Dynamic Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> Expression

问题

I am using patterns mentioned here http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application

And i am using method below to query EF

public virtual IEnumerable<TEntity> Get(
        Expression<Func<TEntity, bool>> filter = null,
        Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
        string includeProperties = "")
    {
        IQueryable<TEntity> query = dbSet;

        if (filter != null)
        {
            query = query.Where(filter);
        }

        foreach (var includeProperty in includeProperties.Split
            (new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries))
        {
            query = query.Include(includeProperty);
        }

        if (orderBy != null)
        {
            return orderBy(query).ToList();
        }
        else
        {
            return query.ToList();
        }
    }

Now i want to create dynamic Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> expression to order my data.

I know only field name as string and order type (ascending, descending) as string (asc, desc)

回答1:

finally i could write the method i want.

 public static Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> GetOrderBy(string orderColumn, string orderType) {
            Type typeQueryable = typeof(IQueryable<TEntity>);
            ParameterExpression argQueryable = Expression.Parameter(typeQueryable, "p");
            var outerExpression = Expression.Lambda(argQueryable, argQueryable);
            string[] props = orderColumn.Split('.');
            IQueryable<TEntity> query = new List<TEntity>().AsQueryable<TEntity>();
            Type type = typeof(TEntity);
            ParameterExpression arg = Expression.Parameter(type, "x");

            Expression expr = arg;
            foreach(string prop in props) {
                PropertyInfo pi = type.GetProperty(prop, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);
                expr = Expression.Property(expr, pi);
                type = pi.PropertyType;
            }
            LambdaExpression lambda = Expression.Lambda(expr, arg);
            string methodName = orderType == "asc" ? "OrderBy" : "OrderByDescending";

            MethodCallExpression resultExp =
                Expression.Call(typeof(Queryable), methodName, new Type[] { typeof(TEntity), type }, outerExpression.Body, Expression.Quote(lambda));
            var finalLambda = Expression.Lambda(resultExp, argQueryable);
            return (Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>>)finalLambda.Compile();
        }

This method takes two parameters, first one field name other one is asc or desc. Result of method can be used directly with IQueryable object.

Thanks for your helps

回答2:

This is very late to the party but the correct answer is located on another question at https://stackoverflow.com/a/10935223/14275

var students = repository.Get(x => x.FirstName = "Bob",q => q.OrderBy(s => s.LastName));

回答3:

I am not sure what exactly you want to accomplish, but I had changed your code and add some example to demonstrate how does it work.

This is a simple console app, which has dummyText as list. Queryable method enables to use filter and sort expression as you want. I hope it helps

 class Program
{

    private List<string> _dummyText = new List<string>(){ "Arda",
        "Araba",
        "Antartika",
        "Balon"};

    static void Main(string[] args)
    {
        Program p = new Program();
        List<string> result = p.Get(s => s.StartsWith("A"), orderBy: q => q.OrderBy(d => d.Length)).ToList();

        Console.ReadLine();
    }


    public virtual IEnumerable<string> Get(
    Expression<Func<string, bool>> filter = null,
    Func<IQueryable<string>, IOrderedQueryable<string>> orderBy = null)
    {

        IQueryable<string> query = _dummyText.AsQueryable();

        if (filter != null)
        {
            query = query.Where(filter);
        }

        if (orderBy != null)
        {
            return orderBy(query).ToList();
        }
        else
        {
            return query.ToList();
        }



    }

}

来源：https://stackoverflow.com/questions/16009694/dynamic-funciqueryabletentity-iorderedqueryabletentity-expression