Crm plugin update fails - plugins

Question

I have created two new fields named "Price" for quote and quote product and I want to update the second every time I update the first.
Here is my code:
protected void ExecutePostAccountUpdateContacts(LocalPluginContext localContext)
{
if (localContext == null)
{
throw new ArgumentNullException("localContext");
}
string oldPrice = "";
string newPrice = "";
IPluginExecutionContext context = localContext.PluginExecutionContext;
IOrganizationService service = localContext.OrganizationService;
var ServiceContext = new OrganizationServiceContext(service);
ITracingService tracingService = localContext.TracingService;
if (context.InputParameters.Contains("Target") &&
context.InputParameters["Target"] is Entity)
{
Entity entity = (Entity)context.InputParameters["Target"];
Entity preImageEntity = (context.PreEntityImages != null && context.PreEntityImages.Contains(this.preImageAlias)) ? context.PreEntityImages[this.preImageAlias] : null;
// get the post entity image
Entity postImageEntity = (context.PostEntityImages != null && context.PostEntityImages.Contains(this.postImageAlias)) ? context.PostEntityImages[this.postImageAlias] : null;
if (preImageEntity.Attributes.Contains("Price"))
{
oldPrice = (string)preImageEntity.Attributes["Price"];
}
if (postImageEntity.Attributes.Contains("Price"))
{
newPrice = (string)postImageEntity.Attributes["Price"];
}
if (newPrice != oldPrice)
{
try
{
//Create query to get the related contacts
var res = from c in ServiceContext.CreateQuery("Products")
where c["parentQuoteid"].Equals(entity.Id)
select c;
foreach (var c in res)
{
Entity e = (Entity)c;
e["Price"] = newPrice;
ServiceContext.UpdateObject(e);
}
ServiceContext.SaveChanges();
}
catch (FaultException ex)
{
throw new InvalidPluginExecutionException("An error occurred in the plug-in.", ex);
}
}
}
}

Answer 1

Although you haven't asked a question, your query isn't quite right. So I am assuming your plugin fails when querying for product with a parentquoteid.
Not all linq operators are implemented, also , pass the entity logical name to the create query as a parameter, so instead of Products, just product. There is no out of the box field called parentquoteid, are you missing your custom attribute prefix?
var res = from c in ServiceContext.CreateQuery("product")
where c.GetAttributeValue<Guid>("new_parentquoteid") == entity.Id
select c;