1 /// 

  2 /// 实现动态排序
  3 /// 来源博客园的一个大神，具体实现原理是利用实体和排序字段自动生成一个表达式
  4 /// 再利用IQuerable的方法实现
  5 /// 有一部分比较像微软的源码 ZhangQC 2016.10.20
  6 /// 
  7 public static class DynamicOrder
  8 {
  9 #region Private 表达式树
 10 /// 

 11 /// 构建表达式树 结果类似于 j=>j.Name
 12 /// ZhangQc 2016.10.20
 13 /// 
 14 /// 
 15 /// 
 16 /// 
 17 private static LambdaExpression GenerateSelector(String propertyName, out Type resultType) where TEntity : class
 18 {
 19 PropertyInfo property;
 20 Expression propertyAccess;
 21 var parameter = Expression.Parameter(typeof(TEntity), "j");
 22 
 23 if (propertyName.Contains('.'))
 24 {
 25 String[] childProperties = propertyName.Split('.');
 26 property = typeof(TEntity).GetProperty(childProperties[0]);
 27 propertyAccess = Expression.MakeMemberAccess(parameter, property);
 28 for (int i = 1; i < childProperties.Length; i++)
 29 {
 30 property = property.PropertyType.GetProperty(childProperties[i]);
 31 propertyAccess = Expression.MakeMemberAccess(propertyAccess, property);
 32 }
 33 }
 34 else
 35 {
 36 property = typeof(TEntity).GetProperty(propertyName);
 37 propertyAccess = Expression.MakeMemberAccess(parameter, property);
 38 }
 39 
 40 resultType = property.PropertyType;
 41 
 42 return Expression.Lambda(propertyAccess, parameter);
 43 }
 44 
 45 /// 

 46 /// 生成方法调用
 47 /// 
 48 /// 
 49 /// 
 50 /// 
 51 /// 
 52 /// 
 53 private static MethodCallExpression GenerateMethodCall(IQueryable source, string methodName, String fieldName) where TEntity : class
 54 {
 55 Type type = typeof(TEntity);
 56 Type selectorResultType;
 57 LambdaExpression selector = GenerateSelector(fieldName, out selectorResultType);
 58 MethodCallExpression resultExp = Expression.Call(typeof(Queryable), methodName,
 59 new Type[] { type, selectorResultType },
 60 source.Expression, Expression.Quote(selector));
 61 return resultExp;
 62 }
 63 #endregion
 64 
 65 public static IOrderedQueryable OrderBy(this IQueryable source, string fieldName) where TEntity : class
 66 {
 67 MethodCallExpression resultExp = GenerateMethodCall(source, "OrderBy", fieldName);
 68 return source.Provider.CreateQuery(resultExp) as IOrderedQueryable;
 69 }
 70 
 71 public static IOrderedQueryable OrderByDescending(this IQueryable source, string fieldName) where TEntity : class
 72 {
 73 MethodCallExpression resultExp = GenerateMethodCall(source, "OrderByDescending", fieldName);
 74 return source.Provider.CreateQuery(resultExp) as IOrderedQueryable;
 75 }
 76 
 77 public static IOrderedQueryable ThenBy(this IOrderedQueryable source, string fieldName) where TEntity : class
 78 {
 79 MethodCallExpression resultExp = GenerateMethodCall(source, "ThenBy", fieldName);
 80 return source.Provider.CreateQuery(resultExp) as IOrderedQueryable;
 81 }
 82 
 83 public static IOrderedQueryable ThenByDescending(this IOrderedQueryable source, string fieldName) where TEntity : class
 84 {
 85 MethodCallExpression resultExp = GenerateMethodCall(source, "ThenByDescending", fieldName);
 86 return source.Provider.CreateQuery(resultExp) as IOrderedQueryable;
 87 }
 88 public static IOrderedQueryable OrderUsingSortExpression(this IQueryable source, string sortExpression) where TEntity : class
 89 {
 90 String[] orderFields = sortExpression.Split(',');
 91 IOrderedQueryable result = null;
 92 for (int currentFieldIndex = 0; currentFieldIndex < orderFields.Length; currentFieldIndex++)
 93 {
 94 String[] expressionPart = orderFields[currentFieldIndex].Trim().Split(' ');
 95 String sortField = expressionPart[0];
 96 Boolean sortDescending = (expressionPart.Length == 2) && (expressionPart[1].Equals("DESC", StringComparison.OrdinalIgnoreCase));
 97 if (sortDescending)
 98 {
 99 result = currentFieldIndex == 0 ? source.OrderByDescending(sortField) : result.ThenByDescending(sortField);
100 }
101 else
102 {
103 result = currentFieldIndex == 0 ? source.OrderBy(sortField) : result.ThenBy(sortField);
104 }
105 }
106 return result;
107 }
108 
109 
110 //使用方法
111 // var query = (from d in ((VinnoTech.Gaia2.DB.g2_dsource[])result)
112 // join p in WebApiApplication.entities.g2_propnames
113 // on d.dsource_item equals p.prop_name
114 // orderby sidx
115 // select new
116 // {
117 // d.dsource_id,
118 // d.dsource_name,
119 // dsource_item = p.prop_description,
120 // d.dsource_description,
121 // dsource_status = d.dsource_status == "1" ? "启用" : "禁用",
122 // d.dsource_expiredday,
123 // dsource_alarmhigh = (d.dsource_alarmhigh == -65535 || d.dsource_alarmhigh == 65535) ? "未禁用" : d.dsource_alarmhigh.ToString(),
124 // dsource_alarmlow = (d.dsource_alarmlow == -65535 || d.dsource_alarmhigh == 65535) ? "未禁用" : d.dsource_alarmhigh.ToString(),
125 // dsource_alarmdeltadata = (d.dsource_alarmdeltadata == -65535 || d.dsource_alarmhigh == 65535) ? "未禁用" : d.dsource_alarmhigh.ToString(),
126 // dsource_alarmidle = (d.dsource_alarmidle == -65535 || d.dsource_alarmhigh == 65535) ? "未禁用" : d.dsource_alarmhigh.ToString(),
127 // d.dsource_formula,
128 // dsource_updatetime = d.dsource_updatetime.ToString("yyyy-MM-dd HH:mm:ss")
129 // }).AsQueryable();
130 
131 //page = page <= query.Count() / rows + 1 ? page : 1;
132 
133 //query = query.OrderUsingSortExpression("dsource_name asc,dsource_item desc").Skip(rows * (page - 1)).Take(rows);
134 }