I have this problem with lists and I can't seem to fix it
I have this class that implement a interface that has the following method.
public List<T> CalculateWad<T, TH>(
List<T> outputList,
List<TH> inputList,
bool flag)
{
...
}
Now, I have a outputlist and a inputlist with a common field Contract. I need to delete in outputlist all contracts that exist in inputlist.
It has to be as generic as possible. I can't seem to be able to get the fields of the lists.
Any ideas?
In order to access the Contract property, the generics T and TH must implement an interface with the Contract property.
Documentation : where (generic type constraint) (C# Reference)
interface IContractable { string Contract { get; } }
Then your class containing the CalculateWad method must be define as follow :
class MyClass<T, TH>
where T : IContractable
where TH : IContractable
{
public List<T> CalculateWad(List<T> outputList, List<TH> inputList, bool flag)
{
return outputList
.Where(o =>
inputList.Select(i => i.Contract).Contains(o.Contract) == false)
.ToList();
}
}
This should to the job, by adding a common IHasContract interface that both T and TH must implement:
class Program
{
static void Main(string[] args)
{
}
private IList<T> CalculateWad<T, TH>(IList<T> output,
IList<TH> input, bool flag)
where T : IHasContract
where TH : IHasContract
{
var contracts = new HashSet<string >(input.Select(i => i.Contract));
var qry = from o in output
where !contracts.Contains(o.Contract)
select o;
return qry.ToList();
}
private sealed class Contract
{
}
private interface IHasContract
{
string Contract { get; }
}
private sealed class Foo : IHasContract
{
public string Contract { get; set; }
}
private sealed class Bar : IHasContract
{
public string Contract { get; set; }
}
}
Note that is does not modify output, which you mention in the text. It does, however, return a new altered copy of the list, which may be rather what the method signature describes.
So this is your interface:
public List CalculateWad( List outputList, List inputList, bool flag) {
...
}
And you need to do this? Assumes that the objects in each list can be compared by their equals method.
public List<T> CalculateWad<T, TH>( List<T> outputList, List<TH> inputList, bool flag) {
// cast list to be regular object lists
List out = (List) outputList;
List in = (List) inputList;
for(Object object : in){
out.remove(object); // this looks for an object that matches using contract.equals(object)
}
}
What is flag variable for?
Related
In my Data access layer, I am calling the GET method with the following Lambda expression :
public List<T> Get<T>() where T : class
{
var list = Context.Set<T>().ToList().Distinct().Where(x => x.Content_type == "Test");
return list;
}
But getting error
"Cannot resolve symbol Content_type"
How can i resolve this issue ?
The problem is that Content_type is not a part of T class because it's just a class.
As #tchelidze says, you can set a where clause on your function to specify a type, like this :
public List<T> Get<T>() where T : IYourCommonInterface
{
var list = Context.Set<T>().Where(x => x.Content_type == "Test").Distinct().ToList();
return list;
}
But if you need to be totaly generic, you can add a selector to your function like this :
public List<T> Get<T>(Func<T, object> selector) where T : class
{
var list = Context.Set<T>().Where(x => selector(x) == "Test").Distinct().ToList();
return list;
}
And use it like that :
Get(x => x.Content_type);
Also, if you want to go further, you can pass the entire condition :
public List<T> Get<T>(Func<T, bool> condition) where T : class
{
var list = Context.Set<T>().Where(condition).Distinct().ToList();
return list;
}
And use it like this :
Get(x => x.Content_type == "test");
Hope it helps.
Reason is that all you know about T is that it is a class. You do not know if it contains Content_type property or not.
If you always pass T class which contains definition for Content_type try following .
Context.Set<T>().ToList().Distinct().Where(x => (x as SomeClassWithContentTypeField).Content_type == "Test");
Better way will be if you introduce interface IHasContentTypeField which declared Content_type property
public interface IHasContentTypeField
{
string Content_type { get; set; }
}
then constraint T to this interface.
public List<T> Get<T>() where T : IHasContentTypeField
Then you can implement IHasContentTypeField in classes for which you want to call Get<T> method.
public class A : IHasContentTypeField
{
public string Content_type { get; set; }
}
I need to have a CRUd operations on my class (CompetenceSpecific).
Competence has three derived classes - CompetenceFunction, CompetenceArea and CompetenceSpecifc
The error I recieved:
There are no EntitySets defined for the specified entity type 'CompetencyManagement.Domain.Entities.CompetenceFunction'. If 'CompetencyManagement.Domain.Entities.CompetenceFunction' is a derived type, use the base type instead. Parameter name: TEntity
How should I correct this? Please suggest a solution that would solve my problem. Thanks
Please check the code below, I removed some parts of the code for simplicity.
--MODEL
public class Competence
{
public int CompetenceID { get; set; }
public int CourseID { get; set; }
...
}
public class CompetenceFunction : Competence
{
}
--REPOSITORY and interfaces
public interface IRepository<T> where T : class
{
T GetById(object id);
IEnumerable<T> GetAll();
IEnumerable<T> Query(Expression<Func<T, bool>> filter);
void Add(T entity);
void Remove(T entity);
}
public abstract class Repository<T> : IRepository<T>
where T : class
{
protected IObjectSet<T> _objectSet;
public Repository(ObjectContext context)
{
_objectSet = context.CreateObjectSet<T>();
}
...
}
public class CompetenceFunctionRepository : Repository<CompetenceFunction>
{
public CompetenceFunctionRepository(ObjectContext context)
: base(context)
{
}
public override CompetenceFunction GetById(object id)
{
return _objectSet.SingleOrDefault(s => s.CompetenceID == (int)id);
}
}
--UNIT oF WORK
public interface IUnitOfWork
{
IRepository<CompetenceFunction> CompetenceFunctions { get; }
IRepository<CompetenceArea> CompetenceAreas { get; }
IRepository<CompetenceSpecific> CompetenceSpecifics { get; }
void Commit();
}
public class UnitOfWork : IUnitOfWork, IDisposable
{
private CompetenceFunctionRepository _competencefunction;
private CompetenceAreaRepository _competencearea;
private CompetenceSpecificRepository _competencespecifc;
public UnitOfWork(ObjectContext context)
{
if (context == null)
{
throw new ArgumentNullException("Context was not supplied");
}
_context = context;
}
#region IUnitOfWork Members
public IRepository<CompetenceFunction> CompetenceFunctions
{
get
{
if (_competencefunction == null)
{
_competencefunction = new CompetenceFunctionRepository(_context);
}
return _competencefunction;
}
}
public IRepository<CompetenceArea> CompetenceAreas
{
get
{
if (_competencearea == null)
{
_competencearea = new CompetenceAreaRepository(_context);
}
return _competencearea;
}
}
public IRepository<CompetenceSpecific> CompetenceSpecifics
{
get
{
if (_competencespecifc == null)
{
_competencespecifc = new CompetenceSpecificRepository(_context);
}
return _competencespecifc;
}
}
--Im getting an error in this part of Repository
public Repository(ObjectContext context)
{
_objectSet = context.CreateObjectSet<T>();
}
There are no EntitySets defined for the specified entity type 'CompetencyManagement.Domain.Entities.CompetenceFunction'. If 'CompetencyManagement.Domain.Entities.CompetenceFunction' is a derived type, use the base type instead. Parameter name: TEntity
Here's how I implement in the controller
private IUnitOfWork _unitOfWork;
var a = _unitOfWork.CompetenceFunctions.GetAll();
return View(a);
You have to get derived type by the OfType function, e.g.
context.CreateObjectSet<Competence>().OfType<CompetenceFunction>()
In your case that would mean that there is only a CompetenceRepository that serves all derivatives of Competence.
Edit
(After your comment)
First, UoW is meant for temporarily storing changes that should be dealt with in one batch (like changes to be committed to the database). GetAll and similar functions are repository stuff.
But do you need repositories? I like this post. When beginning to know EF, I would focus on the ins and outs of EF without getting distracted too much by surrounding architecture. E.g. start with services that at the inside communicate directly with the context and expose methods like GetCompetenceFunctions, GetCompetenceAreas (using OfType), and SaveCompetenceFunction, ....
You can address these service methods directly from action methods in the MVC controllers.
I am fairly new to MVC, but after playing with it (MVC 3/Razor), I am hooked.
I have a few questions:
1) What is the best, or most widely used pattern to develop MVC apps in? Repository, DDD, UOW?
2) I am using the Entity Framework 4, so could some please explain to me or point me to a good source that will explain the Repository Pattern w/EF4? Doesn't EF4 take place as the business layer and the data access layer? Does the Repository Pattern even provide a benefit?
3) Also, one last question, could someone explain the whole relationship between the Controller, the Model and the View? I get the basics, but maybe a little more in depth of the correct way to use it. View Models - Say I have a view that displays customer info, and one that edits it, should I have a view model and an edit model, or can the be passed around?
4) Examples??
Thanks for the help up front,
$("Sam")
** EDIT **
Am I on the right track here:
Public Class HomeController
Inherits System.Web.Mvc.Controller
Function Index(ByVal id As Integer) As ActionResult
Return View(New HomeModel)
End Function
<HttpPost()> _
Function Index(ByVal Model As HomeModel) As ActionResult
Return View(Model)
End Function
End Class
Public Class HomeModel
Private _Repository As IRepository(Of Customer)
Public Property Customer As Customer
Public Sub New()
End Sub
Public Sub New(ByVal ID As Integer)
_Repository = New CustomerRepository
Customer = _Repository.GetByID(ID)
End Sub
End Class
Public Interface IRepository(Of T)
Function GetByID(ByVal ID As Integer) As T
Sub Add(ByVal Entity As T)
Sub Delete(ByVal Entity As T)
End Interface
Public Class CustomerRepository
Implements IRepository(Of Customer)
Public Sub Add(ByVal Entity As Customer) Implements IRepository(Of Customer).Add
End Sub
Public Sub Delete(ByVal Entity As Customer) Implements IRepository(Of Customer).Delete
End Sub
Public Function GetByID(ByVal ID As Integer) As Customer Implements IRepository(Of Customer).GetByID
Return New Customer With {.ID = ID, .FirstName = "Sam", .LastName = "Striano"}
End Function
End Class
Public Class Customer
Public Property ID As Integer
Public Property FirstName As String
Public Property LastName As String
End Class
I use generic repositories that get instantiated in a service class (using Dependency Injection with Ninject).
The service class essentially performs two functions:
It provides all the methods that the controller will consume.
It has a property called ViewModel, that essentially maps the data that the views need into a MyViewModel class.
The Controller consumes the service class. With this "pattern", your controllers look like:
namespace ES.eLearningFE.Areas.Courses.Controllers
{
public partial class CourseController : Controller
{
ICourseDisplayService service;
public CourseController(ICourseDisplayService service)
{
this.service = service;
}
public virtual ActionResult Display(int CourseId, int StepOrder, string PupilName, string TutorName)
{
service.CourseId = CourseId;
service.StepOrder = StepOrder;
service.PupilName = PupilName;
service.TutorName = TutorName;
if (Request.IsAjaxRequest())
{
return PartialView(service.ViewModel);
}
else
{
return View(service.ViewModel);
}
}
}
}
The ViewModel class only hold display data and no methods (except the odd really simple method to retrieve data from another property that is, for example a List<> object).
Works really well. An example of a service class:
namespace ES.eLearning.Domain.Services.Courses
{
public class SqlCourseDisplayService : ICourseDisplayService
{
DataContext db;
public SqlCourseDisplayService(DbDataContextFactory contextFactory)
{
db = contextFactory.Make();
CoursesRepository = new SqlRepository<Course>(db);
StepsRepository = new SqlRepository<CourseStep>(db);
StepLinksRepository = new SqlRepository<StepLink>(db);
UserCoursesRepository = new SqlRepository<UserCourse>(db);
CourseTutorsRepository = new SqlRepository<CourseTutor>(db);
UsersRepository = new SqlRepository<User>(db);
}
#region ICourseDisplayService Members
public ViewModels.CourseDisplayVM ViewModel
{
get
{
return new ViewModels.CourseDisplayVM
{
CourseId = this.CourseId,
CourseName = this.Course.Name,
Steps = this.Steps,
ActiveStepIndex = this.ActiveStepIndex,
CurrentStepIndex = this.CurrentStepIndex,
Pupil = new UserDto { UserId = this.PupilId, UserName = this.PupilName },
Tutors = this.GetTutors(this.CourseId),
Tutor = tutorName == null ? null : new UserDto { UserName = this.TutorName, UserId = this.TutorId}
};
}
}
#region Entities
int courseId;
public int CourseId
{
get
{
if (courseId == 0) throw new ApplicationException("Invalid Course Id!");
return courseId;
}
set
{
if (value == 0) throw new ApplicationException("Invalid Course Id!");
try
{
Course = (from c in CoursesRepository.Query where c.CourseId == value select c).First();
Steps = Course.CourseSteps.ToList();
courseId = value;
}
catch {throw new ApplicationException("No Course found for Course Id: " + value);}
}
}
public Data.Course Course { get; private set; }
public int StepOrder { get; set; }
public List<Data.CourseStep> Steps { get; private set; }
public int ActiveStepIndex
{
get
{
if (PupilName == null)
{
throw new ApplicationException("Pupil not set!");
}
if (CourseId == 0)
{
throw new ApplicationException("Course not set!");
}
try
{
var x = (from uc in UserCoursesRepository.Query where (uc.IdCourse == CourseId) && (uc.UserName == PupilName) select uc).First();
return x.ActiveStepIndex;
}
catch { throw new ApplicationException("Could not get Active Step!"); }
}
}
#endregion
#region Users
string tutorName;
public string TutorName
{
get
{
if (tutorName == null) throw new ApplicationException("Invalid call to get Tutor Name [Null Tutor Name]!");
return tutorName;
}
set
{
tutorName = value;
TutorId = (Guid)Membership.GetUser(tutorName).ProviderUserKey;
}
}
public Guid TutorId { get; set; }
string pupilName;
public string PupilName
{
get { return pupilName; }
set
{
pupilName = value;
PupilId = (Guid)Membership.GetUser(pupilName).ProviderUserKey;
}
}
public Guid PupilId { get; set; }
#endregion
#region Utility Properties
public int CurrentStepIndex { get; set; }
public int StepCount
{
get
{
return Steps == null ? 0 : Steps.Count();
}
}
#endregion
#region Private Utilities
private List<UserDto> GetTutors(int CourseId)
{
return (from ct in CourseTutorsRepository.Query join u in UsersRepository.Query
on ct.TutorName equals u.UserName
where (ct.CourseId == courseId)
select new UserDto { UserName = ct.TutorName, UserId = u.UserId }).ToList();
}
#endregion
#region Repositories
private IRepository<Course> CoursesRepository
{
get;
set;
}
private IRepository<CourseStep> StepsRepository
{
get;
set;
}
private IRepository<StepLink> StepLinksRepository
{
get;
set;
}
private IRepository<UserCourse> UserCoursesRepository
{
get;
set;
}
private IRepository<CourseTutor> CourseTutorsRepository
{
get;
set;
}
private IRepository<User> UsersRepository
{
get;
set;
}
#endregion
#endregion
}
}
May not be everyone's choice, but hey, it works for me... AND (more importantly) my clients and their users.
Edit
As requested in the comment below, the Repository that I use:
namespace ES.eLearning.Domain
{
public class SqlRepository<T> : IRepository<T> where T : class
{
DataContext db;
public SqlRepository(DataContext db)
{
this.db = db;
}
#region IRepository<T> Members
public IQueryable<T> Query
{
get { return db.GetTable<T>(); }
}
public List<T> FetchAll()
{
return Query.ToList();
}
public void Add(T entity)
{
db.GetTable<T>().InsertOnSubmit(entity);
}
public void Delete(T entity)
{
db.GetTable<T>().DeleteOnSubmit(entity);
}
public void Attach(T entity)
{
db.GetTable<T>().Attach(entity);
}
public void Save()
{
db.SubmitChanges();
}
#endregion
}
}
And the IRepository Interface:
namespace Wingspan.Web.Mvc
{
public interface IRepository<TEntity> where TEntity : class
{
List<TEntity> FetchAll();
IQueryable<TEntity> Query {get;}
void Add(TEntity entity);
void Delete(TEntity entity);
void Attach(TEntity entity);
void Save();
}
}
This should help you getting started. There are a lot of tutorials and videos available; for example:
Understanding Models, Views and Controllers
The ASP.NET MVC 2.0 basics and excellent introduction by Scott Hanselman. Personally one of my favorite speakers.
And also at www.asp.net; there are a few tutorials/examples to help you getting started. For example the Music Store sample
Unfortunately, I'm not so familiar with EF4/Repository pattern. But here's a blogpost about this pattern.
1) I would say that the repository pattern is the most widely used, then there is inversion of controll too.
2) I can't really point out the benefits with using a repository for entity framework other than that the controller should not know about how to acces data other then asking a repository. This makes it easy to switch it out sometime.
You can also eager load the data to make sure that the view don't call the database in every iteration of a foreach, for example a collection of users to display data from a child entity. You can probly do this anyway, but I feel that the repository is the right place to do it.
3) I can't tell you about the concept in a more in depth way, but I can tell some about viewmodels. In my opinion you should only use viewmodels if there is anything more then one entity you want to send to the view, for example a list of countries. You can alo use a viewmodel to "flatten" out very complex objects.
I would defiantly say the repository pattern is used a lot. This pattern can be used with Dependency Injection. Using Dependency Injection makes Unit Testing a breeze because you can snap different repositories to an abstract repoistory. Check out http://ninject.org/ for a simple to use Dependecy injector for .NET.
View Models should hold display data and transfer that data from the controller to the view. If you want to edit and display customer info, take a look at this
I have a custom List (MyCustomList) that implements List(Of MyCustomClass).
I want to run a LINQ query against that and return a filtered MyCustomList.
Public ReadOnly Property DebitTransactions As MyCustomList
Get
Return From item In Me Where item.IsDebit = True Select item
End Get
End Property
I get a type conversion here because the LinQ query doesn't return the list in the same MyCustomList that it was filtering. It cannot convert a WhereSelectListIterator object (which is returned) to a MyCustomClass.
I really need the filtered results to be in the same format they came in as. Any suggestions?
If you implement your own Where exthension method you can keep using linq syntax.
public class MyCustomList : List<MyCustomClass>
{
public MyCustomList() : base()
{
}
public MyCustomList(IEnumerable<MyCustomClass> coll) : base(coll)
{
}
}
public static class MyCustomListExtensions
{
public static MyCustomList Where(this MyCustomList myList, Func<MyCustomClass, bool> predicate)
{
return new MyCustomList(Enumerable.Where(myList, predicate));
}
}
public class MyCustomClass
{
public int Int1 { get; set; }
public string Str1 { get; set; }
}
And here I'm using the custom Where implementation:
var myList = new MyCustomList()
{
new MyCustomClass() { Int1 = 1},
new MyCustomClass() { Int1 = 2},
new MyCustomClass() { Int1 = 3},
};
MyCustomList filteredList = from item in myList where item.Int1 > 1 select item;
Assert.AreEqual(2, filteredList.Count);
You have to iterate the list, add them to a collection, and return the collection. Linq doesn't support, directly, conversion of iterators to custom return types other than List, arrays and Dictionaries.
Not sure if what I am trying is possible or not, but I'd like to reuse a linq expression on an objects parent property.
With the given classes:
class Parent {
int Id { get; set; }
IList<Child> Children { get; set; }
string Name { get; set; }
}
class Child{
int Id { get; set; }
Parent Dad { get; set; }
string Name { get; set; }
}
If i then have a helper
Expression<Func<Parent,bool> ParentQuery() {
Expression<Func<Parent,bool> q = p => p.Name=="foo";
}
I then want to use this when querying data out for a child, along the lines of:
using(var context=new Entities.Context) {
var data=context.Child.Where(c => c.Name=="bar"
&& c.Dad.Where(ParentQuery));
}
I know I can do that on child collections:
using(var context=new Entities.Context) {
var data=context.Parent.Where(p => p.Name=="foo"
&& p.Childen.Where(childQuery));
}
but cant see any way to do this on a property that isnt a collection.
This is just a simplified example, actually the ParentQuery will be more complex and I want to avoid having this repeated in multiple places as rather than just having 2 layers I'll have closer to 5 or 6, but all of them will need to reference the parent query to ensure security.
If this isnt possible, my other thought was to somehow translate the ParentQuery expression to be of the given type so effectively:
p => p.Name=="foo";
turns into:
c => c.Dad.Name=="foo";
but using generics / some other form of query builder that allows this to retain the parent query and then just have to build a translator per child object that substitutes in the property route to the parent.
EDIT:
Following on from comments by #David morton
Initially that looks like I can just change from Expression to a delegate function and then call
.Where(ParentQuery()(c.Dad));
However I am using this in a wider repository pattern and cant see how I can use this with generics and predicate builders - I dont want to retrieve rows from the store and filter on the client (web server in this case). I have a generic get data method that takes in a base expression query. I then want to test to see if the supplied type implements ISecuredEntity and if it does append the securityQuery for the entity we are dealing with.
public static IList<T> GetData<T >(Expression<Func<T, bool>> query) {
IList<T> data=null;
var secQuery=RepositoryHelperers.GetScurityQuery<T>();
if(secQuery!=null) {
query.And(secQuery);
}
using(var context=new Entities.Context()) {
var d=context.GetGenericEntitySet<T>();
data=d.ToList();
}
return data;
}
ISecuredEntity:
public interface ISecuredEntity : IEntityBase {
Expression<Func<T, bool>> SecurityQuery<T>();
}
Example Entity:
public partial class ExampleEntity: ISecuredEntity {
public Expression<Func<T, bool>> SecurityQuery<T>() {
//get specific type expression and make generic
Type genType = typeof(Func<,>).MakeGenericType(typeof(ExampleEntity), typeof(bool));
var q = this.SecurityQuery(user);
return (Expression<Func<T, bool>>)Expression.Lambda(genType, q.Body, q.Parameters);
}
public Expression<Func<ExampleEntity, bool>> SecurityQuery() {
return e => e.OwnerId==currentUser.Id;
}
}
and repositoryHelpers:
internal static partial class RepositoryHelpers {
internal static Expression<Func<T, bool>> SecureQuery<T>() where T : new() {
var instanceOfT = new T();
if (typeof(Entities.ISecuredEntity).IsAssignableFrom(typeof(T))) {
return ((Entities.ISecuredEntity)instanceOfT).SecurityQuery<T>();
}
return null;
}
}
EDIT Here is the (eventual) solution
I ended up going back to using expressions, and using LinqKit Invoke. Note: for EF I also had to call .AsExpandable() on the entitySet
The key part is being able to call:
Product.SecureFunction(user).Invoke(pd.ParentProduct);
so that I can pass in the context into my parent query
My end classes look like:
public interface ISecureEntity {
Func<T,bool> SecureFunction<T>(UserAccount user);
}
public class Product : ISecureEntity {
public Expression<Func<T,bool>> SecureFunction<T>(UserAccount user) {
return SecureFunction(user) as Expression<Func<T,bool>>;
}
public static Expression<Func<Product,bool>> SecureFunction(UserAccount user) {
return f => f.OwnerId==user.AccountId;
}
public string Name { get;set; }
public string OwnerId { get;set; }
}
public class ProductDetail : ISecureEntity {
public Expression<Func<T,bool>> SecureFunction<T>(UserAccount user) {
return SecureFunction(user) as Expression<Func<T,bool>>;
}
public static Func<ProductDetail,bool> SecureFunction(UserAccount user) {
return pd => Product.SecureFunction(user).Invoke(pd.ParentProduct);
}
public int DetailId { get;set; }
public string DetailText { get;set; }
public Product ParentProduct { get;set; }
}
Usage:
public IList<T> GetData<T>() {
IList<T> data=null;
Expression<Func<T,bool>> query=GetSecurityQuery<T>();
using(var context=new Context()) {
var d=context.GetGenericEntitySet<T>().Where(query);
data=d.ToList();
}
return data;
}
private Expression<Func<T,bool>> GetSecurityQuery<T>() where T : new() {
var instanceOfT = new T();
if (typeof(Entities.ISecuredEntity).IsAssignableFrom(typeof(T))) {
return ((Entities.ISecuredEntity)instanceOfT).SecurityQuery<T>(GetCurrentUser());
}
return a => true; //returning a dummy query
}
}
Thanks for the help all.
You're overthinking it.
First, don't return an Expression<Func<Parent, bool>>, that'll require you to compile the expression. Return simply a Func<Parent, bool> instead.
Next, it's all in how you call it:
context.Children.Where(c => c.Name == "bar" && ParentQuery()(c.Dad));
context.Parents.Where(ParentQuery());