Question

我正在使用这里提到的模式 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

我正在使用下面的方法来查询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();
        }
    }

现在我想创建动态Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>>表达式来订购我的数据。

我只知道字段名称为字符串，顺序类型（升序，降序）为字符串（asc，desc）

Answer 1

最后我可以写出我想要的方法。

 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();
        }

此方法有两个参数，第一个是字段名，另一个是asc或desc。方法的结果可以直接用于IQueryable对象。

感谢您的帮助

Answer 2

我不确定您想要完成的是什么，但我已经更改了您的代码并添加了一些示例来演示它是如何工作的。

这是一个简单的控制台应用程序，其中包含dummyText作为列表。可查询方法允许您根据需要使用过滤器和排序表达式。我希望它有所帮助

 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();
        }



    }

}

Answer 3

这对派对来说已经很晚了，但正确的答案位于https://stackoverflow.com/a/10935223/14275

的另一个问题上

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

Dynamic Func <iqueryable <tentity>，IOrderedQueryable <tentity>＆gt;表达</tentity> </IQueryable的<tentity>

3 个答案: