我有一个按对象字段对通用列表进行排序的方法:
public static IQueryable<T> SortTable<T>(IQueryable<T> q, string sortfield, bool ascending)
{
var p = Expression.Parameter(typeof(T), "p");
if (typeof(T).GetProperty(sortfield).PropertyType == typeof(int?))
{
var x = Expression.Lambda<Func<T, int?>>(Expression.Property(p, sortfield), p);
if (ascending)
q = q.OrderBy(x);
else
q = q.OrderByDescending(x);
}
else if (typeof(T).GetProperty(sortfield).PropertyType == typeof(int))
{
var x = Expression.Lambda<Func<T, int>>(Expression.Property(p, sortfield), p);
if (ascending)
q = q.OrderBy(x);
else
q = q.OrderByDescending(x);
}
else if (typeof(T).GetProperty(sortfield).PropertyType == typeof(DateTime))
{
var x = Expression.Lambda<Func<T, DateTime>>(Expression.Property(p, sortfield), p);
if (ascending)
q = q.OrderBy(x);
else
q = q.OrderByDescending(x);
}
// many more for every type
return q;
}
有什么方法可以将这些 if 折叠成一个通用语句吗?
主要问题是对于这部分
Expression.Lambda<Func<T, int>>
我不确定如何通用地编写它。
最佳答案
如果您将 Queryable.OrderBy
扩展为其定义,则您不必使用 Expression.Lambda
的通用重载:
public static IQueryable<T> SortTable<T>(
IQueryable<T> q, string sortfield, bool ascending)
{
var p = Expression.Parameter(typeof(T), "p");
var x = Expression.Lambda(Expression.Property(p, sortfield), p);
return q.Provider.CreateQuery<T>(
Expression.Call(typeof(Queryable),
ascending ? "OrderBy" : "OrderByDescending",
new Type[] { q.ElementType, x.Body.Type },
q.Expression,
x));
}
关于c# - 为通用列表创建排序函数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/2646703/