扩展类
1 public static class LinqExtensions 2 { 3 /// <summary> 4 /// 创建lambda表达式：p=>true 5 /// </summary> 6 /// <typeparam name="T">对象名称（类名）</typeparam> 7 /// <returns></returns> 8 public static Expression<Func<T, bool>> True<T>() 9 { 10 return p => true; 11 } 12 13 /// <summary> 14 /// 创建lambda表达式：p=>false 15 /// </summary> 16 /// <typeparam name="T">对象名称（类名）</typeparam> 17 /// <returns></returns> 18 public static Expression<Func<T, bool>> False<T>() 19 { 20 return p => false; 21 } 22 23 /// <summary> 24 /// 创建lambda表达式：p=>p.propertyName 25 /// </summary> 26 /// <typeparam name="T">对象名称（类名）</typeparam> 27 /// <typeparam name="TKey">参数类型</typeparam> 28 /// <param name="propertyName">字段名称（数据库中字段名称）</param> 29 /// <returns></returns> 30 public static Expression<Func<T, TKey>> GetOrderExpression<T, TKey>(string propertyName) 31 { 32 ParameterExpression parameter = Expression.Parameter(typeof(T), "p"); 33 return Expression.Lambda<Func<T, TKey>>(Expression.Property(parameter, propertyName), parameter); 34 } 35 36 /// <summary> 37 /// 创建lambda表达式：p=>p.propertyName == propertyValue 38 /// </summary> 39 /// <typeparam name="T">对象名称（类名）</typeparam> 40 /// <param name="propertyName">字段名称（数据库中字段名称）</param> 41 /// <param name="propertyValue">数据值</param> 42 /// <returns></returns> 43 public static Expression<Func<T, bool>> CreateEqual<T>(string propertyName, object propertyValue, Type typeValue) 44 { 45 ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p 46 MemberExpression member = Expression.PropertyOrField(parameter, propertyName); 47 ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数 48 return Expression.Lambda<Func<T, bool>>(Expression.Equal(member, constant), parameter); 49 } 50 51 /// <summary> 52 /// 创建lambda表达式：p=>p.propertyName != propertyValue 53 /// </summary> 54 /// <typeparam name="T">对象名称（类名）</typeparam> 55 /// <param name="propertyName">字段名称（数据库中字段名称）</param> 56 /// <param name="propertyValue">数据值</param> 57 /// <returns></returns> 58 public static Expression<Func<T, bool>> CreateNotEqual<T>(string propertyName, object propertyValue, Type typeValue) 59 { 60 ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p 61 MemberExpression member = Expression.PropertyOrField(parameter, propertyName); 62 ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数 63 return Expression.Lambda<Func<T, bool>>(Expression.NotEqual(member, constant), parameter); 64 } 65 66 /// <summary> 67 /// 创建lambda表达式：p=>p.propertyName > propertyValue 68 /// </summary> 69 /// <typeparam name="T">对象名称（类名）</typeparam> 70 /// <param name="propertyName">字段名称（数据库中字段名称）</param> 71 /// <param name="propertyValue">数据值</param> 72 /// <returns></returns> 73 public static Expression<Func<T, bool>> CreateGreaterThan<T>(string propertyName, object propertyValue, Type typeValue) 74 { 75 ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p 76 MemberExpression member = Expression.PropertyOrField(parameter, propertyName); 77 ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数 78 return Expression.Lambda<Func<T, bool>>(Expression.GreaterThan(member, constant), parameter); 79 } 80 81 /// <summary> 82 /// 创建lambda表达式：p=>p.propertyName小于propertyValue 83 /// </summary> 84 /// <typeparam name="T">对象名称（类名）</typeparam> 85 /// <param name="propertyName">字段名称（数据库中字段名称）</param> 86 /// <param name="propertyValue">数据值</param> 87 /// <returns></returns> 88 public static Expression<Func<T, bool>> CreateLessThan<T>(string propertyName, object propertyValue, Type typeValue) 89 { 90 ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p 91 MemberExpression member = Expression.PropertyOrField(parameter, propertyName); 92 ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数 93 return Expression.Lambda<Func<T, bool>>(Expression.LessThan(member, constant), parameter); 94 } 95 96 /// <summary> 97 /// 创建lambda表达式：p=>p.propertyName >= propertyValue 98 /// </summary> 99 /// <typeparam name="T">对象名称（类名）</typeparam> 100 /// <param name="propertyName">字段名称（数据库中字段名称）</param> 101 /// <param name="propertyValue">数据值</param> 102 /// <returns></returns> 103 public static Expression<Func<T, bool>> CreateGreaterThanOrEqual<T>(string propertyName, object propertyValue, Type typeValue) 104 { 105 ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p 106 MemberExpression member = Expression.PropertyOrField(parameter, propertyName); 107 ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数 108 return Expression.Lambda<Func<T, bool>>(Expression.GreaterThanOrEqual(member, constant), parameter); 109 } 110 111 /// <summary> 112 /// 创建lambda表达式：p=> p.propertyName 小于= propertyValue 113 /// </summary> 114 /// <typeparam name="T">对象名称（类名）</typeparam> 115 /// <param name="propertyName">字段名称（数据库中字段名称）</param> 116 /// <param name="propertyValue">数据值</param> 117 /// <returns></returns> 118 public static Expression<Func<T, bool>> CreateLessThanOrEqual<T>(string propertyName, object propertyValue, Type typeValue) 119 { 120 ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p 121 MemberExpression member = Expression.PropertyOrField(parameter, propertyName); 122 ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数 123 return Expression.Lambda<Func<T, bool>>(Expression.LessThanOrEqual(member, constant), parameter); 124 } 125 126 /// <summary> 127 /// 创建lambda表达式：p=>p.propertyName.Contains(propertyValue) 128 /// </summary> 129 /// <typeparam name="T">对象名称（类名）</typeparam> 130 /// <param name="propertyName">字段名称（数据库中字段名称）</param> 131 /// <param name="propertyValue">数据值</param> 132 /// <returns></returns> 133 public static Expression<Func<T, bool>> GetContains<T>(string propertyName, string propertyValue) 134 { 135 ParameterExpression parameter = Expression.Parameter(typeof(T), "p"); 136 MemberExpression member = Expression.PropertyOrField(parameter, propertyName); 137 MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) }); 138 ConstantExpression constant = Expression.Constant(propertyValue, typeof(string)); 139 return Expression.Lambda<Func<T, bool>>(Expression.Call(member, method, constant), parameter); 140 } 141 142 /// <summary> 143 /// 创建lambda表达式：!(p=>p.propertyName.Contains(propertyValue)) 144 /// </summary> 145 /// <typeparam name="T">对象名称（类名）</typeparam> 146 /// <param name="propertyName">字段名称（数据库中字段名称）</param> 147 /// <param name="propertyValue">数据值</param> 148 /// <returns></returns> 149 public static Expression<Func<T, bool>> GetNotContains<T>(string propertyName, string propertyValue) 150 { 151 ParameterExpression parameter = Expression.Parameter(typeof(T), "p"); 152 MemberExpression member = Expression.PropertyOrField(parameter, propertyName); 153 MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) }); 154 ConstantExpression constant = Expression.Constant(propertyValue, typeof(string)); 155 return Expression.Lambda<Func<T, bool>>(Expression.Not(Expression.Call(member, method, constant)), parameter); 156 } 157 158 /// <summary> 159 /// 功能描述:拼接Or 160 /// 作 者:beck.huang 161 /// 创建日期:2018-11-30 15:35:10 162 /// 任务编号:好餐谋后台管理系统 163 /// </summary> 164 /// <param name="expression1">expression1</param> 165 /// <param name="expression2">expression2</param> 166 /// <returns>返回值</returns> 167 public static Expression<Func<T, bool>> Or<T>(Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2) 168 { 169 return Compose(expression1, expression2, Expression.OrElse); 170 } 171 172 /// <summary> 173 /// 功能描述:拼接And 174 /// 作 者:beck.huang 175 /// 创建日期:2018-11-30 15:35:18 176 /// 任务编号:好餐谋后台管理系统 177 /// </summary> 178 /// <param name="expression1">expression1</param> 179 /// <param name="expression2">expression2</param> 180 /// <returns>返回值</returns> 181 public static Expression<Func<T, bool>> And<T>(Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2) 182 { 183 return Compose(expression1, expression2, Expression.AndAlso); 184 } 185 186 /// <summary> 187 /// 功能描述:合并2个表达式 188 /// 作 者:beck.huang 189 /// 创建日期:2018-11-30 15:35:26 190 /// 任务编号:好餐谋后台管理系统 191 /// </summary> 192 /// <param name="first">first</param> 193 /// <param name="second">second</param> 194 /// <param name="merge">merge</param> 195 /// <returns>返回值</returns> 196 public static Expression<T> Compose<T>(Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge) 197 { 198 var map = first.Parameters 199 .Select((f, i) => new { f, s = second.Parameters[i] }) 200 .ToDictionary(p => p.s, p => p.f); 201 var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body); 202 return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters); 203 } 204 private class ParameterRebinder : ExpressionVisitor 205 { 206 readonly Dictionary<ParameterExpression, ParameterExpression> map; 207 /// <summary> 208 /// Initializes a new instance of the <see cref="ParameterRebinder"/> class. 209 /// </summary> 210 /// <param name="map">The map.</param> 211 ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map) 212 { 213 this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>(); 214 } 215 /// <summary> 216 /// Replaces the parameters. 217 /// </summary> 218 /// <param name="map">The map.</param> 219 /// <param name="exp">The exp.</param> 220 /// <returns>Expression</returns> 221 public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp) 222 { 223 return new ParameterRebinder(map).Visit(exp); 224 } 225 protected override Expression VisitParameter(ParameterExpression p) 226 { 227 ParameterExpression replacement; 228 229 if (map.TryGetValue(p, out replacement)) 230 { 231 p = replacement; 232 } 233 return base.VisitParameter(p); 234 } 235 } 236 }