1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 using System.Linq.Expressions; 6 7 namespace Test 8 { 9 /// <summary> 10 /// 一個老外寫的擴充Expression方法的靜態類別,可以解決上面冗長的程式碼 11 /// </summary> 12 public static class DynamicLinqExpressions//注意static靜態型別 13 { 14 public static Expression<Func<T, bool>> True<T>() { return f => true; } 15 public static Expression<Func<T, bool>> False<T>() { return f => false; } 16 17 //注意this 18 public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1, 19 Expression<Func<T, bool>> expr2) 20 { 21 var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>()); 22 return Expression.Lambda<Func<T, bool>> 23 (Expression.Or(expr1.Body, invokedExpr), expr1.Parameters); 24 } 25 26 public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1, 27 Expression<Func<T, bool>> expr2) 28 { 29 var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>()); 30 return Expression.Lambda<Func<T, bool>> 31 (Expression.And(expr1.Body, invokedExpr), expr1.Parameters); 32 } 33 } 34 }
使用示例：
1 SchoolContainer school = new SchoolContainer(); 2 var eps = DynamicLinqExpressions.True<Teacher>(); 3 eps.And(T=>T.Name.Contains("1")); 4 var ss = school.Teacher.Where(T => T.Name.Contains("PM")).Where(eps); 5 foreach (var item in ss) 6 { 7 Console.WriteLine(item.Name); 8 }