[dba-VB] ADO.NET Entity Model

Hi Gustav,

Thank you for your information on ADO.NET Entity Model. I must say I personally haven't yet tried to use it...

--
Shamil

-----Original Message-----
From: "Gustav Brock" <Gustav at cactus.dk>
To: <dba-vb at databaseadvisors.com>
Date: Sat, 07 Mar 2009 15:41:25 +0100
Subject: Re: [dba-VB] ADO.NET Entity Model

> Hi all
> 
> Also, the fill method is now vastly reduced.
> 
>     protected void OwnerDropDownList_Init(object sender, EventArgs e)
>     {
>         LocationDropDownList.DataValueField = "Id";
>         LocationDropDownList.DataTextField = "Location1";
>     }
> 
>     private void FillLocationDropDownList()
>     {
>         LocationDropDownList.DataSource = _erhvervslejeContext.LocationByOwnerQuery;
>         LocationDropDownList.DataBind();
>     }
> 
> /gustav
> 
> 
> >>> Gustav at cactus.dk 07-03-2009 15:27 >>>
> Hi all
> 
> I finally found out how to return Location rather than anonymous types:
> 
>   public ObjectQuery<Location> LocationByOwnerQuery
>         {
>             get
>             {
>                 ObjectQuery <Location> locationByOwner;
>                 if (_locationFilterOwner != null)
>                 {
>                     locationByOwner =
>                         Location 
>                         .Where("it.Owner.Id = @ownerId",
>                         new ObjectParameter ("ownerId", _locationFilterOwner.Id));
>                 }
>                 else
>                 {
>                     locationByOwner =
>                         Location;
>                 }
>                 return locationByOwner;
>             }
>         }
> 
> Now, how could I use the object Owner as parameter and not Owner.Id?
> This is not accepted:
> 
>  .Where("it.Owner = @owner", new ObjectParameter ("owner", _locationFilterOwner));
> 
> as only scalar values are accepted as parameter values.
> 
> /gustav
> 
> 
> >>> Gustav at cactus.dk 06-03-2009 17:53 >>>
> Hi all, sorry being serious on a Friday, but this is really bugging me ...
> 
> I wish to retrieve a list of locations for the DataSource of a DropDownList.
> The entity model does have a collection of Location which I can retrieve and cast to a list like this:
> 
> > In .. .aspx.cs file:
> 
>     private void FillLocationDropDownList()
>     {
>         var locationQuery = (from l in _erhvervslejeContext.Location
>                              select new
>                             {
>                                 Id = l.Id,
>                                 Location1 = l.Location1
>                             }).ToList();
>         LocationDropDownList.DataSource = locationQuery; 
>         LocationDropDownList.DataBind();
>     }
> 
> However, I have added an ObjectQuery to the entity model, which filters Location, LocationByOwnerQuery (shown below):
> 
>     private void FillLocationDropDownList()
>     {
>         var locationQuery = (from l in _erhvervslejeContext.Location
>                              select new
>                             {
>                                 Id = l.Id,
>                                 Location1 = l.Location1
>                             }).ToList();
>         LocationDropDownList.DataSource = locationQuery; 
>         LocationDropDownList.DataBind();
>     }
> 
> 
> Now, if I try to retrieve this as a list as shown, an error is raised at the var line:
> 
> " .. Cannot create a constant value of the type 'erhvervslejeModel.erhvervslejeEntities'.
> Only primitive types ('like Int32, String og Guid') are supported in this context. .."
> 
> I know I could just do a foreach loop to add the items into the listbox but that is just a bit too primitive.
> 
> Any suggestions?
> 
> /gustav
> 
> > in     public partial class erhvervslejeEntities : global::System.Data.Objects.ObjectContext
> 
>         public ObjectQuery<Location> LocationByOwnerQuery
>         {
>             get
>             {
>                 IQueryable query;
>                 if (_locationFilterOwner != null)
>                 {
>                     query =
>                         from
>                             Location location in this.Location
>                         where
>                             location.Owner.Equals(_locationFilterOwner)
>                         select 
>                             location;
>                 }
>                 else
>                 {
>                     query =
>                         from
>                             Location location in this.Location
>                         select
>                             location;
>                 }
>                 return (query as ObjectQuery<Location>);
>             }
>         }
> 
> ***
> 
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