databinding in C# with paging and prefetch paths
Joined: 24-Nov-2008
I'm trying to understand how to successfully bind a LGP data source in C# (not within the .aspx file). I have my own GridView class and am overwriting the DataSource property with something like:
public override object DataSource
{
get
{
return base.DataSource;
}
set
{
// bind the given datasource
DataSource ds = (DataSource)value;
//ds.EnablePaging = true;
//ds.LivePersistence = false;
base.DataSource = ds;
try
{
base.DataBind();
}
catch (Exception ex)
{
throw new Exception(String.Format("Could not bind data to grid '{0}'.", base.ID), ex);
}
}
}
The given DS inherits from the LLBLGenProDataSource2 (could be based on a view, or on a table). It encapsulates information about the adapter, the namespace, etc. So I use it for example like this:
public class TeamSiListingDS : EntityDataSource, ISeasonalInstanceDS
{
public TeamSiListingDS(SeasonEntity season)
:
base()
{
// set the name of underlying entity
base.EntityName = "TeamSi";
// set the prefetch path
base.PrefetchPathToUse = getPrefetchPath();
}
public IPrefetchPath2 getPrefetchPath()
{
IPrefetchPath2 prefetch = new PrefetchPath2(EntityType.TeamSiEntity);
prefetch.Add(TeamSiEntity.PrefetchPathTeam_);
return prefetch;
}
}
A specific data grid could look like this:
public class TeamSiListingGV : GridView
{
public TeamSiListingGV()
:
base()
{
base.Columns.Add(new DataField("Team", "Team"));
// base.Columns.Add(new DataField("Team_.Moniker", "Moniker"));
base.DataSource = new TeamSiListingDS(null);
}
}
Everything works fine, as long as I don't want paging and do not try to access fields of other entities (prefetched by the given path, like the "Team" entity).
I have tried to look through various posts here in the forum, but I couldn't figure out, what the solution to the problems is.
-) If I enable paging, I run into a NullReferenceException during the binding event. -) Same if I try to access fields of related entities the way I would access them if not working with a DS. The message is: "A field or property with the name 'Team_.Moniker' was not found on the selected data source."
Various posts in the forum refer to the idea that the LivePersistence should be set to false and/or the EntityCollection set manually. But when I set the LivePersistence to false, the grid is not generated at all. I also don't quite understand what is meant by "EntityCollection set manually".
I hope there is somebody out there who is not totally confused by my explanation. 
If not, then I would appreciate some questions to be able to go into the right direction of details.
Also a link to an example/tutorial how something like this is done properly would be great. Or a comment that it should not be done this way at all. In this case I would appreciate some hints how.
Joined: 24-Nov-2008
Joined: 24-Nov-2008
Joined: 24-Nov-2008
Joined: 24-Nov-2008
Walaa wrote:
I think the prefetching is going fine. The problem is in databinding, as you can't dind a related entity's field as follows:
// base.Columns.Add(new DataField("Team_.Moniker", "Moniker"));
Better to use the Designer to create a field on related field, to have that Team.Moniker mapped to a field in the entity you are binding, so when you prefetch the Team related entity this field gets populated and hence usable in databinding.
1) Yes, the prefetching is going fine, but why is the binding not working? I thought I have seen some examples where this was done ... and if not, why is there no way to do it?
2) What would be the advantage of related fields against just creating views and having a data source based on the view?
The pain with this is still that I would have to create own structures (related fields, views, typed lists) for every single data source that I need, right? 
Joined: 24-Nov-2008
Joined: 24-Nov-2008
Walaa wrote:
I think you mean collect data on the server and show it on the client.
erm ... nope. We have a client software that is installed on laptops. The users collect statistics with these clients and submit data on a game by game basis to the server. For now, we don't have to edit this data, we just want to show it.
Walaa wrote:
For that I recomment using flat lists (TypedList, TypedView or DynamicList).
ok, but I still don't understand why I can't have "dynamic" prefetches/joins between tables and views. For each GridView that I want to create, I will have to create an own database view or list?
Joined: 24-Nov-2008
Joined: 24-Nov-2008
Walaa wrote:
well ... I can set a prefetch path in the data source, but I can't access the columns that were prefetched from other entities ... can I?
Yes you can. It was done in the ASP.NET 2.0 databinding example I refered to you.
My plan was to join the view with the needed table dynamically depending on which grid I want to display
That's a good reason to use a Dynamic List, where you can define fields from more than one table/view and the relations/Joins between them.
I spent quite a lot of time to try to understand this, and I must say that although I understand some parts of it now, I'm still far away from being happy about the possible solutions and having grasped the overall picture/solution.
First of all, I have done some more reading in the forum, and found this thread: http://www.llblgen.com/TinyForum/Messages.aspx?ThreadID=11114
What I don't understand is the fact, that from the described example it seems to be somehow possible to access properties of other entities in a datasource based on an entity collection. So what am I doing wrong that I can't access the "Moniker" property? The relation between teamSi and team is a m:1 relation (1 teamSi --> 1 team).
Second, creating the DynamicList (new DataTable()) is quite a pain because I have to manually "copy"/define all fields of the "base entity" (or "base view"), although I know that I'm interested in all.
I'm also not sure whether I'm looking at the piece of code relevant for my problem in the mentioned tutorials (http://www.llblgen.com/pages/files/Example_WebDatabinding_06062008.zip). The code below is from "AdapterWebApp" / Products.designer.cs:
protected void ProductsDS_PerformSelect(object sender, SD.LLBLGen.Pro.ORMSupportClasses.PerformSelectEventArgs2 e)
{
//Use a prefetchPath to Category, to display each Product's Category Name .
PrefetchPath2 prefetchPath = new PrefetchPath2((int)EntityType.ProductEntity);
prefetchPath.Add(ProductEntity.PrefetchPathCategory);
// build a list of fields to be execluded from the fetch.
ExcludeIncludeFieldsList execludedFields = new ExcludeIncludeFieldsList(true);
execludedFields.Add(ProductFields.UnitsInStock);
execludedFields.Add(ProductFields.UnitsOnOrder);
execludedFields.Add(ProductFields.ReorderLevel);
execludedFields.Add(ProductFields.SupplierId);
// use the DataAccessAdapter's FetchEntityCollection to fetch the contained collection
// pass the filter and sorter passed in the PerformSelectEventArgs2
// as well as the list of execluded fields.
DataAccessAdapter adapter = new DataAccessAdapter();
adapter.FetchEntityCollection(e.ContainedCollection, e.Filter, e.MaxNumberOfItemsToReturn, e.Sorter, prefetchPath, execludedFields, e.PageNumber, e.PageSize);
}
Do you mean that if I would add the prefetch path to the TeamEntity in a method overriding the PerformSelect method, I could then access the Moniker attribute? I don't understand how this would make a difference / be different from specifying the PrefetchPathToUser property ...
I also still don't understand why I can't find any examples of creating a LGP-DataSource for a GridView completely without defining it in the .aspx file ...
Joined: 24-Nov-2008
Joined: 08-Oct-2008
Joined: 24-Nov-2008
MTrinder wrote:
This section of the documentation descibes how to add a field to an entity to access the value of a field on a related entity.
Once this field has been generated into the entity code it can be bound like any other entity field - the only caveat to remember is that the related entity that the field refers to has to be exist in the graph with the parent entity.
Matt
thank you for the link. I'm starting to feel more and more like a dumbo ... I still don't get the overall picture:
-) What do you mean by "in the graph with the parent entity?" -) If I specify to add the field as described by you (shown in the tutorial), do I still have to use the prefetch path? I assume no, and that the bound attribute will be automatically fetched, right? -) How do the previously mentioned dynamic lists fit into this scenario?
Although I now know how to "fix the problem" in various ways, I'm still not really happy about the solution(s) because it still means that I have to address every possible display scenario used in a gridview "in advance". Meaning I can't just go ahead and join two tables (a table and a view etc.) "on runtime" = without creating a view, a list, or create associations in the LGP project in advance.
Joined: 08-Oct-2008
1) Let's take Customer-Order as it is the usual standard. Say you added the customer name field to the Order as described in the instructions. This would allow you to bind "Order.CustomerName" as you require. However, for this to return a value, the Customer entity needs to have been fetched as well as the Order entity - this is what "in the graph" means - a related entity loaded in memory.
this brings us to
2) Sorry, wrong 
You need to have fetched the Customer entity yourself by specifying the pre-fetch path at load time - Adapter performs NO lazy loading so it is your job to make sure that the data is there.
3) Give me 10 minutes to read back through and I'll get back to you...!
Matt
Joined: 08-Oct-2008
Sorry, I'm having problems following the thread of this thread What is it that you are trying to acheive using dynamic lists, that hasn't been addressed by the ability to access/bind a related field on an entity...?
Matt
Joined: 24-Nov-2008
MTrinder wrote:
Sorry, I'm having problems following the thread of this thread
thanks for the answers to (1) and (2). I'm starting to see the light at the end of the tunnel ... and it doesn't look like a train.
What I'm trying to achieve is a completely "dynamic" data source for a grid view. Basically basing a GridView on a db view without having to really create a view in the database.
So for example ... I start out with the OrderEntity (to stick to your example). If I want a GridView that shows more details about the CustomerEntity, I "join in" the customer. If I want to have more details about the product ordered, I "join in" the ProductEntity, or maybe also the "ProductCategory" entity.
I might need such views depending on how I look at the order, from a "customer's perspective", or from a "product's perspective" etc.
I know I can do this by creating a TypedList, a TypedView, or the solution mentioned by you, but do I really have to? I'd love to live/work without it.
Did I make the confusion perfect?
Joined: 08-Oct-2008