There is something I don't fully understand with the code bellow. I'm trying to find the workers that have a duplicate module in their modules collection.
Here's the entities (simplified for the sake of brevity):
public class Worker
{
public int Id { get; private set; }
public ICollection<TakenTrainingModule> TakenTrainingModules { get; private set; }
public Worker()
{
TakenTrainingModules = new HashSet<TakenTrainingModule>();
}
}
public class TakenTrainingModule
{
public int Id { get; set; }
public int TrainingModuleId { get; set; }
}
And here's the query:
var query = from worker in _context.Workers.Include(worker => worker.TakenTrainingModules)
let distinctModules = worker.TakenTrainingModules.Select(module => module.TrainingModuleId).Distinct()
where worker.TakenTrainingModules.Count != distinctModules.Count()
select worker;
With the query bellow, the returned workers have their TakenTrainingModules collection empty.
But, with the next query (without using the keywork let), the collection is fully and correctly loaded:
var query = from worker in _context.Workers.Include(worker => worker.TakenTrainingModules)
where worker.TakenTrainingModules.Count != worker.TakenTrainingModules.Select(module => module.TrainingModuleId).Distinct().Count()
select worker;
What am I missing? Is the let keyword first executing the distinct query and fools the object state manager that the module are loaded but they aren't and the selector doesn't load them next?
Any explanations welcome! :-)
I've updated the query as this:
var query = from worker in _context.Workers
let distinctModules = worker.TakenTrainingModules.Select(module => module.TrainingModuleId).Distinct()
where worker.TakenTrainingModules.Count != distinctModules.Count()
select worker;
return query.Include(worker => worker.TakenTrainingModules).ToArray();
And everything is fine. Thanks to Dismissile for pointing me out a nice answer.
Related
I want to write a simple query, but there are some problems.
I have 2 tables M to N:
Users -> Events.
I want to get all users of a specific event (get this event by eventId).
public IQueryable<User> GetUsersByEventId(int eventId)
{
IQueryable<User> query = this.Context.Users.AsQueryable();
return query.Where(x => x.Events.SingleOrDefault(e => e.EventId == eventId)); ??
}
Something is missing and I dont know what, can someone help me? Thanks a lot !
If I understand you correctly (adding your models would help), I think you want Any
public IQueryable<User> GetUsersByEventId(int eventId)
{
return Context.Users
.Where(u => u.Events.Any(e => e.EventId == eventId));
}
This should return all users who have any event matching the given id.
Note: If you set up your relationships correctly, you should be able to get this directly from the Event.
public class Event
{
...
public virtual ICollection<User> Users { get; set; }
}
So then, you'd get the Event by id and access it's user collection.
var evt = repo.GetEventById(id);
var users = evt.Users;
I suggest you do that in your Event model itself. AFAIK you are using Event, User and EventUsers tables which is standard stuff for many2many.
public class Event
{
public int Id { get; set; }
// ...
public virtual ICollection<EventUsers> EventUsers { get; set; } // This is table that holds EventId, UserId (many2many)
public IQueryable<User> Users { get { return this.EventUsers.Select(x => x.User); } } // Get all users that are in this event
}
I am using ASP.NET MVC 3 with Entity Framework 4 using POCOs and want to query a set and select some properties to put into my viewModel. I will sketch a simplified version of my situation:
Situation:
I have an entity BananaTree containing a collection of Banana
public class Banana
{
public int Id { get; set; }
public int Size { get; set; }
public TimeSpan Age { get; set }
public string Description { get; set; }
}
public class BananaTree
{
public int Id { get; set; }
public ICollection<Banana> Bananas { get; set; }
}
I also have a view model BananaListItemViewModel used in the view showing a list of bananas for a certain banana tree. This view is managed by the BananaTreeController
public class BananaListItemViewModel
{
public int Id { get; set; }
public TimeSpan Age { get; set }
}
I have a Details action on the controller like so:
public ActionResult Details(int bananaTreeId)
{
var viewModel = from bananaTree in bananaTreeRepository.BananaTrees
where bananaTree.Id == bananaTreeId
from banana in bananaTree.Bananas
select new BananaListItemViewModel
{
Id = banana.Id,
Age = banana.Age
};
return View(viewModel);
}
What I want to change
This works fine and now I only select the items from the database that I need for my view model. However, I want to take out some more logic from my controller and am trying to do this as much as possible.
I would like to have a function in my repository like so:
IQueryable<Banana> GetBananas(int bananaTreeId)
{
return (from bananaTree in BananaTrees
where bananaTree.Id == bananaTreeId
select bananaTree.Bananas).Single().AsQueryable();
}
and use it like so:
public ActionResult Details(int bananaTreeId)
{
var viewModel = from banana in bananaTreeRepository.GetBananas(bananaTreeId)
select new BananaListItemViewModel
{
Id = banana.Id,
Age = banana.Age
};
return View(viewModel);
}
Question
My question is, in this case, will the two queries be combined and go to the database in one go like in my first example or will this first get all the bananas from the tree completely out of the database and perform the second query on that list? I would prefer the first case. If not, could I rewrite the GetBananas query to get that behaviour (for example like the query below)?
IQueryable<Banana> GetBananas(int bananaTreeId)
{
return from bananaTree in BananaTrees
where bananaTree.Id == bananaTreeId
from banana in bananaTree.Bananas
select banana;
}
Thanks very much in advance.
In your specific case, it will be only one query, if the call to Single() doesn't lead to the query to be executed. Unfortunately, I couldn't find any info on whether it does or does not. The call to AsQueryable does not trigger the execution as long, as the Bananas property really is an IQueryable.
According to http://msdn.microsoft.com/en-us/library/bb156472.aspx, the call to Single doesn't execute your query.
Conclusion:
You code should result in only one query.
In general:
You can pass an IQueryable from one method to another without it being implicitly executed.
The following code will result in only one SQL statement executed at the end, when the call to ToList happens:
IQueryable<Banana> GetBananasByWeight(int weight)
{
return from banana in Bananas where banana.Weight = weight;
}
IQueryable<Banana> FilterByQuality(IQueryable<Banana> bananaQuery, int quality)
{
return bananaQuery.Where(b => b.Quality == quality);
}
public List<Banana> GetBananas(int weight, int quality)
{
var query = GetBananasByWeight(weight);
var filteredBananas = FilterByQuality(query, quality);
return filteredBananas.ToList();
}
I have an TaxWork entity which is persisted using NHibernate. This entity has the following properties (among others):
public virtual TaxWorkType Type { get; set; } //Kctc.TaxWorkType is an enumeration
public virtual TaxWorkStatus Status { get; set; } //Kctc.TaxWorkStatus is an enumeration
public virtual LegalWorkPriority Priority { get; set; } //Kctc.LegalWorkType is an enumeration
public virtual User Handler { get; set; } //Kctc.BusinessLayer.Entities.User is another entity
public virtual int? CaseNumber { get; set; }
I am using Linq to NHibernate to pull of a subset of the tax work objects as follows (taxWorkRepository.All obviously returns an IQueryable):
foreach (TaxWork taxWork in taxWorkRepository.All.Where(x => x.CaseNumber == _caseNumber).OrderBy(x => x.DateCreated))
{
...
}
This works fine. I want to use projection in order to query only the columns that are required in this case. I am usnig the following code:
foreach (var taxWorkFragment in taxWorkRepository.All.Where(x => x.CaseNumber == _caseNumber).OrderBy(x => x.DateCreated).Select(x => new { Type = x.Type, DateCreated = x.DateCreated, Handler = x.Handler, Status = x.Status, Priority = x.Priority }))
{
...
}
However, I'm getting the following error when trying to create the anonymous type:
Invalid cast from 'Kctc.TaxWorkStatus' to 'Kctc.BusinessLayer.Entities.User'.
Where on earth is it getting the idea that it should be casting a TaxWorkStatus to a User?
Any suggestions whatsoever what might be going wrong?
Try to make like this:
foreach (var taxWorkFragment in taxWorkRepository.All.Where(x => x.CaseNumber == _caseNumber).OrderBy(x => x.DateCreated)
.Select(x => new TaxWork { Type = x.Type, DateCreated = x.DateCreated, Handler = x.Handler, Status = x.Status, Priority = x.Priority }))
{
...
}
It should help
I have two ILIst of these objects:
class ProductionMachineType
{
string code { get; set; }
IEnumerable<string> ProductionToolsLink { get; set; }
}
class ProductionTools
{
string code { get; set; }
}
I am looking for a fast Linq method that make me able to query the IList<ProductionMachineType> that contains at least one ProductionToolsLink contained inside the ILIst<ProductionTools>.
In SQL I would wite something like this:
SELECT
*
FROM
IList<ProductionMachineType>
WHERE
IList<ProductionMachineType>.ProductionToolsLink IN ILIst<ProductionTools>
Is there a way to do this?
Contains method can help you:
var names = new string[] { "Alex", "Colin", "Danny", "Diego" };
var matches = from person in people
where names.Contains(person.Firstname)
select person;
This will do it, but I can't guarantee how efficient it is...
var output = machines.Where(machine =>
machine.ProductionToolsLink
.Any(link => tools.Select(tool => tool.code).Contains(link)));
The basic problem...
I have a method which executes the following code:
IList<Gig> gigs = GetGigs().WithArtist(artistId).ToList();
The GetGigs() method gets Gigs from my database via LinqToSql...
So, when GetGigs().WithArtist(artistId).ToList() is executed I get the following exception:
Member access 'ListenTo.Shared.DO.Artist Artist' of 'ListenTo.Shared.DO.Act' not legal on type 'System.Collections.Generic.List`1[ListenTo.Shared.DO.Act]
Note that the extension function "WithArtist" looks like this:
public static IQueryable<Gig> WithArtist(this IQueryable<Gig> qry, Guid artistId)
{
return from gig in qry
where gig.Acts.Any(act => (null != act.Artist) && (act.Artist.ID == artistId))
orderby gig.StartDate
select gig;
}
If I replace the GetGigs() method with a method that constructs a collection of gigs in code (rather than from the DB via LinqToSQL) I do NOT get the exception.
So I'm fairly sure the problem is with my LinqToSQl code rather than the object structure.
However, I have NO IDEA why the LinqToSQl version isnt working, so I've included all the associated code below. Any help would be VERY gratefully receivced!!
The LinqToSQL code....
public IQueryable<ListenTo.Shared.DO.Gig> GetGigs()
{
return from g in DBContext.Gigs
let acts = GetActs(g.ID)
join venue in DBContext.Venues on g.VenueID equals venue.ID
select new ListenTo.Shared.DO.Gig
{
ID = g.ID,
Name = g.Name,
Acts = new List<ListenTo.Shared.DO.Act>(acts),
Description = g.Description,
StartDate = g.Date,
EndDate = g.EndDate,
IsDeleted = g.IsDeleted,
Created = g.Created,
TicketPrice = g.TicketPrice,
Venue = new ListenTo.Shared.DO.Venue {
ID = venue.ID,
Name = venue.Name,
Address = venue.Address,
Telephone = venue.Telephone,
URL = venue.Website
}
};
}
IQueryable<ListenTo.Shared.DO.Act> GetActs()
{
return from a in DBContext.Acts
join artist in DBContext.Artists on a.ArtistID equals artist.ID into art
from artist in art.DefaultIfEmpty()
select new ListenTo.Shared.DO.Act
{
ID = a.ID,
Name = a.Name,
Artist = artist == null ? null : new Shared.DO.Artist
{
ID = artist.ID,
Name = artist.Name
},
GigId = a.GigID
};
}
IQueryable<ListenTo.Shared.DO.Act> GetActs(Guid gigId)
{
return GetActs().WithGigID(gigId);
}
I have included the code for the Act, Artist and Gig objects below:
public class Gig : BaseDO
{
#region Accessors
public Venue Venue
{
get;
set;
}
public System.Nullable<DateTime> EndDate
{
get;
set;
}
public DateTime StartDate
{
get;
set;
}
public string Name
{
get;
set;
}
public string Description
{
get;
set;
}
public string TicketPrice
{
get;
set;
}
/// <summary>
/// The Act object does not exist outside the context of the Gig, therefore,
/// the full act object is loaded here.
/// </summary>
public IList<Act> Acts
{
get;
set;
}
#endregion
}
public class Act : BaseDO
{
public Guid GigId { get; set; }
public string Name { get; set; }
public Artist Artist { get; set; }
}
public class Artist : BaseDO
{
public string Name { get; set; }
public string Profile { get; set; }
public DateTime Formed { get; set; }
public Style Style { get; set; }
public Town Town { get; set; }
public string OfficalWebsiteURL { get; set; }
public string ProfileAddress { get; set; }
public string Email { get; set; }
public ImageMetaData ProfileImage { get; set; }
}
public class BaseDO: IDO
{
#region Properties
private Guid _id;
#endregion
#region IDO Members
public Guid ID
{
get
{
return this._id;
}
set
{
this._id = value;
}
}
}
}
I think the problem is the 'let' statement in GetGigs. Using 'let' means that you define a part of the final query separately from the main set to fetch. the problem is that 'let', if it's not a scalar, results in a nested query. Nested queries are not really Linq to sql's strongest point as they're executed deferred as well. In your query, you place the results of the nested query into the projection of the main set to return which is then further appended with linq operators.
When THAT happens, the nested query is buried deeper into the query which will be executed, and this leads to a situation where the nested query isn't in the outer projection of the query to execute and thus has to be merged into the SQL query ran onto the DB. This is not doable, as it's a nested query in a projection nested inside the main sql query and SQL doesn't have a concept like 'nested query in a projection', as you can't fetch a set of elements inside a projection in SQL, only scalars.
I had the same issue and what seemed to do the trick for me was separating out an inline static method call that returned IQueryable<> so that I stored this deferred query into a variable and referenced that.
I think this is a bug in Linq to SQL but at least there is a reasonable workaround. I haven't tested this out yet but my assumption is that this problem may arise only when referencing static methods of a different class within a query expression regardless of whether the return type of that function is IQueryable<>. So maybe it's the class that holds the method that is at the root of the problem. Like I said, I haven't been able to confirm this but it may be worth investigating.
UPDATE: Just in case the solution isn't clear I wanted to point it out in context of the example from the original post.
public IQueryable<ListenTo.Shared.DO.Gig> GetGigs()
{
var acts = GetActs(g.ID); // Don't worry this call is deferred
return from g in DBContext.Gigs
join venue in DBContext.Venues on g.VenueID equals venue.ID
select new ListenTo.Shared.DO.Gig
{
ID = g.ID,
Name = g.Name,
Acts = new List<ListenTo.Shared.DO.Act>(acts),
Description = g.Description,
StartDate = g.Date,
EndDate = g.EndDate,
IsDeleted = g.IsDeleted,
Created = g.Created,
TicketPrice = g.TicketPrice,
Venue = new ListenTo.Shared.DO.Venue {
ID = venue.ID,
Name = venue.Name,
Address = venue.Address,
Telephone = venue.Telephone,
URL = venue.Website
}
};
}
Note that while this should correct the issue at hand there also seems to be another issue in that the deferred acts query is being accessed in each element of the projection which I would guess would cause separate queries to be issued to the database per row in the outer projection.
I don't see anything in your classes to indicate how LINQ to SQL is meant to work out which column is which, etc.
Were you expecting the WithArtist method to be executed in .NET, or converted into SQL? If you expect it to be converted into SQL, you'll need to decorate your Gig class with appropriate LINQ to SQL attributes (or configure your data context some other way). If you want it to be executed in code, just change the first parameter type from IQueryable<Gig> to IEnumerable<Gig>.
I found out that an issue like this (which I also had recently) can be resolved, if you convert the IQueryable (or Table) variable Gigs into a list like so
return from g in DBContext.Gigs.ToList()
...
If that still doesn't work, do the same for all the IQueryables. The reason behind seems to me that some queries are too complex to be translated into SQL. But if you "materialize" it into a list, you can do every kind of query.
Be careful, you should add "filters" (where conditions) early because too much memory consumption can become a problem.