C# Generic Constraints not working correctly [closed] - c#

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I have the following code:
public interface IEnrollment
{
bool IsGood { get; set; }
}
public interface IEnrollmentToRegion
{
int RegionId { get; set; }
}
public class ByRegion : IEnrollmentToRegion
{
public int RegionId { get; set; }
}
public class Enrollment : IEnrollment
{
public bool IsGood { get; set; }
public ICollection<ByRegion> Regions { get; set; }
}
public class Main
{
public void DoSomething()
{
var e = new Enrollment();
if (isEnrolled(e, c => c.Any(l => l.RegionId == 10)))
{
}
}
private bool isEnrolled<T>(Enrollment enrollment, Func<ICollection<T>, bool> test) where T : IEnrollmentToRegion
{
return true;
}
}
What I'm trying to do is create the method isEnrolled that takes and object of the type IEnrollment and in this method I will do a bunch of checks to see if it return true or not. One of the things that I want to check is a collection of objects (in the above example it is simplified to only have 1 single class the ByRegion class, but in my real there are multiple Enrollment classes each with it's own separate collections under them that are of different types, but all of the types have a property called RegionId.
So I want to pass in a function that will check these various collections to see if the RegionId is in the collection. The problem that I'm having is that I get an error on the line
c.Any(l => l.RegionId == 10)) saying that it doesn't know what RegionId is. In fact when I hit the . after the l I do not get any intellisense drop down. I'm not sure why I don't get any dropdown because there is a restriction on T that T should be of the IEnrollmentToRegion type and that type has RegionId on it.


Your problem is that while a ByRegion is an IEnrollmentToRegion, an ICollection<ByRegion> is not a ICollection<IEnrollmentToRegion>. You can test this using reflection:
//Returns true
return typeof(IEnrollmentToRegion).IsAssignableFrom(typeof(ByRegion));
//Returns false
return typeof(ICollection<IEnrollmentToRegion>).IsAssignableFrom(typeof(ICollection<ByRegion>));
So you can't just specify T and let type inference take care of it for you. In fact, even if you specified the type explicitly, like:
isEnrolled<IEnrollmentToRegion>(e, c => c.Any(l => l.RegionId == 10))
You'd find that once you try to write the actual contents of isEnrolled<T>, you'd run into problems.
Here's an updated version of your code that works:
public interface IEnrollment<T> where T:IEnrollmentToRegion
{
bool IsGood { get; set; }
ICollection<T> Regions { get; set; }
}
public interface IEnrollmentToRegion
{
int RegionId { get; set; }
}
public class ByRegion : IEnrollmentToRegion
{
public int RegionId { get; set; }
}
public class Enrollment : IEnrollment<ByRegion>
{
public bool IsGood { get; set; }
public ICollection<ByRegion> Regions { get; set; }
}
public class Main
{
public void DoSomething()
{
var e = new Enrollment();
e.Regions = new List<ByRegion>() { new ByRegion { RegionId = 10 } };
if (isEnrolled(e, c => c.Any(l => l.RegionId == 10)))
{
//This line gets hit
}
}
private bool isEnrolled<T>(IEnrollment<T> enrollment, Func<ICollection<T>, bool> test) where T : IEnrollmentToRegion
{
return test(enrollment.Regions);
}

Related

AutoMapper - Inheritance preserve reference

I have the following scenario
Entity framework classes classes:
public class Block
{
public Guid Id { get; set; }
public ICollection<BlockLocation> BlockLocations { get; set; }
public BlockType Type { get; set; }
}
public class BlockLocation
{
public Guid Id { get; set; }
public Guid BlockId { get; set; }
public Block Block { get; set; }
}
And my Domain Entities look like
public class Block
{
public Block(BlockType type = BlockType.None) : this()
{
Type = type;
}
private Block() { }
public Guid Id { get; set; }
public List<BlockLocation> BlockLocations { get; set; }
public BlockType Type { get; set; }
}
public class LiveBlock : Block
{
public LiveBlock() : base(BlockType.Live) { }
}
public class UnsequencedBlock : Block
{
public UnsequencedBlock() : base(BlockType.Unsequenced) { }
}
public class BlockLocation
{
public Guid Id { get; set; }
public Guid BlockId { get; set; }
public Block Block { get; set; }
}
public enum BlockType
{
None = 0,
Live,
Unsequenced
}
And what I want to do is map from Entity Framework to a Domain entity to the child type and also preserve the reference so that I don't get a stack overflow
My mappings are
cfg.CreateMap<Data.Block, Domain.LiveBlock>();
cfg.CreateMap<Data.Block, Domain.UnsequencedBlock>();
cfg.CreateMap<Data.Block, Domain.Block>().PreserveReferences().ConstructUsing((block, context) =>
{
if (block.Type == BlockType.Live)
{
// This loops until stack overflow
return context.Mapper.Map<Domain.LiveBlock>(block);
}
if (block.Type == BlockType.Unsequenced)
{
return context.Mapper.Map<Domain.LiveBlock>(block);
}
return context.Mapper.Map<Domain.Block>(block);
});
cfg.CreateMap<Data.BlockLocation, Domain.BlockLocation>();
And I'm trying to do the following:
// This is the EF entity
var block = new Data.Block
{
Id = Guid.NewGuid(),
Type = BlockType.Live,
BlockLocations = new List<Data.BlockLocation>
{
new BlockLocation {Id = Guid.NewGuid()},
new BlockLocation {Id = Guid.NewGuid()}
}
};
block.BlockLocations[0].Block = block;
block.BlockLocations[1].Block = block;
// Trying to create a Domain entity
var domainBlock = Mapper.Map<Data.Block, Domain.Block>(block);
The result that I want to achieve is for domainBlock to be of type LiveBlock and have a list of BlockLocations which in turn have the same LiveBlock entity as their Block property
What I get is a loop in ConstructUsing, until I get stack overflow.
Now, my questions are:
Can this be achieved with AutoMapper?
If yes, can it be done with ContructUsing? I've also tried ConvertUsing, but I get the same result.
Some other approach maybe?
I know that a way of doing to would be to Ignore the BlockLocations property from Domain.Block and map them separately, but I would like to have Automapper to that automatically.
Thank you for your help.

Got it working with Lucian's help
I changed the mapper to the following
cfg.CreateMap<Data.Block, Domain.LiveBlock>().PreserveReferences();
cfg.CreateMap<Data.Block, Domain.UnsequencedBlock>().PreserveReferences();
cfg.CreateMap<Data.Block, Domain.Block>().PreserveReferences().ConstructUsing((block, context) =>
{
if (block.Type == BlockType.Live)
{
var b = new LiveBlock();
return context.Mapper.Map(block, b, context);
}
if (block.Type == BlockType.Unsequenced)
{
var unsequencedBlock = new UnsequencedBlock();
return context.Mapper.Map(block, unsequencedBlock, context);
}
return context.Mapper.Map<Domain.Block>(block);
});
cfg.CreateMap<Data.BlockLocation, Domain.BlockLocation>().PreserveReferences();
The secred was usint the Map method that takes the context as a parameter
context.Mapper.Map(block, unsequencedBlock, context);

Entity Framework - Mapped property will not populate, despite being retrieved by SQL

I'm trying to add a new sub-entity, product component ProductRevComp to an existing entity ProductRev. However when I retrieve an instance of the ProductRev class, the Comps collection is never populated (even when explicitly Including() it). I BELIEVE I have mapped everything correctly, but it has taken more fiddling than I want and this is the most likely place for a mistake to be hiding. However profiling the SQL statements show the relevent columns are being populated with the correct data.
Checking db.ProductRevComps (i.e. the DbSet of all my comps) shows the records can be loaded, and that mapping is working as expected.
Mappings:
public class ProductRevConfiguration : EntityTypeConfiguration<ProductRev>
{
public ProductRevConfiguration()
{
HasKey(p => p.ProductRevId);
HasMany(p => p.Comps).WithRequired().HasForeignKey(p => p.ParentProductRevId);
Ignore(p => p.ProgrammedParts);
}
}
public class ProductRevCompConfiguration : EntityTypeConfiguration<ProductRevComp>
{
public ProductRevCompConfiguration()
{
HasKey(p => new { p.ParentProductRevId, p.CompProductRevId });
HasRequired(p => p.ParentProductRev).WithMany().HasForeignKey(p => p.ParentProductRevId);
HasRequired(p => p.CompProductRev).WithMany().HasForeignKey(p => p.CompProductRevId);
}
}
Product entity (amazingly simplified):
public class ProductRev
{
public string ProductRevId { get; set; }
public virtual List<ProductRevComp> Comps { get; set; }
public virtual List<ProductRevComp> ProgrammedParts { get { return Comps; } }//Will be filtered once I get this working
public ProductRev() { }
}
Comp entity:
public class ProductRevComp
{
public string ParentProductRevId { get; set; }
public virtual ProductRev ParentProductRev { get; set; }
public string CompProductRevId { get; set; }
public virtual ProductRev CompProductRev { get; set; }
public int CompTypeValue { get; set; }
public ProductRevCompType CompType
{
get { return (ProductRevCompType)CompTypeValue; }
set { CompTypeValue = (int)value; }
}
public enum ProductRevCompType { ProgrammedPart = 1 };
public ProductRevComp() { }
public override string ToString()
{
return base.ToString();
}
}
Removing the extra prog parts collection doesn't change anything.
How can I get the ProductRev entity to populate the Comps property without resorting to a manual DB hit?
(Must run as the office is closing and I don't have a key - I hope I have included all details, please comment if anything is missing.)

Dynamic cast behavior in loop

I'm trying to accomplish some hacking & slashing and was wondering how to approach the following.
There are 2 interfaces defined:
public interface IBase
{
string Name { get; }
void Run();
}
public interface ISecondBase<T> : IEntityTask
{
Thing<T> Thing { get; }
}
Somewhere else I have a list of IBase.
This list is filled ISecondBase. I would like to be able to loop through the list of Base, but using some reflection tricks and hacks als be able to call Thing on the items. I know they're there, the compiler doesn't.
So I'd have to cast it to its concrete type at runtime, but this cast has to be dynamic, based on reflected information in the loop... So all type information is dynamic... I'm starting to think in circles :)
Since I know on beforehand that everything inside it is always of the SecondBase type, I decided to use the dynamic keyword and just let it resolve at runtime. This seems to me like an easy way out. Is there some best practice for these cases? Should I redesign, without loss of generality, and how?
foreach(var x in y)
{
dynamic melp = x;
melp.Thingy;
}
Where to start?
Edit: Perhaps some more code to make the example less contrived.
I have the base classes as mentioned. In real life they look like this:
public interface IEntityTask
{
string Name { get; }
void Run();
}
public interface IEntityTask<T> : IEntityTask
{
Task<T> Task { get; }
}
//Then there are classes that implement these:
public class CreateEntityTask<T> : IEntityTask<Guid>
{
public T Entity { get; private set; }
public Func<T, Guid> EntityMethod { get; private set; }
public Task<Guid> Task { get; private set; }
public void Run()
{
Task = Task<Guid>.Run(() => entityAccess.CreateEntity<T>(Entity, EntityMethod));
}
}
public class ReadEntityTask<T> : IEntityTask<T>
{
public Guid EntityId { get; private set; }
public Func<Guid, T> EntityMethod { get; private set; }
public Task<T> Task { get; private set; }
public void Run()
{
Task = Task<T>.Run(() => entityAccess.ReadEntity<T>(EntityId, EntityMethod));
}
}
//Furthermore there is a class called EntityTaskManager, which holds a list of these things and runs, awaits & collects the results on them.
public class EntityTaskManager
{
public List<IEntityTask> EntityTasks { get; set; } // I want tasks of Guid and bool in here!!!!
public Dictionary<string, object> EntityTaskResults { get; set; }
}
In a calling class I construct a new EntityTask and add it to the list. And then call RunTasks on the manager.

I'd modify IEntityTask like this:
public interface IEntityTask
{
string Name { get; }
void Run();
object Result { get; }
}
If EntityTaskManager is the only place, where you work with IEntityTask type, the implementation of Result would be explicit:
public class CreateEntityTask<T> : IEntityTask<Guid>
{
/* The rest of code here */
object IEntityTask.Result
{
get { return Task.Result; }
}
}
Then fetching task results should be trivial:
var results = entityTasksManager
.EntityTasks
.Select(t => t.Result);

Joining two lists of different types and sort them by date

I have a first list of entities like this :
public partial class Networking :EntityBase
{
public virtual int NetWorkingId
{
get;
set;
}
public virtual string NetWorkingParam
{
get;
set;
}
public virtual System.DateTime NetWorkingDate
{
get;
set;
}
}
And I have a second list of entities like this:
public partial class PrivateNetwork :EntityBase
{
public virtual int PrivateNetworkId
{
get;
set;
}
public virtual int ContaId
{
get { return _contaId; }
set
{
if (_contaId != value)
{
if (Contact != null && Contact.ContaId != value)
{
Contact = null;
}
_contaId = value;
}
}
}
public virtual Nullable<System.DateTime> DateCreation
{
get;
set;
}
}
I want to collect these two lists in one and sort all the elements by date.
Is that possible ?

You can do this, although it's not very pretty, and you end up with an IEnumerable<object> so you have to check each item's type before you can use it:
IEnumerable<object> sorted = myNetworkingList
.Concat<object>(myPrivateNetworkList)
.OrderBy(n => n is Networking
? (DateTime?)((Networking)n).NetWorkingDate
: ((PrivateNetwork)n).DateCreation);
foreach (object either in sorted)
{
if (either is Networking)
// Networking; do something
else
// PrivateNetwork; do something else
}

This problem could easily be solved by using polymorphism; use a common base class or interface for both classes, which has the DateTime property you want to sort on.
Example:
public abstract class NetworkingBase : EntityBase
{
public DateTime DateToSortOn { get; set; }
}
or
public interface INetworking
{
public DateTime DateToSortOn { get; set; }
}
And then make your classes derive from NetworkingBase or implement INetworking:
public partial class Networking : NetworkingBase
{
...
}
public partial class PrivateNetwork : NetworkingBase
{
...
}
or
public partial class Networking : EntityBase, INetworking
{
...
}
public partial class PrivateNetwork : EntityBase, INetworking
{
...
}
Do a LINQ Union or Concat and then an OrderBy on the resulting collection.

What I should have asked earlier is . . .
What do you want to do after you've sorted them?
The answer to this could have a big impact on the potential solution.
If the answer is something like I need to display a list of the dates, where you only need the dates in order. If so then you don't need to merge the two lists, you can get a sequence of just the ordered dates and use that e.g.
var orderedDates = networks.Select(n => n.NetworkingDate)
.Union(privateNetworks.Select(n => n.DateCreation))
.OrderBy(date => date);
If the answer is I need to display a list of links showing the Date that links to the Id of the object, and something to identify the type of object, then you could get away with something very like the above, with an Anonymous object.
var orderedDates = networks.Select(n => new {Date = n.NetworkingDate, Id = n.NetWorkingId, NetworkType = n.GetType().Name})
.Union(privateNetworks.Select(n => new {Date = n.DateCreation, Id = n.PrivateNetWorkingId, NetworkType = n.GetType().Name}))
.OrderBy(n => n.Date);
However if the answer is I need to send a Shutdown() command to the 10 oldest networks then you really do need a polymorphic solution, where you have a single type that you can call a Shutdown() method on, that will resolve to the specific Shutdown() method on the types you're using.
A Polymorphic solution to use only if user khellang's answer doesn't work for you
From a comment on another answer
#BinaryWorrier I chose this answer because I already have records in
the database, so if I choose to add a new interface how will I deal
with the records already stored before adding the interface ?
I find it difficult to believe that your ORM won't allow you to add an interface to an entity class and not - somehow - mark that interface and/or it's member so they're ignored by the ORM.
However, assuming you can't add a new interface or base class, you can still do this polymorphically.
Add the interface, add a class implementing the interface that for each of your Network classes (the Abstractor classes), then transform the network classes into Abstractor classes, adding them to a List<INetwork> and sorting that list.
public interface INetwork
{
DateTime? Date { get; }
}
public class PrivateNetworkAbstractor
:INetwork
{
private PrivateNetwork network;
public PrivateNetworkAbstractor(PrivateNetwork network)
{
this.network = network;
}
public DateTime? Date
{
get { return network.DateCreation; }
}
}
public class NetworkingAbstractor
: INetwork
{
private Networking networking;
public NetworkingAbstractor(Networking networking)
{
this.networking = networking;
}
public DateTime? Date
{
get { return networking.NetWorkingDate; }
}
}
...
public IEnumerable<INetwork> MergenSort(IEnumerable<Networking> generalNetWorks, IEnumerable<PrivateNetwork> privateNetWorks)
{
return generalNetWorks.Select(n => new NetworkingAbstractor(n)).Cast<INetwork>()
.Union(privateNetWorks.Select(n => new PrivateNetworkAbstractor(n)).Cast<INetwork>())
.OrderBy(n=> n.Date);
}

Create an interface that has the date and implement in in both classes. After that sorting is easy.
public interface INetwork
{
DateTime? Date { get; }
}
public partial class Networking :EntityBase, INetwork
{
public DateTime? Date
{
get { return NetWorkingDate; }
}
}
public partial class PrivateNetwork :EntityBase, INetwork
{
public DateTime? Date
{
get { return DateCreation; }
}
}
var commonList = new List<INetwork>();
// Add instances of PrivateNetwork and Networking to the list
var orderedByDate = commonList.OrderBy(n => n.Date);

First solution is using anonymous type
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Example1
{
class Program
{
class Human
{
public string Name { get; set; }
public string Hobby { get; set; }
public DateTime DateOfBirth { get; set; }
}
class Animal
{
public string Name { get; set; }
public string FavouriteFood { get; set; }
public DateTime DateOfBirth { get; set; }
}
static void Main(string[] args)
{
var humans = new List<Human>
{
new Human
{
Name = "Kate",
Hobby = "Fitness",
DateOfBirth = DateTime.Now.AddYears(-27),
},
new Human
{
Name = "John",
Hobby = "Cars",
DateOfBirth = DateTime.Now.AddYears(-32),
},
};
var animals = new List<Animal>
{
new Animal
{
Name = "Fluffy",
FavouriteFood = "Grain",
DateOfBirth = DateTime.Now.AddYears(-2),
},
new Animal
{
Name = "Bongo",
FavouriteFood = "Beef",
DateOfBirth = DateTime.Now.AddYears(-6),
},
};
var customCollection = (from human in humans
select new
{
Name = human.Name,
Date = human.DateOfBirth,
}
).Union(from animal in animals
select new
{
Name = animal.Name,
Date = animal.DateOfBirth,
}).OrderBy(x => x.Date);
foreach (dynamic customItem in customCollection)
Console.WriteLine(String.Format("Date: {0}, Name: {1}", customItem.Date, customItem.Name));
Console.Read();
}
}
}
or without anonymous type (created CustomClass):
...
class CustomClass
{
public string Name { get; set; }
public DateTime Date { get; set; }
}
...
var customCollection = (from human in humans
select new CustomClass
{
Name = human.Name,
Date = human.DateOfBirth,
}
).Union(from animal in animals
select new CustomClass
{
Name = animal.Name,
Date = animal.DateOfBirth,
}).OrderBy(x => x.Date);
foreach (CustomClass customItem in customCollection)
Console.WriteLine(String.Format("Date: {0}, Name: {1}", customItem.Date, customItem.Name));
...

I simply added a base class and assigned it as the parent of both list's classes . and then simple did the union . it made the trick

How to work with multiple DbSets with common base class in EF 5?

I have 2 POCO classes:
class Email: Base
{
public int SomeProperty { get; set; }
}
class Photo: Base
{
public int SomeOtherProperty { get; set; }
}
and a base class
abstract class Base
{
public DateTime DateCreated { get; set; }
}
here is my context definition:
public class EntitiesContext : DbContext
{
public DbSet<Email> Emails { get; set; }
public DbSet<Photo> Photos { get; set; }
}
of course these classes here are just for the sake of example, things are quite more complicated.
base class is only intended to have common properties for each table - date modified, state, etc. I believe I use Table-Per-Type approach.
PROBLEM: I have some common business logic which I need to run against each table (for example, count non-processed items of each type). I need a way to iterate through a set of tables with common base class. I was hoping to do something like this:
private void GoThroughAllTables(Action<DbSet<Base>> fnProcess, bool needSave)
{
using (var db = new EntitiesContext())
{
fnProcess(db.Emails);
fnProcess(db.Photos);
if (needSave == true)
{
db.SaveChanges();
}
}
}
public IEnumerable<QueueStatus> GetQueueStatus()
{
var res = new List<QueueStatus>();
GoThroughAllTables((set) =>
{
res.Add(new QueueStatus
{
Count = set.Cast<Base>().Count(x => x.DateCreated > someDate),
});
}, false);
return res;
}
public void DeleteFailedItems()
{
GoThroughAllTables((set) =>
{
set.Cast<Base>().Remove(x => x.DateCreated > someDate);
}, true);
return res;
}
this will not compile:
fnProcess(db.Emails);
Argument 1: cannot convert from 'System.Data.Entity.DbSet|Email|' to
'System.Data.Entity.DbSet|Base|'
passing non-typed DbSet will not work because Cast will fail.
so I'm not sure what else can I try. Any suggestions?

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