How to sort upon unknown dynamic generic List?

Question

Upadate:

I have prepared a generic function for capturing database rows for generation the listing. My method is exactly like this.

    public class GenericDataAccess<TEntity> : IGenericRepository<TEntity> where TEntity : class
    {
        internal ELearningDBContext ELearningDBContext;
        internal DbSet<TEntity> ELearningDBSet;

        public GenericDataAccess(ELearningDBContext context)
        {
            this.ELearningDBContext = context;
            this.ELearningDBSet = context.Set<TEntity>();
        }
        public virtual PagingModel<TEntity> GetAllPaged(int pagesize, NameValueCollection queryString)
        {
            return ELearningDBSet.AsQueryable().ToList();
        }
     }

Here I am facing a problem to sort this list. Because the TEntity is changing time to time. However, I have a common field in every Entity named Id. So I want to sort each and every model by Id in descending order.

I have tried this way. But it was not effective, moreover, it's generating an exception.

ELearningDBSet.AsQueryable()..OrderByDescending(i=>typeof(TEntity).GetProperty("Id")).ToList();

I have gone through these questions Q1, Q2, Q3, Q4. However, these were not effective. I prefer C# code. Any kind of perfect solution is highly appreciated. Thank you.

it's the table context. For example `internal DbSet ELearningDBSet;` — Ananda G, Sep 13 '17 at 05:42
Could you please see that, if it's not enough then please ask. — Ananda G, Sep 13 '17 at 05:48
Please see my question in the previous comment. Also what exception do you get? — Gilad Green, Sep 13 '17 at 05:55
`Do all the Entitys derive from the same Entity class?` => No. `Also what exception do you get?` => I just want to sort them `descending` order by `Id`. — Ananda G, Sep 13 '17 at 07:18

aaronR · Answer 1 · 2017-09-14T13:05:39.320

Create an interface for all of your data entities to implement

public interface IEntityBase
{
    long Id { get; set; }
}

Then in your data class, in your case TEntity, Implement the IEntityBase interface.

public partial class MyTEntity: IEntityBase
{
    public long Id { get; set; }

    //Other attributes as needed.
}

In your generic class GenericDataAccess<TEntity> add a constraint to make TEntity implement the new interface IEntityBase. Then in the GetAllPaged method add the OrderByDescending() method call using the IEntityBase.Id property.

public class GenericDataAccess<TEntity> : IGenericRepository<TEntity> where TEntity : class, IEntityBase
    {
        internal ELearningDBContext ELearningDBContext;
        internal DbSet<TEntity> ELearningDBSet;

        public GenericDataAccess(ELearningDBContext context)
        {
            this.ELearningDBContext = context;
            this.ELearningDBSet = context.Set<TEntity>();
        }
        public virtual PagingModel<TEntity> GetAllPaged(int pagesize, NameValueCollection queryString)
        {
            return ELearningDBSet.AsQueryable().OrderByDescending(o => o.Id).ToList();
        }
     }

UPDATED: Added the partial descriptor for the MyEntityclass.

@Mafii are you referring to the `MyEntity` class specifically? — aaronR, Sep 14 '17 at 13:03
Yes. Create a new file, make the class partial, and add the interface (and if required the implementation with an alias). When using EF6, the entity itself should be partial by default — Mafii, Sep 14 '17 at 13:05

Ananda G · Accepted Answer · 2017-09-14T12:59:12.597

2

Wow!! I have just got a wonderful solution. I have just used it.

 ELearningDBSet.AsQueryable().SortBy("Id" + " Desc").ToList();

Here the SortBy() function I used, got it from the .Net Library named System.Web.UI.WebControls.QueryExtensions. For more details see here. Really it was a wonderful and outstanding solution for me.

edited Sep 14 '17 at 12:59

answered Sep 13 '17 at 11:16

Ananda G

2,389
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This is not user defined function. I have got the function from `System.Web.UI.WebControls.QueryExtensions` – Ananda G Sep 14 '17 at 11:13
I got it and i'm doing that. Thanks for your support. – Ananda G Sep 14 '17 at 12:59
Using a presentation layer library to a repository class is at best a "hack", secondly you open yourself up to run time issues since you could encounter a `TEntity` object that doesn't have the required `Id` property. – aaronR Sep 15 '17 at 14:25

score 1 · Answer 3 · answered Sep 13 '17 at 06:19

You can build an Expression tree yourself e.g.

public static IQueryable<T> Sort<T>(this IQueryable<T> source, string field)
{
    var p = Expression.Parameter(typeof(T));
    var exp = Expression.Property(p, field);
    return source.OrderBy(Expression.Lambda<Func<T, object>>(exp, p));
}

How to sort upon unknown dynamic generic List?

3 Answers3