表达式树的说明与运用
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说明: 在我们日常代码开发中很多的地方都用到了Lambda表达式进行过滤操作，我们很多优秀的ORM也是使用表达式来进行数据的查询。但是对于一些复杂的过 滤单纯的使用Lambda已经不能够解决问题了那么就需要表达式树来进行条件的一个拼接。
下面介绍一个本人写的一个工具类有助于项目中更好的使用:
1 public static class ExpressionTreeTools 2 3 /// <summary> 4 /// 相当于&&操作 5 /// ——just0ne 6 /// </summary> 7 /// <param name="thisFilter">已生成的过滤条件</param> 8 /// <param name="otherFilter">未生成的过滤条件</param> 9 /// <returns>新的过滤</returns> 10 public static Expression And(this Expression thisFilter, Expression otherFilter) 11 12 return Expression.AndAlso(thisFilter, otherFilter); 13 14 /// <summary> 15 /// 相当于||操作 16 /// ——just0ne 17 /// </summary> 18 /// <param name="thisFilter">已生成的过滤条件</param> 19 /// <param name="otherFilter">未生成的过滤条件</param> 20 /// <returns>新的过滤</returns> 21 public static Expression Or(this Expression thisFilter, Expression otherFilter) 22 23 return Expression.OrElse(thisFilter, otherFilter); 24 25 /// <summary> 26 /// 相当于==操作 27 /// ——just0ne 28 /// </summary> 29 /// <param name="thisParameterExpression">查询对象</param> 30 /// <param name="propertieName">属性名称</param> 31 /// <param name="propertieValue">属性值</param> 32 /// <returns>新的过滤</returns> 33 public static Expression GotoEqual(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 34 35 return Expression.Equal(Expression.Property(thisParameterExpression, propertieName), Expression.Constant(propertieValue)); 36 37 /// <summary> 38 /// 相当于>=操作 39 /// ——just0ne 40 /// </summary> 41 /// <param name="thisParameterExpression">查询对象</param> 42 /// <param name="propertieName">属性名称</param> 43 /// <param name="propertieValue">属性值</param> 44 /// <returns>新的过滤</returns> 45 public static Expression GotoGreaterThanOrEqual<T>(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 46 47 //大于或等于 48 return Expression.GreaterThanOrEqual(Expression.Property(thisParameterExpression, propertieName), Expression.Constant(propertieValue, typeof(T))); 49 50 /// <summary> 51 /// 相当于小于等于操作 52 /// ——just0ne 53 /// </summary> 54 /// <param name="thisParameterExpression">查询对象</param> 55 /// <param name="propertieName">属性名称</param> 56 /// <param name="propertieValue">属性值</param> 57 /// <returns>新的过滤</returns> 58 public static Expression GotoLessThanOrEqual<T>(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 59 60 //小于或等于 61 return Expression.LessThanOrEqual(Expression.Property(thisParameterExpression, propertieName), Expression.Constant(propertieValue, typeof(T))); 62 63 /// <summary> 64 /// 相当于>操作 65 /// ——just0ne 66 /// </summary> 67 /// <param name="thisParameterExpression">查询对象</param> 68 /// <param name="propertieName">属性名称</param> 69 /// <param name="propertieValue">属性值</param> 70 /// <returns>新的过滤</returns> 71 public static Expression GotoGreaterThan<T>(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 72 73 //大于 74 return Expression.GreaterThan(Expression.Property(thisParameterExpression, propertieName), Expression.Constant(propertieValue, typeof(T))); 75 76 /// <summary> 77 /// 相当于小于操作 78 /// ——just0ne 79 /// </summary> 80 /// <param name="thisParameterExpression">查询对象</param> 81 /// <param name="propertieName">属性名称</param> 82 /// <param name="propertieValue">属性值</param> 83 /// <returns>新的过滤</returns> 84 public static Expression GotoLessThan<T>(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 85 86 //小于 87 return Expression.LessThan(Expression.Property(thisParameterExpression, propertieName), Expression.Constant(propertieValue, typeof(T))); 88 89 /// <summary> 90 /// 相当于>=操作 91 /// ——just0ne 92 /// </summary> 93 /// <param name="thisParameterExpression">查询对象</param> 94 /// <param name="propertieName">属性名称</param> 95 /// <param name="propertieValue">属性值</param> 96 /// <returns>新的过滤</returns> 97 public static Expression GotoGreaterThanOrEqualByDateTime(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 98 99 //大于或等于 100 return Expression.GreaterThanOrEqual(Expression.Property(thisParameterExpression, propertieName), Expression.Constant(propertieValue, typeof(DateTime?))); 101 102 /// <summary> 103 /// 相当于小于或等于操作 104 /// ——just0ne 105 /// </summary> 106 /// <param name="thisParameterExpression">查询对象</param> 107 /// <param name="propertieName">属性名称</param> 108 /// <param name="propertieValue">属性值</param> 109 /// <returns>新的过滤</returns> 110 public static Expression GotoLessThanOrEqualByDateTime(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 111 112 //小于或等于 113 return Expression.LessThanOrEqual(Expression.Property(thisParameterExpression, propertieName), Expression.Constant(propertieValue, typeof(DateTime?))); 114 115 /// <summary> 116 /// 相当于>操作 117 /// ——just0ne 118 /// </summary> 119 /// <param name="thisParameterExpression">查询对象</param> 120 /// <param name="propertieName">属性名称</param> 121 /// <param name="propertieValue">属性值</param> 122 /// <returns>新的过滤</returns> 123 public static Expression GotoGreaterThanByDateTime(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 124 125 //大于 126 return Expression.GreaterThan(Expression.Property(thisParameterExpression, propertieName), Expression.Constant(propertieValue, typeof(DateTime?))); 127 128 /// <summary> 129 /// 相当于小于操作 130 /// —一just0ne 131 /// </summary> 132 /// <param name="thisParameterExpression">查询对象</param> 133 /// <param name="propertieName">属性名称</param> 134 /// <param name="propertieValue">属性值</param> 135 /// <returns>新的过滤</returns> 136 public static Expression GotoLessThanByDateTime(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 137 138 //小于 139 return Expression.LessThan(Expression.Property(thisParameterExpression, propertieName), Expression.Constant(propertieValue, typeof(DateTime?))); 140 141 142 /// <summary> 143 /// 一一just0ne 144 /// 包含操作 相当余 a=> arr.Contains(a.ID) 145 /// 如果arr中数据量过大则不适用linq 146 /// </summary> 147 /// <param name="thisParameterExpression">查询对象</param> 148 /// <param name="propertieName">属性名称</param> 149 /// <param name="propertieValue">属性值</param> 150 /// <returns>新的过滤</returns> 151 public static Expression ContainsOperations(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 152 153 MethodInfo method = null; 154 MemberExpression member = Expression.Property(thisParameterExpression, propertieName); 155 var containsMethods = typeof(Enumerable).GetMethods(BindingFlags.Static | BindingFlags.Public).Where(m => m.Name == "Contains"); 156 foreach (var m in containsMethods) 157 158 if (m.GetParameters().Count() == 2) 159 160 method = m; 161 break; 162 163 164 method = method.MakeGenericMethod(member.Type); 165 var exprContains = Expression.Call(method, new Expression[] Expression.Constant(propertieValue), member ); 166 return exprContains; 167 168 169 /// <summary> 170 /// 一一just0ne 171 /// 包含操作 相当于 a=>a.ID.Contains(key) 172 /// </summary> 173 /// <param name="thisParameterExpression">查询对象</param> 174 /// <param name="propertieName">属性名称</param> 175 /// <param name="propertieValue">属性值</param> 176 /// <returns>新的过滤</returns> 177 public static Expression Contains(this ParameterExpression thisParameterExpression, string propertieName, object propertieValue) 178 179 var propertyExp = Expression.Property(thisParameterExpression, propertieName); 180 MethodInfo method = typeof(string).GetMethod("Contains", new[] typeof(string) ); 181 var someValue = Expression.Constant(propertieValue, typeof(string)); 182 var containsMethodExp = Expression.Call(propertyExp, method, someValue); 183 return containsMethodExp; 184 185 186
以上就是一些基本的拼接都有了接下来是如何进行使用 我们还是贴上代码进行说明
class Program static void Main(string[] args) string[] nameArr = new string[] "just0ne", "kphui", "point" ; var userDataList = GetUserDataList().AsQueryable(); //初始化 var parameterExpression = Expression.Parameter(typeof(UserData)); var filter = (Expression)Expression.Constant(true); //寻找年岁大于10 filter = filter.And(parameterExpression.GotoGreaterThan<int>("Age", 10)); string key = Console.ReadLine(); if (!String.IsNullOrEmpty(key)) var keyFilter = (Expression)Expression.Constant(false); keyFilter = keyFilter.Or(parameterExpression.Contains("Name", key)); keyFilter = keyFilter.Or(parameterExpression.Contains("Phone", key)); filter = filter.And(keyFilter); filter = filter.And(parameterExpression.ContainsOperations("Name", nameArr)); var lamadaFilter = Expression.Lambda<Func<UserData, bool>>(filter, parameterExpression); var userDatas = userDataList.Where(lamadaFilter).ToList(); Console.WriteLine(Newtonsoft.Json.JsonConvert.SerializeObject(userDatas)); public static List<UserData> GetUserDataList() return new List<UserData>() new UserData() Age=18, Id=1, Name="just0ne", Phone="13856****26" , new UserData() Age=22, Id=2, Name="point", Phone="17521****52" , new UserData() Age=21, Id=3, Name="geekdog", Phone="15562****36" , new UserData() Age=14, Id=4, Name="kphui" , Phone="13577****26", new UserData() Age=13, Id=5, Name="lg" , Phone="13456****26", new UserData() Age=16, Id=6, Name="ming", Phone="13356****26" , new UserData() Age=18, Id=7, Name="tencent", Phone="13256****26" , new UserData() Age=10, Id=8, Name="justin" , Phone="13156****26", new UserData() Age=31, Id=9, Name="hujw", Phone="13823****26" , new UserData() Age=27, Id=10, Name="lqm" , Phone="13876****26", new UserData() Age=26, Id=11, Name="jiujiu" , Phone="13846****26", ; public class UserData public int Id get; set; public string Name get; set; public string Phone get; set; public string Email get; set; public int Age get; set;
我们运行程序会输出如下的内容:
以上只是针对如何使用表达式树做个例子 如有不同的可以留言哦！
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