C# Lambda 表达式学习之(一):得到一个类的字段(Field)或属性(Property)名,强类型得到
2012-06-29 00:27 音乐让我说 阅读(2493) 评论(0) 编辑 收藏 举报可能你还感兴趣:
1. C# Lambda 表达式学习之(一):得到一个类的字段(Field)或属性(Property)名,强类型得到
2. C# Lambda 表达式学习之(二):LambdaExpression 实战练习
3. 基于 Entity Framework FluentAPI 思想的强类型的 Lambda Expressions 实体映射
4. C# Lambda 表达式学习之(三):动态构建类似于 c => c.Age == null || c.Age > 18 的表达式
5. C# Lambda 表达式学习之(四):动态构建类似于 c => c.Age == 2 || c.Age == 5 || c => c.Age == 17 等等一个或多个 OrElse 的表达式
简单属性
所谓“简单属性”,是指一个类的属性的类型是基本数据类型(int、string、guid、datetime、float、decimal 等等)。
直接贴代码了:
using System; using System.Text; using System.Linq; using System.Linq.Expressions; using System.Collections.Generic; namespace DearBruce.ConAppTest { class Program { static void Main(string[] args) { string idStr = ExpressionHelper<UserInfo>.GetPropertyName(u => u.Id); Console.WriteLine(idStr); // 打印:"Id" string nameStr = ExpressionHelper<UserInfo>.GetPropertyName(u => u.Name); Console.WriteLine(nameStr); // 打印:"Name" Console.Read(); } } public class ExpressionHelper<T> where T : class, new() { /// <summary> /// 得到一个字段(Field)或属性(Property)名 /// </summary> /// <typeparam name="TProperty"></typeparam> /// <param name="express"></param> /// <returns></returns> public static string GetPropertyName<TProperty>(Expression<Func<T, TProperty>> express) { if (express == null) { throw new ArgumentNullException("express"); } MemberExpression memberExpression = express.Body as MemberExpression; if (memberExpression == null) { throw new ArgumentException("请为类型 \"" + typeof(T).FullName + "\" 的指定一个字段(Field)或属性(Property)作为 Lambda 的主体(Body)。"); } return memberExpression.Member.Name; } } class UserInfo { public int Id { get; set; } public string Name { get; set; } public DateTime DateOfBirth { get; set; } } }
我们换另一种方式
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Text.RegularExpressions; using System.Linq.Expressions; using System.Reflection; namespace MyApp.TestMvc.ConApp { class Program { static void Main(string[] args) { object obj = +5; Console.WriteLine(obj); // 打印 5 Product p = new Product(); string value1 = ExpressionHelper.GetPropertyName(() => p.ProductName); Console.WriteLine("value1:" + value1); // ProductName string value2 = ExpressionHelper.GetPropertyName<Product>(c => +c.Category_CategoryId.Id); Console.WriteLine("value2:" + value2); // Id p.ProductName = "我爱编程"; string tempPopName; object value3 = ExpressionHelper.GetPropertyNameAndValue(() => p.ProductName, out tempPopName); Console.WriteLine("value3:" + value3 + ", popName:" + tempPopName); // 我爱编程, ProductName } } public class Category { public int Id { get; set; } public string CateName { get; set; } } public class Product { public int Id { get; set; } public string ProductName { get; set; } public int CategoryId { get; set; } public Category Category_CategoryId { get; set; } } public class ExpressionHelper { public static string GetPropertyName(Expression<Func<object>> exp) { MemberExpression body = exp.Body as MemberExpression; if (body == null) { throw new InvalidOperationException("Not a member access."); } PropertyInfo member = body.Member as PropertyInfo; return member.Name; } public static string GetPropertyName<T>(Expression<Func<T, object>> exp) { MemberExpression body = null; if (exp.Body is MemberExpression) { body = exp.Body as MemberExpression; } if (exp.Body is UnaryExpression) { UnaryExpression expression2 = exp.Body as UnaryExpression; if (expression2.Operand is MemberExpression) { body = expression2.Operand as MemberExpression; } } if (body == null) { throw new InvalidOperationException("Not a member access."); } PropertyInfo member = body.Member as PropertyInfo; return member.Name; } public static object GetPropertyNameAndValue(Expression<Func<object>> exp, out string propName) { MemberExpression body = exp.Body as MemberExpression; PropertyInfo member = null; if (exp.Body is MemberExpression) { member = ((MemberExpression)exp.Body).Member as PropertyInfo; } else if (exp.Body is UnaryExpression) { member = ((MemberExpression)((UnaryExpression)exp.Body).Operand).Member as PropertyInfo; } object obj2 = exp.Compile().DynamicInvoke(new object[0]); propName = member.Name; return obj2; } } }
完毕!
复杂属性
所谓“复杂属性”,是指一个类的属性的类型是非基本数据类型,一般指类、嵌套类、接口等等。
下面的代码来自 https://github.com/MarlabsInc/SocialGoal
using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.Mvc; using System.Linq.Expressions; namespace SocialGoal.Web.Core { public static class HtmlExtensions { public static MvcHtmlString File(this HtmlHelper html, string name) { var tb = new TagBuilder("input"); tb.Attributes.Add("type", "file"); tb.Attributes.Add("name", name); tb.GenerateId(name); return MvcHtmlString.Create(tb.ToString(TagRenderMode.SelfClosing)); } public static MvcHtmlString FileFor<TModel, TProperty>(this HtmlHelper<TModel> html, Expression<Func<TModel, TProperty>> expression) { string name = GetFullPropertyName(expression); return html.File(name); } #region Helpers static string GetFullPropertyName<T, TProperty>(Expression<Func<T, TProperty>> exp) { MemberExpression memberExp; if (!TryFindMemberExpression(exp.Body, out memberExp)) return string.Empty; var memberNames = new Stack<string>(); do { memberNames.Push(memberExp.Member.Name); } while (TryFindMemberExpression(memberExp.Expression, out memberExp)); return string.Join(".", memberNames.ToArray()); } static bool TryFindMemberExpression(Expression exp, out MemberExpression memberExp) { memberExp = exp as MemberExpression; if (memberExp != null) return true; if (IsConversion(exp) && exp is UnaryExpression) { memberExp = ((UnaryExpression)exp).Operand as MemberExpression; if (memberExp != null) return true; } return false; } static bool IsConversion(Expression exp) { return (exp.NodeType == ExpressionType.Convert || exp.NodeType == ExpressionType.ConvertChecked); } #endregion } }
谢谢浏览!
作者:音乐让我说(音乐让我说 - 博客园)
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