Apologies if this has been asked before as I am learning EF 4.1 and LINQ, I needed an expert opinion.
I have a viewmodel called HomeIndexData. My code looks something like the following:
string _categoryIDs = "100,101,102,103,104";
List < int > CategoryIDs = _categoryIDs.Split(',').Select(t => int.Parse(t));
Then I got the following view model:
public class HomeIndexData
{
public IEnumerable<Genre> Genres { get; set; }
public IEnumerable<Category> Categories { get; set; }
public IEnumerable<SubCategory> SubCategories { get; set; }
public IEnumerable<Country> Countries { get; set; }
}
At the moment, in my Controller I have the following code -
HomeIndexData viewModel = new HomeIndexData
{
Genres = db.Genres
.Include(i => i.Categories.Where(i => CategoryIDs.Contains(i.CategoryId)))
.Include("Categories.SubCategories")
.OrderBy(g => g.DisplaySequence),
Countries = db.countries
};
But I am getting error :
Cannot convert lambda expression to type 'string' because it is not a delegate type
for the following line :
.Include(i => i.Categories.Where(i => CategoryIDs.Contains(i.CategoryId)))
Could you please put me to the right direction how can I write the lamda expression.
Any help on this will be much appreciated.
Thanks in advance.
EF doesn't support complex expressions in the Include extension at this point, only simple property getters. If you feel this is an important enhancement scenario for EF, consider voting for it at http://data.uservoice.com/forums/72025-entity-framework-feature-suggestions/suggestions/1015345-allow-filtering-for-include-extension-method.
For now, your best option is to project your filter in the Select clause, but that gets tricky with a generic repository.
Related
I was looking at the demo:
Telerik's Demo
and this
Telerik's Example
I still cannot figure out how, using this technique, to pass a parameter
to the Read method, so instead of reading ALL games or products, it reads ONLY a
subset of games or products, by category ID lest say. If I change the Read method in
the server-side code to take a parameter, it never gets hit anymore,
and I cannot figure out how to pass a parameter from the transport
client-side definition definition... Any help would be highly
appreciated!
I posted the question to the Telerik's forums and got this which should work!
Telerik's Answer
In case anyone else comes along in the future and the link in the other answer is gone, or for those who don't want to download a project file and sift through it themselves, here's more detail from the answer given on the Telerik forums:
They use Kendo.DynamicLinq to "bind the request parameters."
They created a custom class that mirrors the structure of the existing DataSourceRequest class typically used in AJAX grid actions.
using System.Collections.Generic;
using Kendo.DynamicLinq;
namespace SignalRLocalHub.Models
{
public class MyDataSourceRequest
{
public int Take { get; set; }
public int Skip { get; set; }
public int Page { get; set; }
public int PageSize { get; set; }
public Filter Filter { get; set; }
public IEnumerable<Sort> Sort { get; set; }
public IEnumerable<Aggregator> Aggregates { get; set; }
}
}
In the ProductHub (SignalR hub) class, this is the Read method:
public DataSourceResult Read(MyDataSourceRequest request)
{
return productService.Read()
.ToDataSourceResult(
request.Take,
request.Skip,
request.Sort,
request.Filter,
request.Aggregates);
}
The productService.Read method it calls, for reference, looks like this:
//int take, int skip, IEnumerable<Sort> sort, Filter filter, IEnumerable<Aggregator> aggregates
public IQueryable<ProductViewModel> Read()
{
return entities.Products
.OrderBy(p => p.ProductID)
.Select(product => new ProductViewModel
{
ProductID = product.ProductID,
ProductName = product.ProductName,
UnitPrice = product.UnitPrice.HasValue ? product.UnitPrice.Value : default(decimal),
UnitsInStock = product.UnitsInStock.HasValue ? product.UnitsInStock.Value : default(short),
Discontinued = product.Discontinued
});
}
And finally, here is the grid's DataSource configuration:
.DataSource(d => d
.SignalR()
.AutoSync(true)
.Transport(tr => tr
.Promise("hubStart")
.Hub("hub")
.Client(c => c.Read("read").Create("create").Update("update").Destroy("destroy"))
.Server(s => s.Read("read").Create("create").Update("update").Destroy("destroy"))
)
.ServerFiltering(true)
.Filter(f => f.Add(m => m.UnitPrice).IsEqualTo(10))
.ServerPaging(true)
.PageSize(10)
.Schema(s => s
.Data("Data")
.Total("Total")
.Aggregates("Aggregates")
.Model(m =>
{
m.Id(e => e.ProductID);
m.Field(e => e.ProductID).Editable(false);
})
)
)
This allows sorting, paging, and filtering by any field that is part of the grid view model. So as long as your "category ID" is a property of the grid view model and the grid is configured to be able to filter by that field, this method should work.
I have a web api 2 application, and in my controller , I have this code :
[Queryable]
public IQueryable<Title> GetTitles()
{
return db.Titles;
}
and here is the Title entity :
public partial class Title
{
public Title()
{
this.People = new HashSet<Person>();
}
public short Id { get; set; }
public string NameT { get; set; }
public virtual ICollection<Person> People { get; set; }
}
When people query the Titles, they must get only "NameT" property. but now they get all of the properties. and yes, I know about $select, but I want another way. means even they use $select, they should not able to get "Id" property for example. if I have to bring more information, please tell me. thanks.
There are two ways to solve your problem when you use ODataController. However, they won't affect ApiController non-query part.
In that condition, you can try what Zoe suggested.
1.Ignore those properties while building your model with model builder.
builder.EntityType<Title>().Ignore(title => title.Id);
2.Add ignore member attributes on those properties.
[IgnoreDataMember]
public short Id { get; set; }
More than these, we provide support for limiting the set of allowed queries in Web API 2.2 for OData v4.0.
http://blogs.msdn.com/b/webdev/archive/2014/03/13/getting-started-with-asp-net-web-api-2-2-for-odata-v4-0.aspx
We can use attributes like Unsortable, NonFilterable, NotExpandable or NotNavigable on the properties of the types in our model, or we can configure this explicitly in the model builder.
Maybe you can have filter in your action GetTitles(), like:
[Queryable]
public IQueryable<Title> GetTitles()
{
return db.Titles.Select(t=>t.Name);
}
Use the ODataModelBuilder class as opposed to the ODataConventionModelBuilder class.
var modelBuilder = new ODataModelBuilder();
var titles = modelBuilder.EntitySet<Title>("titles");
var title = titles.EntityType;
title.HasKey(x => x.Id);
title.Ignore(x => x.Id);
title.Property(x => x.TName);
titles.HasIdLink(x => { return x.GenerateSelfLink(true); }, true);
config.Routes.MapODataRoute("odata", "odata", modelBuilder.GetEdmModel());
I store User objects in RavenDB. Each User has a User.Id property.
I also have a Relationship class that links two User.Ids together to create a Mentor/Mentee relationship, like this:
public class User
{
public string Id { get; set; }
public string UserName { get; set; }
... more properties
}
public class Relationship
{
public string Id { get; set; }
public string MentorId { get; set; }
public string MenteeId { get; set; }
public RelationshipStatus Status { get; set; }
}
Now I want to retrieve a list of Mentees for a given Mentor. I have done this in the following way:
public static List<User> GetMentees(IDocumentSession db, string mentorId)
{
var mentees = new List<User>();
db.Query<Relationship>()
.Where(r => r.MentorId == mentorId)
.Select(r => r.MenteeId)
.ForEach(id => mentees.Add(db.Load<User>(id)));
return mentees;
}
This seems to work just fine but the coding-angel on my shoulder is wrinkling her nose at the smells emanating from the nested use of the IDocumentSession (db) and the need for multiple Load calls to fill the Mentees List.
How can I optimise this method using best practice RavenDB syntax?
Edit
Thanks to #Jonah Himango (see accepted answer below) who solved the problem of multiple calls to the database for me. In addition I have also created a new extension method called 'Memoize' to eliminate the need for the external 'mentees' result List (see code above).
Here is the optimised code. Please feel free to comment and refine further.
The Linq
public static List<User> GetMentees(IDocumentSession db, string mentorId)
{
return db.Query<Relationship>()
.Customize(x => x.Include<Relationship>(o => o.MenteeId))
.Where(r => r.MentorId == mentorId)
.Memoize()
.Select(r => db.Load<User>(r.MenteeId))
.ToList();
}
The extension method
public static List<T> Memoize<T>(this IQueryable<T> target)
{
return target.ToList();
}
Note : This extension method may seem completely superfluous (it is really) but it irritates my geek-gland that I have to call a function called ToList(), not to create a list, but to force the execution of the Linq statement. So my extension method just renames ToList() to the far more accurate Memoize().
You'll want to use the .Include query customization to tell Raven to include the related user object off of each Relationship:
db.Query<Relationship>()
.Customize(x => x.Include<Relationship>(o => o.MenteeId))
.Where(r => r.MentorId == mentorId)
.Select(r => r.MenteeId)
.ForEach(id => mentees.Add(db.Load<User>(id))); // .Load no longer makes a call to the DB; it's already loaded into the session!
Relevant documentation here:
The call to Load() is resolved completely client side (i.e. without
additional requests to the RavenDB server) because the [related]
object has already been retrieved via the .Include call.
I have this structure:
class Foo {
IList<FooAttribute> Attributes { get; set; }
}
class FooAttribute {
bool IsSelected { get; set; }
string Value { get; set; }
}
And I have objects like:
IQuerable<Foo> foos; // Database repository object .AsQuerable()
IList<FooAttribute> attrs;
I need to filter only those items of foos that have all attributes of attrs list.
I tried this:
foos = foos.Where(foo =>
attrs.All(a =>
foo.Attributes.Any(at => at.Value == a)));
var filteredFoos = foos.ToList();
and i think it would work, but would be super slow and... it throws NotSupportedException...
By the way... I use ASP.NET MVC 3 and C# 4.0, so even the newest solutions are very welcome.
Thanks in advance.
FooAttribute fooAttributeAlias=null;
Session.QueryOver<Foo>().Inner.JoinAlias(x=>x.Attributes,()=>fooAttributeAlias)
.WhereRestrictionOn(()=>fooAttributeAlias).IsNotEmpty
.List();
I did not understand the query that you have written. I am not sure if the above query does what you expect, see the generated sql and see if it is correct.
Also what might help is the sql query that you expect to see which will give you the correct result.
i have the following lambda expression in MVC application.
var toprating= _db.Movie.SelectMany(m => m.Rating.Select(r=> new
{
movieID=r.MovieID,
MovieTitle= m.Title
})).GroupBy(m=>m.movieID).ToList();
ViewBag.TopMovie = toprating;
}
i want to pass this to my view.
i try writing the following in my view
IEnumerable<Movie> TopMovies = ViewBag.TopMovie;
but got this error
Cannot implicitly convert type 'object' to 'System.Collections.Generic.IEnumerable<Movie>'. An explicit conversion exists (are you missing a cast?)
any help will be appriciated.
i would recommend that you make a class that depicts your domain entity (Movie) like
public class MyMovie{
public int movieID { get; set; }
public string MovieTitle { get; set; }
}
and modify your linq query as
var toprating= _db.Movie.SelectMany(m => m.Rating.Select(r=> new MyMovie
{
movieID=r.MovieID,
MovieTitle= m.Title
})).GroupBy(m=>m.movieID).ToList();
ViewBag.TopMovie = toprating;
IEnumerable<MyMovie> TopMovies = ViewBag.TopMovie;
i have assumed that the Movie is your Domain entity, use view models to pass on to the views.
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