & vbCrLf & "Street: {1} " _
& vbCrLf & "City: {2} " & vbCrLf & "State: {3} " & vbCrLf & "Zip Code: {4}" _
& vbCrLf & "Country: {5}", _
item.CustomerID, item.Address, item.City, item.Region, _
item.PostalCode, item.Country)
Next
' Save changes to the data service.
context.SaveChanges()
Catch ex As DataServiceQueryException
Throw New ApplicationException( _
"An error occurred during query execution.", ex)
End Try
Example
The following example shows a LINQ query that projects returned Customers entities into a new CustomerAddressNonEntity type, which contains only address-specific properties and no identity property. This CustomerAddressNonEntity class is defined on the client and is not attributed as an entity type.
// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);
// Define an anonymous LINQ query that projects the Customers type into
// a CustomerAddress type that contains only address properties.
var query = from c in context.Customers
where c.Country == "Germany"
select new CustomerAddressNonEntity
{
CompanyName = c.CompanyName,
Address = c.Address,
City = c.City,
Region = c.Region,
PostalCode = c.PostalCode,
Country = c.Country
};
try
{
// Enumerate over the query result, which is executed implicitly.
foreach (var item in query)
{
item.Address += "Street";
Console.WriteLine("Company name: {0} \nStreet: {1} "
+ "\nCity: {2} \nState: {3} \nZip Code: {4} \nCountry: {5}",
item.CompanyName, item.Address, item.City, item.Region,
item.PostalCode, item.Country);
}
}
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 an anonymous LINQ query that projects the Customers type into
' a CustomerAddress type that contains only address properties.
Dim query = From c In context.Customers _
Where c.Country = "Germany" _
Select New CustomerAddressNonEntity With _
{.CompanyName = c.CompanyName, _
.Address = c.Address, _
.City = c.City, _
.Region = c.Region, _
.PostalCode = c.PostalCode, _
.Country = c.Country}
Try
' Enumerate over the query result, which is executed implicitly.
For Each item In query
item.Address += "Street"
Console.WriteLine("Company name: {0} " & vbNewLine & "Street: {1} " _
& "" & vbNewLine & "City: {2} " & vbNewLine & "State: {3} " & vbNewLine & _
"Zip Code: {4} " & vbNewLine & "Country: {5}", _
item.CompanyName, item.Address, item.City, item.Region, _
item.PostalCode, item.Country)
Next
Catch ex As DataServiceQueryException
Throw New ApplicationException( _
"An error occurred during query execution.", ex)
End Try
Example
The following example shows the definitions of the CustomerAddress and CustomerAddressNonEntity types that are used in the previous examples.
[DataServiceKey("CustomerID")]
public partial class CustomerAddress
{
private string _customerID;
private string _address;
private string _city;
private string _region;
private string _postalCode;
private string _country;
public string CustomerID
{
get
{
return this._customerID;
}
set
{
this._customerID = value;
}
}
public string Address
{
get
{
return this._address;
}
set
{
this._address = value;
}
}
public string City
{
get
{
return this._city;
}
set
{
this._city = value;
}
}
public string Region
{
get
{
return this._region;
}
set
{
this._region = value;
}
}
public string PostalCode
{
get
{
return this._postalCode;
}
set
{
this._postalCode = value;
}
}
public string Country
{
get
{
return this._country;
}
set
{
this._country = value;
}
}
}
public class CustomerAddressNonEntity
{
private string _companyName;
private string _address;
private string _city;
private string _region;
private string _postalCode;
private string _country;
public string CompanyName
{
get
{
return this._companyName;
}
set
{
this._companyName = value;
}
}
public string Address
{
get
{
return this._address;
}
set
{
this._address = value;
}
}
public string City
{
get
{
return this._city;
}
set
{
this._city = value;
}
}
public string Region
{
get
{
return this._region;
}
set
{
this._region = value;
}
}
public string PostalCode
{
get
{
return this._postalCode;
}
set
{
this._postalCode = value;
}
}
public string Country
{
get
{
return this._country;
}
set
{
this._country = value;
}
}
}
<DataServiceKey("CustomerID")> _
Partial Public Class CustomerAddress
Private _customerID As String
Private _address As String
Private _city As String
Private _region As String
Private _postalCode As String
Private _country As String
Public Property CustomerID() As String
Get
Return Me._customerID
End Get
Set(ByVal value As String)
Me._customerID = Value
End Set
End Property
Public Property Address() As String
Get
Return Me._address
End Get
Set(ByVal value As String)
Me._address = Value
End Set
End Property
Public Property City() As String
Get
Return Me._city
End Get
Set(ByVal value As String)
Me._city = Value
End Set
End Property
Public Property Region() As String
Get
Return Me._region
End Get
Set(ByVal value As String)
Me._region = Value
End Set
End Property
Public Property PostalCode() As String
Get
Return Me._postalCode
End Get
Set(ByVal value As String)
Me._postalCode = Value
End Set
End Property
Public Property Country() As String
Get
Return Me._country
End Get
Set(ByVal value As String)
Me._country = value
End Set
End Property
End Class
Public Class CustomerAddressNonEntity
Private _companyName As String
Private _address As String
Private _city As String
Private _region As String
Private _postalCode As String
Private _country As String
Public Property CompanyName() As String
Get
Return Me._companyName
End Get
Set(ByVal value As String)
Me._companyName = value
End Set
End Property
Public Property Address() As String
Get
Return Me._address
End Get
Set(ByVal value As String)
Me._address = Value
End Set
End Property
Public Property City() As String
Get
Return Me._city
End Get
Set(ByVal value As String)
Me._city = Value
End Set
End Property
Public Property Region() As String
Get
Return Me._region
End Get
Set(ByVal value As String)
Me._region = Value
End Set
End Property
Public Property PostalCode() As String
Get
Return Me._postalCode
End Get
Set(ByVal value As String)
Me._postalCode = Value
End Set
End Property
Public Property Country() As String
Get
Return Me._country
End Get
Set(ByVal value As String)
Me._country = value
End Set
End Property
End Class