Question

我几乎搜索了我能找到的每个问题，博客或文档，以帮助我回答这个问题的答案。一些实际上帮助我更接近它，但我仍然没有解决它，因为大多数要么已经过时，要么没有真正与我需要的点。不要打扰告诉我关于表达式的事情，因为如果我采取更长的路线，我就不会使用这个库。

我的项目目标是通过使用泛型方法，仅使用表/列名称字符串和用于过滤的值来提供过滤和排序。长话短说，我有两个表，关系为1到n，基本上这样连接，我想按客户的名字订购：

public partial class Transactions{
    public ICollection<Customer> customer { get; set; };
}

public partial class Customer{
    public string name { get; set; };
}

到目前为止，我几乎需要实现我想要的，除了弄清楚如何正确构造OrderBy字符串，以一种我使用单个ICollection结果的方式。

到目前为止我的内容非常类似（对于我的文档过于冗长而感到抱歉）：

using System.Linq.Dynamic;
using System.Reflection;

namespace com.betha.common
{
    public class Filter
    {
        /// <summary>
        /// Dictionary of codenames and column names populated by a different, specific class (properties.Add("customer", "tb_customer.name"))
        /// </summary>
        public Dictionary<string, string> properties;

        public Filter(Dictionary<string, string> properties)
        {
            this.properties = properties;
        }

        /// <summary>
        /// Generic method designed to filter and order using just lists of column names and values
        /// </summary>
        /// <typeparam name="T">Type of the first IQueryable</typeparam>
        /// <typeparam name="T2">Type of the second IQueryable</typeparam>
        /// <param name="query">IQueryable containing the results from the parent table (context.table1).AsQueryable();</param>
        /// <param name="query2">IQueryable containing a single result from a descendant table (context.table2.Select(t2 => t2.field).FirstOrDefault()).AsQueryable();</param>
        /// <param name="prop">Property codename that if used, matches a properties codename Key</param>
        /// <param name="descend">Condition for ascending or descending results</param>
        /// <returns>Ordered and/or filtered IQueryable</returns>
        public IQueryable<T> FilterandOrder<T, T2>(IQueryable<T> query, IQueryable<T2> query2, string prop = null, string descend = null)
        {
            if (!String.IsNullOrEmpty(prop))
            {
                foreach (KeyValuePair<string, string> item in properties)
                {
                    if (prop == item.Key)
                    {
                        prop = item.Value;
                    }
                }
                T2 subprop = query2.FirstOrDefault();

                if (prop.Contains("."))
                {
                    switch (prop.Split('.'))
                    {
                        default:
                            PropertyInfo property = subprop.GetType().GetProperty(prop.Split('.')[1]);
                            ParameterInfo[] index = property.GetIndexParameters();
                            object value = subprop.GetType().GetProperty(prop.Split('.')[1]).GetValue(subprop, index);

                            //This is the main issue, I have pretty much everything I should need, but I can't imagine how to write this OrderBy string properly.
                            //If I were to do it without the library: table.OrderBy(t => t.table2.Select(t2 => t2.field).FirstOrDefault());
                            //Without ordering by an ICollection property, like in the else below, string should look like: "field".
                            //Or in case of a 1 to 1 relationship, "table2.field".
                            query = DynamicQueryable.OrderBy(query, prop + (descend == "dec" ? " descending" : ""), value);
                            break;
                    }
                }
                else
                {
                    query = DynamicQueryable.OrderBy(query, prop + (descend == "dec" ? " descending" : ""));
                }
            }

            return query;
        }
    }
}

Answer 1

您可以使用支持的功能t => t.table2.Select(t2 => t2.field).FirstOrDefault()替换Min()：

OrderBy("table2.Min(field)");

通过ICollection属性进行排序，使用其名称作为Dynamic Linq Library的字符串

1 个答案: