How to make queries to a WCF service with EF model / data first - wcf

Question

I have a client project and a MVC3 EF model first project that exposes a WCF service to the client. I am new to EF and some things are not so clear.
Lets assume the Northwind service with Product entity, if i want to make a simple query like return the products with a specific price, where do i write the code for the query ?
On the server side there is only EDM and the service itself and it is pretty straighforward, hardly any code there.
On the client i have Product model class and NorthwindContext and also a ProdcutsPageViewModel class (it's a MVVM project)
So my question is, How and where do i make queries to the DB ? do i make it from the client side by attaching LINQ code to the URI ? do i make it from the server side by adding new methods to the service ? I would appreciate if you could explain it to a newbie,
Thanks !
Here is some of the code :
On the server, the NorthwindODataService service class:
[ServiceBehavior(IncludeExceptionDetailInFaults = true)]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
public class NorthwindODataService : DataService<NorthwindEntities>
{
private readonly IUserPrivilegesRepository userPrivilegesRepository;
private readonly IClaimsIdentity identity;
public NorthwindODataService()
: this(HttpContext.Current.User.Identity as IClaimsIdentity, new InfrastructureEntities())
{
}
public NorthwindODataService(IClaimsIdentity identity, IUserPrivilegesRepository userPrivilegesRepository)
{
this.identity = identity;
this.userPrivilegesRepository = userPrivilegesRepository;
}
protected string UserId
{
get
{
var nameIdentifierClaim = this.identity.Claims.SingleOrDefault(c => c.ClaimType == ClaimTypes.NameIdentifier);
if (nameIdentifierClaim == null)
{
throw new DataServiceException(401, "Unauthorized", "The request requires authentication.", "en-US", null);
}
return nameIdentifierClaim.Value;
}
}
/// <summary>
/// Initializes service-wide policies. This method is called only once.
/// </summary>
/// <param name="config"></param>
public static void InitializeService(DataServiceConfiguration config)
{
config.SetEntitySetAccessRule("Products", EntitySetRights.All);
config.SetEntitySetAccessRule("Categories", EntitySetRights.AllRead);
config.SetEntitySetAccessRule("Suppliers", EntitySetRights.AllRead);
config.SetEntitySetPageSize("Products", 20);
config.SetEntitySetPageSize("Categories", 20);
config.SetEntitySetPageSize("Suppliers", 20);
config.DataServiceBehavior.MaxProtocolVersion = DataServiceProtocolVersion.V2;
config.UseVerboseErrors = true;
}
/// <summary>
/// Define a query interceptor for the Products entity set.
/// </summary>
/// <returns></returns>
[QueryInterceptor("Products")]
public Expression<Func<Product, bool>> OnQueryProducts()
{
this.ValidateAuthorization("Products", PrivilegeConstants.SqlReadPrivilege);
// The user has Read permission.
return p => true;
}
/// <summary>
/// Define a query interceptor for the Categories entity set.
/// </summary>
/// <returns></returns>
[QueryInterceptor("Categories")]
public Expression<Func<Category, bool>> OnQueryCategories()
{
this.ValidateAuthorization("Categories", PrivilegeConstants.SqlReadPrivilege);
// The user has Read permission.
return p => true;
}
/// <summary>
/// Define a query interceptor for the Suppliers entity set.
/// </summary>
/// <returns></returns>
[QueryInterceptor("Suppliers")]
public Expression<Func<Supplier, bool>> OnQuerySuppliers()
{
this.ValidateAuthorization("Suppliers", PrivilegeConstants.SqlReadPrivilege);
// The user has Read permission.
return p => true;
}
/// <summary>
/// Define a change interceptor for the Products entity set.
/// </summary>
/// <param name="product"></param>
/// <param name="operations"></param>
[ChangeInterceptor("Products")]
public void OnChangeProducts(Product product, UpdateOperations operations)
{
if (operations == UpdateOperations.Change)
{
this.ValidateAuthorization("Products", PrivilegeConstants.SqlUpdatePrivilege);
var entry = default(ObjectStateEntry);
if (this.CurrentDataSource.ObjectStateManager.TryGetObjectStateEntry(product, out entry))
{
// Reject changes to a discontinued Product.
// Because the update is already made to the entity by the time the
// change interceptor in invoked, check the original value of the Discontinued
// property in the state entry and reject the change if 'true'.
if ((bool)entry.OriginalValues["Discontinued"])
{
throw new DataServiceException(400, "Bad Request", "A discontinued product cannot be modified.", "en-US", null);
}
}
else
{
throw new DataServiceException(404, "Not Found", "The requested product could not be found in the data source.", "en-US", null);
}
}
else if (operations == UpdateOperations.Add)
{
this.ValidateAuthorization("Products", PrivilegeConstants.SqlCreatePrivilege);
}
else if (operations == UpdateOperations.Delete)
{
this.ValidateAuthorization("Products", PrivilegeConstants.SqlDeletePrivilege);
var entry = default(ObjectStateEntry);
if (this.CurrentDataSource.ObjectStateManager.TryGetObjectStateEntry(product, out entry))
{
// Only a discontinued Product can be deleted.
if (!(bool)entry.OriginalValues["Discontinued"])
{
throw new DataServiceException(400, "Bad Request", "Products that are not discontinued cannot be deleted.", "en-US", null);
}
}
else
{
throw new DataServiceException(404, "Not Found", "The requested product could not be found in the data source.", "en-US", null);
}
}
}
private static string BuildMessage(string entitySetName, string privilege)
{
var message = string.Empty;
switch (privilege)
{
case PrivilegeConstants.SqlCreatePrivilege:
message = string.Format(CultureInfo.InvariantCulture, "You are not authorized to create new rows in the {0} entity set.", entitySetName);
break;
case PrivilegeConstants.SqlReadPrivilege:
message = string.Format(CultureInfo.InvariantCulture, "You are not authorized to query the {0} entity set.", entitySetName);
break;
case PrivilegeConstants.SqlUpdatePrivilege:
message = string.Format(CultureInfo.InvariantCulture, "You are not authorized to update rows in the {0} entity set.", entitySetName);
break;
case PrivilegeConstants.SqlDeletePrivilege:
message = string.Format(CultureInfo.InvariantCulture, "You are not authorized to delete rows in the {0} entity set.", entitySetName);
break;
default:
message = string.Format(CultureInfo.InvariantCulture, "You are not authorized to access the {0} entity set.", entitySetName);
break;
}
return message;
}
private void ValidateAuthorization(string entitySetName, string privilege)
{
if (!this.userPrivilegesRepository.HasUserPrivilege(this.UserId, privilege))
{
// The user does not have Read permission.
throw new DataServiceException(401, "Unauthorized", BuildMessage(entitySetName, privilege), "en-US", null);
}
}
}
}
on the client, the Product model class:
[EntitySetAttribute("Products")]
[DataServiceKeyAttribute("ProductID")]
public class Product : INotifyPropertyChanged
{
private int id;
private string productName;
private int? supplierID;
private int? categoryID;
private string quantityPerUnit;
private decimal? unitPrice;
private short? unitsInStock;
private short? unitsOnOrder;
private short? reorderLevel;
private bool discontinued;
public event PropertyChangedEventHandler PropertyChanged;
public int ProductID
{
get
{
return this.id;
}
set
{
this.id = value;
this.OnPropertyChanged("ProductID");
}
}
public string ProductName
{
get
{
return this.productName;
}
set
{
this.productName = value;
this.OnPropertyChanged("ProductName");
}
}
public int? SupplierID
{
get
{
return this.supplierID;
}
set
{
this.supplierID = value;
this.OnPropertyChanged("SupplierID");
}
}
public int? CategoryID
{
get
{
return this.categoryID;
}
set
{
this.categoryID = value;
this.OnPropertyChanged("CategoryID");
}
}
public string QuantityPerUnit
{
get
{
return this.quantityPerUnit;
}
set
{
this.quantityPerUnit = value;
this.OnPropertyChanged("QuantityPerUnit");
}
}
public decimal? UnitPrice
{
get
{
return this.unitPrice;
}
set
{
this.unitPrice = value;
this.OnPropertyChanged("UnitPrice");
}
}
public short? UnitsInStock
{
get
{
return this.unitsInStock;
}
set
{
this.unitsInStock = value;
this.OnPropertyChanged("UnitsInStock");
}
}
public short? UnitsOnOrder
{
get
{
return this.unitsOnOrder;
}
set
{
this.unitsOnOrder = value;
this.OnPropertyChanged("UnitsOnOrder");
}
}
public short? ReorderLevel
{
get
{
return this.reorderLevel;
}
set
{
this.reorderLevel = value;
this.OnPropertyChanged("ReorderLevel");
}
}
public bool Discontinued
{
get
{
return this.discontinued;
}
set
{
this.discontinued = value;
this.OnPropertyChanged("Discontinued");
}
}
public static Product CreateProduct(int productID, string productName, bool discontinued)
{
return new Product
{
ProductID = productID,
ProductName = productName,
Discontinued = discontinued,
};
}
protected virtual void OnPropertyChanged(string changedProperty)
{
var propertyChanged = this.PropertyChanged;
if (propertyChanged != null)
{
propertyChanged(this, new PropertyChangedEventArgs(changedProperty));
}
}
}
}
And the NorthwindContext class:
public class NorthwindContext : DataServiceContext
{
public NorthwindContext(Uri serviceRoot)
: base(serviceRoot)
{
this.MergeOption = MergeOption.OverwriteChanges;
this.SaveChangesDefaultOptions = SaveChangesOptions.ContinueOnError;
}
public void AddToCategories(Category category)
{
this.AddObject("Categories", category);
}
public void AddToProducts(Product product)
{
this.AddObject("Products", product);
}
public void AddToSuppliers(Supplier supplier)
{
this.AddObject("Suppliers", supplier);
}
public void AttachToCategories(Category category)
{
this.AttachTo("Categories", category);
}
public void AttachToProducts(Product product)
{
this.AttachTo("Products", product);
}
public void AttachToSuppliers(Supplier supplier)
{
this.AttachTo("Suppliers", supplier);
}
}
}
and here is the ProductsPageViewModel class :
public class ProductsPageViewModel : ListViewModel<Product>
{
public ProductsPageViewModel()
: this(Deployment.Current.Dispatcher, App.CloudClientFactory.ResolveNorthwindContext())
{
}
public ProductsPageViewModel(Dispatcher dispatcher, NorthwindContext northwindContext)
: base(dispatcher, northwindContext)
{
}
protected override string EntitySetName
{
get
{
return "Products";
}
}
}
}

Answer 1

When you are working with EF, it doesn't suppose any direct queries to the database. Spent some time reading what is Domain Driven Design. There is described strategy Persistent Ignorance, which means, that when you are designing your system you should not consider data storage at all. Work only with the model. Data Mapper pattern describes the place where all the things related with the database should be done. Here is good article, which I think can help you.
Another advice, do not forget that MVC supports restful style of Web Development. Leveraging these capabilities should be helpful in your design.

Answer 2

paramosh,
So are you able to explain it to a newbie or not? I just went to that website, and read through that page, but it wasn't really much help for trying to lean the EF network (it's mainly reinforcing how I did things prior to EF).