OrderByWithString

LinqExtensions.cs

using System;
using System.Linq;
using System.Linq.Expressions;

namespace Net.Elendia.Sample.Linq;

public static class LinqExtensions {

    /// <summary>
    /// ORDER BY 句文字列を使ってソートします。
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="source"></param>
    /// <param name="orderByQuery">ORDER BY 句文字列</param>
    /// <returns></returns>
    /// <exception cref="ArgumentException"></exception>
    /// <remarks>
    /// <code>Hoge,Fuga DESC,Piyo,Puyo DESC</code>
    /// のような文字列を受け取り、
    /// <code>OrderBy(x => x.Hoge).ThenByDescending(x => x.Fuga).ThenBy(x => x.Piyo).ThenByDescending(x => x.Puyo)</code>
    /// のようなメソッド呼び出しに変換します。
    /// </remarks>
    public static IQueryable<T> OrderByWithString<T>(this IQueryable<T> source, string orderByQuery) {
        IQueryable<T> result = source;

        // ORDER BY 句文字列を列ごとに分解
        var orderByList = orderByQuery.Split(',')
                                      .Select(a => {
                                          string[] pair = a.Trim().Split(' ');
                                          string name = pair[0];
                                          bool isAsc = (pair.Length == 1) || (pair[1] != "DESC");
                                          return new { Name = name, IsAsc = isAsc };
                                      })
                                      .ToList();

        if (orderByList.Count == 0) {
            throw new ArgumentException("無効な ORDER BY 句が指定されました。");
        }

        var type = typeof(T);

        var parameter = Expression.Parameter(type, "x");

        for (int i = 0; i < orderByList.Count; i++) {
            // メソッド名を決定
            string methodName = ((i == 0), orderByList[i].IsAsc) switch {
                (true, true) => "OrderBy",
                (true, false) => "OrderByDescending",
                (false, true) => "ThenBy",
                (false, false) => "ThenByDescending",
            };

            // ラムダ式を構築
            var propertyInfo = type.GetProperty(orderByList[i].Name)
                            ?? throw new ArgumentException("無効な ORDER BY 句が指定されました。");
            var propertyAccess = Expression.MakeMemberAccess(parameter, propertyInfo);
            var orderByExpression = Expression.Lambda(propertyAccess, parameter);
            var resultExpression = Expression.Call(
                typeof(Queryable),
                methodName,
                new[] { type, propertyInfo.PropertyType },
                result.Expression,
                Expression.Quote(orderByExpression)
            );

            // 連結
            result = result.Provider.CreateQuery<T>(resultExpression);
        }

        return result;
    }
}