在非泛型DbSet上应用动态构建的表达式

1 回答

• 1

  下面是一个可能对你有帮助的代码：它最终会创建一个myu的IQueryable，它实际上表示像SELECT * FROM YourMappedTable WHERE Id = 1但是cource，而不是使用我为演示目的而构建的表达式，你可以使用你的表达 .

  class Program
  {
      static void Main(string[] args)
      {
          using (var x = new DB01Entities ())
          {
              Type myType = typeof(Angajati);
  
              var setMethod = typeof(DB01Entities).GetMethods(System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.Public).Where (a => a.Name == "Set" && a.IsGenericMethod).First ().GetGenericMethodDefinition ();
  
              var mySet = setMethod.MakeGenericMethod(myType);
  
              var realSet = mySet.Invoke(x, null);
  
              var param1 = Expression.Parameter(myType, "param1");
  
              var propertyExpresion = Expression.Property(param1, "Id");
  
              var idExpresssion = Expression.Constant(1);
  
              var body = Expression.Equal(propertyExpresion, idExpresssion);
  
              var lambda = Expression.Lambda(body, param1);
  
              var genericTypeCaster = typeof(Program).GetMethod("Caster", System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.NonPublic).GetGenericMethodDefinition();
  
              var effectiveMethod = genericTypeCaster.MakeGenericMethod(myType);
  
              var filteredQueryable = effectiveMethod.Invoke(null, new Object[] {realSet, lambda });
          }
      }
  
      private static IQueryable<T> Caster <T> (DbSet<T> theSet, Expression whereCondition) where T : class
      {
          return theSet.Where(whereCondition as Expression<Func<T, bool>>);
      }
  }
  

  所以上面的“lambda”变量等同于你的“myFilter” . 它必须在运行时

  Expression<Func<YourType, bool>>.
  

  mySet是你的“实体”DbSet . 快乐的编码！

  回复于 2024-04-24T00:41:39+08:00