With Great Power comes Great Response.write("Ability") : Debugging

Working with associations in ADO.NET Data Services , Part 2

PhaniRajuYN — Fri, 24 Oct 2008 00:01:46 GMT

In part 2 ,we will talk about how to use the client library to deal with :

1..N Associations

This is the case of entities associated with each other 1..N . An example from Northwind is the relation between Categories and Products Entities.

An instance of the Categories entity type should have associated Products entities, this is another way of saying “ A row in the Products table should have links to a row in the Categories table”.
In case of 1..N relations , the left( child ) ends of the association are expressed as Collection properties on the right ( parent ) end of the relation.
This is shown in the metadata of the service as :

<EntityType Name="Categories">
<!-- Primary Key-->
<Key>
  <PropertyRef Name="CategoryID" /> 
</Key>
 <!--Primitive Properties-->
  <Property Name="CategoryID" Type="Edm.Int32" Nullable="false" /> 
  <Property Name="CategoryName" Type="Edm.String" Nullable="false" /> 
  <Property Name="Description" Type="Edm.String" Nullable="true" /> 
  <Property Name="Picture" Type="Edm.Binary" Nullable="true" /> 
 <!-- Child Entity Set-->
  <NavigationProperty 
        Name="Products" 
        Relationship="northwind.FK_Products_Categories" 
        FromRole="Categories" 
        ToRole="Products" /> 
</EntityType>

This leads the client utility( DataSvcUtil.exe ) to generate a type Individual which has instances of types Customer and Contact as Properties.

The generated class on the client looks like this :

public class Categories {
  public global::System.Collections.ObjectModel.Collection<Products> Products {
            get {
                return this._Products;
            }
            set {
                if ((value != null))
                {
                    this._Products = value;
                }
            }
        }
}

Now that we have set the stage, lets look at how one would use the client library to interact with the related types.

Creating the link between the entities

You have new instances of Individual , Contact and Customer and you want to persist the new entities and their relation to the store.

DataServiceContext dsc = new DataServiceContext(new Uri("http://ServiceEndpoint"));
Categories freeProductsCategory = new Categories()
{
    CategoryName = "Free Products",
    Description = "These products are free",
};
Products freeHeadPhones = Products.CreateProducts(0, "Free Headphones", false);
Products freeZune = Products.CreateProducts(1, "Free Zune", false);

dsc.AddObject("Categories", freeProductsCategory);
dsc.AddObject("Products", freeHeadPhones);
dsc.AddObject("Products", freeZune);

Now what ?

Since the entities are created and added to the store can’t I just set the Customer and Contact Property to the Individual object and that will save the relation ?

freeProductsCategory.Products.Add(freeHeadPhones);
freeProductsCategory.Products.Add(freeZune);
dsc.SaveChanges();

Shouldn’t this be enough ?
Nope , that’s not enough to save the relation to the store.

Why ?

Remember that the client context only gives you POCO access to entities in the store and any new entities that you create.
The Client context does not track any relations unless you explicitly ask it to do so !

Neat , now how do I ask it to do that ?

You use the AddLink method defined on the context.

dsc.AddLink(freeProductsCategory, "Products", freeHeadPhones);
dsc.AddLink(freeProductsCategory, "Products", freeZune);

The signature and the intent of the SetLink method is lucid , it binds 2 entities into a relation , its kinda like a priest at a wedding,
This is what it looks like ..

AddLink ( Parentinstance ,”ChildPropertyName”,ChildInstance)

Deleting the parent entity

Deleting the parent entity means that the relations with the child entities are also removed.
Think of this as the argument of “How do I delete an entity that has 1..1 links with other entities?”

What happens if I delete the parent entity without deleting the links ?

It depends on your store . If your database is configured to do a cascade delete on deletion of the parent entity ,you might get away with deleting the entity without removing the links

The right way to delete the entity is to remove all the links it has with the child entities and then delete the entity itself.
The code would look like this..

DataServiceContext dsc = new DataServiceContext(new Uri("http://ServiceEndpoint"));
//Load an existing parent
Categories freeProductsCategory = dsc
                                  .CreateQuery<Categories>("Categories")
                                  .Where(cat => cat.CategoryName == "Free Products")
                                  .First();
//Load all the related child Entities
dsc.LoadProperty(freeProductsCategory, "Products");

//Delete the links with each of the child entities
foreach (Products freeProduct in freeProductsCategory.Products) {
    dsc.DeleteLink(freeProductsCategory, "Products", freeProduct);
}
//Delete the parent entity
dsc.DeleteObject(freeProductsCategory);
dsc.SaveChanges();

Wait !! what’s with the LoadProperty there ?
Well, if you need to delete the relation , the way to identify the relation or the link is to have both the right and the left end of the relations to be materialized. without the expand , the Contact and the Customer property are null , and we don’t know which relation to delete.In case of 1..1 relations it might be easy to predict based on the relation name ,
but wouldn’t be easy in case of 1..n relations.

Deleting the child entity

//Load an existing parent
Categories freeProductsCategory = dsc
                                   .CreateQuery<Categories>("Categories")
                                   .Where(cat => cat.CategoryName == "Free Products")
                                   .First();
//Load all the related child Entities
dsc.LoadProperty(freeProductsCategory, "Products");

//Delete the links with each of the child entities
foreach (Products freeProduct in freeProductsCategory.Products) {
    dsc.DeleteLink(freeProductsCategory, "Products", freeProduct);
    //Delete the child entity
    dsc.DeleteObject(freeProduct);
}
dsc.SaveChanges();

Special Consideration for Navigation properties that are named differently than the Entity Type

This is a special case because of a bug in the client library at the time of writing this post.
If you have a navigation property which is named differently than the EntityType and try to delete the link between the source
and the navigation property , we produce an invalid URI for the DELETE of the link.

ex:

Entity Type : Customers , EntitySet Name : Customers
Navigation Properties :
EntityType : Orders , Navigation Property Name : CashOrders
EntityType : Orders , Navigation Property Name : CreditCardOrders

Upon calling ,
dataContext.DeleteLink(customerInstance,”CashOrders”,orderInstance);

We generate a DELETE to the URI
/Customers(Key)/$links/Orders(Key)
This is wrong , the DELETE should go to :
/Customers(Key)/$links/CashOrders(Key)

We will address this issue in a future release .In the meantime , use the workaround below ,

public partial class YourDataContextClass {

    public void DeleteLinkManual(object source, string associationName, object target) {
            System.Uri UriOfParent;
            System.Uri UriOfChild;
            this.TryGetUri(source, out UriOfParent);
            this.TryGetUri(target, out UriOfChild);

            //Get the Segment of the URI with the Key 
            string strChildAssociationURI = UriOfChild.Segments.Last();
            strChildAssociationURI = strChildAssociationURI.Substring(strChildAssociationURI.IndexOf('('));

            //ServiceEndPoint/ParentEntitySet/$links/NavigationPropertyName(ChildEntitySetKey)
            string requestUriForLinkDelete = System.String.Format("{0}/{1}/$links/{2}{3}",
                                             this.BaseUri.OriginalString,
                                             UriOfParent.Segments.Last(),
                                             associationName,
                                             strChildAssociationURI);

            System.Net.WebRequest request = System.Net.WebRequest.Create(requestUriForLinkDelete);
            request.Method = "DELETE";
            System.Net.HttpWebResponse response = request.GetResponse() as System.Net.HttpWebResponse;
            if (response.StatusCode != System.Net.HttpStatusCode.NoContent)
            {
                throw (new System.Data.Services.Client.DataServiceClientException("Delete Failed"));
            }
            //Detach this link as the link no longer exists and keep the context consistent
            this.DetachLink(source, associationName, target);
      }
}

and then , in your code ,

YourDataContext dataContext = new YourDataContext(<Uri>);
dataContext.DeleteLinkManual(customerInstance,”CashOrders”,orderInstance);

This will produce the right URI :

ServiceEndPoint/Customers(Key)/$links/CashOrders(Key)

Note that this doesnt work in Silverlight , I will create a separate sample for Silverlight later .

If you have any questions , leave a comment . If you have any issues with code and need help , please post your query on the astoria forums as I can’t promise that I will be able to reply to emails sent to me directly .The whole team is very active on the forums and the more eyes on a problem the better.

Astoria & IIS , HTTP 400 Bad Request on Posting Large Payloads to an astoria service

PhaniRajuYN — Mon, 06 Oct 2008 05:35:00 GMT

We’ve seen this in the labs and also reported by our customers on the forums, If you try to post a large amount of data to
an astoria data service , you might receive a response code Http 400 Bad Request even though the response data is valid.

An ADO.NET Data Service sits on top of Windows Communication Foundation , although most of the required plumbing is hidden away from you , you can still see the effects in scenarios such as this .

Why do I get a generic 400 Bad Request in this case ?

When the request size ( including headers ) exceeds 64 K ( 65536 bytes ) , WCF chokes on the request as this request size is greater than the limit on the maximum size of the request the service can recieve and sends out a HTTP 400 Bad Request as the request is invalid.

How do I fix this ?

a)The maximum size of the request which a WCF service can process is controlled by the MaxReceivedMessageSize property on the WCF binding.
The default value is 65536 ,exceeding which you get the 400 response code.

In the web.config of the web site hosting the service , add the following node in the <System.ServiceModel> section.

<system.serviceModel> 
<services> 
  <!-- The name of the service --> 
  <service name="NorthwindService"> 
    <!-- you can leave the address blank or specify your end point URI --> 
    <endpoint address ="YourServiceEndpoint" 
              binding="webHttpBinding" bindingConfiguration="higherMessageSize" 
     contract ="System.Data.Services.IRequestHandler"> 
    </endpoint> 
  </service> 
</services> 
<bindings> 
  <webHttpBinding> 
    <!-- configure the maxReceivedMessageSize  value to suit the max size of 
         the request ( in bytes ) you want the service to recieve--> 
    <binding name="higherMessageSize" maxReceivedMessageSize ="MaxMessageSize"/> 
  </webHttpBinding> 
</bindings> 
<serviceHostingEnvironment aspNetCompatibilityEnabled="true"/> 
</system.serviceModel>

b) If hosted on IIS , the ASP.Net Request Size restriction can also cause a large request to be rejected,
You will need to set the HttpRuntimeSection.MaxRequestLength Property.

<system.web> 
  <httpRuntime MaxRequestLength="ValueInKiloBytes" />
</system.web>

How do I Identify if the reason I am seeing a 400 Bad Request is because of the request size ?

Identify if WCF is throwing an exception under the covers which is not being surfaced to you at the HTTP level.
You can configure WCF tracing on the server-side to log the necessary information from the WCF layer.
Once you have tracing setup and you reproduced the failure , check if the log contains one or both of these exception messages.

System.ServiceModel.ProtocolException
"The maximum message size quota for incoming messages (65536) has been exceeded. 
To increase the quota, use the MaxReceivedMessageSize property on the appropriate binding element."

System.Web.HttpException
"Maximum request length exceeded."

If you see that the log does contain this message , then you can be sure that the failure is because of the message size
and apply this fix accordingly.

Debugging Ado.net Data Services

PhaniRajuYN — Wed, 18 Jun 2008 21:52:00 GMT

When developing your service , you might run into some issues and you want to debug your service.
Imagine that you are inserting data into the store using astoria and you start getting DataServiceExceptions in your client code.
The normal error message would be ..

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<error xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">
  <code></code>
  <message xml:lang="en-US">An error occurred while processing this request.</message>
</error>

While debugging the service , you would need more information that just this generic error message .
To switch to the dev error mode, you can use the following config settings.

1) Set UseVerboseErrors to true in the ServiceConfiguration

public class YoruService : DataService<YourProvider> {
   public static void InitializeService(IDataServiceConfiguration config) {       
       config.UseVerboseErrors = true;
        . . . . . .        
    }
......

Once this mode is setup , your error messages look like this ..

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<error xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">
  <code></code>
  <message xml:lang="en-US">An error occurred while processing this request.</message>
  <innererror xmlns="xmlns">
    <message>An error occurred while updating the entries. See the InnerException for details.</message>
    <type>System.Data.UpdateException</type>
    <stacktrace>   at System.Data.Mapping.Update.Internal.UpdateTranslator.Update(IEntityStateManager stateManager, IEntityAdapter adapter)&#xD;
   at System.Data.Objects.ObjectContext.SaveChanges(Boolean acceptChangesDuringSave)&#xD;
   at System.Data.Services.Providers.ObjectContextServiceProvider.SaveChanges()&#xD;
   at System.Data.Services.DataService`1.HandleNonBatchRequest(RequestDescription description)&#xD;
   at System.Data.Services.DataService`1.HandleRequest()</stacktrace>
    <internalexception>
      <message>Violation of PRIMARY KEY constraint 'PK_Region'. Cannot insert duplicate key in object 'dbo.Region'.&#xD;
The statement has been terminated.</message>
      <type>System.Data.SqlClient.SqlException</type>
      <stacktrace>   at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)&#xD;
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)&#xD;
   at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)&#xD;
   at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)&#xD;
   at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async)&#xD;
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result)&#xD;
   at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe)&#xD;
   at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()&#xD;
   at System.Data.Mapping.Update.Internal.DynamicUpdateCommand.Execute(UpdateTranslator translator, EntityConnection connection, Dictionary`2 identifierValues, List`1 generatedValues)&#xD;
   at System.Data.Mapping.Update.Internal.UpdateTranslator.Update(IEntityStateManager stateManager, IEntityAdapter adapter)</stacktrace>
    </internalexception>
  </innererror>
</error>

This works well when you have a working service all prepped up and ready to go .
But , what do you do when your service won't even start ?

If the service fails to initialize due to some error , you get the generic WCF Error message,
which is seldom useful .

The error message would look like this ..

The reason you see this and not the Pretty formatted error message from astoria is that the astoria framework
never initialized the service and failed in the WCF pipeline.
To see the error at this layer , you will need to

2) Configure your Servicebehavior with the IncludeExceptionDetailInFaults attribute.

Via Code :

[System.ServiceModel.ServiceBehavior(IncludeExceptionDetailInFaults = true)]   
public class YourService : DataService<YourProvider>

Via Config :

<system.serviceModel> <services> <service name="ServiceNamespace.ServiceClassName" behaviorConfiguration ="DebugEnabled"> </service> </services> <behaviors> <serviceBehaviors > <behavior name="DebugEnabled"> <serviceDebug includeExceptionDetailInFaults="True"/> </behavior> </serviceBehaviors> </behaviors> <serviceHostingEnvironment aspNetCompatibilityEnabled="true"/> </system.serviceModel>

After setting this config , this is what the error  looks like ..

 
Happy Debugging !