怎样申请的OrderBy在一个IQueryable中的一个通用的扩展方法使用一个字符串列名? [英] How do I apply OrderBy on an IQueryable using a string column name within a generic extension method?
问题描述
public static IQueryable<TResult> ApplySortFilter<T, TResult>(this IQueryable<T> query, string columnName)
where T : EntityObject
{
var param = Expression.Parameter(typeof(T), "o");
var body = Expression.PropertyOrField(param,columnName);
var sortExpression = Expression.Lambda(body, param);
return query.OrderBy(sortExpression);
}
由于为排序依据的类型不是从SORTEX pression推断我需要指定它是这样的,在运行时:
Because the type for OrderBy is not inferred from sortExpression I need to specify it something like this at run time:
var sortExpression = Expression.Lambda<T, TSortColumn>(body, param);
或
return query.OrderBy<T, TSortColumn>(sortExpression);
我不认为这是可能的但作为TSortColumn只能在运行时确定。
I don't think this is possible however as TSortColumn can only be determined during runtime.
有没有解决的办法吗?
推荐答案
我们没有类似的东西(不是100%相同,但大同小异)在LINQ to SQL中的项目。这里的code:
We did something similar (not 100% the same, but similar) in a LINQ to SQL project. Here's the code:
public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string ordering, params object[] values) {
var type = typeof(T);
var property = type.GetProperty(ordering);
var parameter = Expression.Parameter(type, "p");
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var orderByExp = Expression.Lambda(propertyAccess, parameter);
MethodCallExpression resultExp = Expression.Call(typeof(Queryable), "OrderBy", new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExp));
return source.Provider.CreateQuery<T>(resultExp);
}
我们实际上并没有使用一个通用的,我们有一个已知的类,但它应该在一个通用的(我已经把通用占位符,它应该是)。
We didn't actually use a generic, we had a known class, but it should work on a generic (I've put the generic placeholder where it should be).
编辑:对于降序排列,传递 OrderByDescending
而不是排序依据:
For descending order, pass in OrderByDescending
instead of "OrderBy":
MethodCallExpression resultExp = Expression.Call(typeof(Queryable), "OrderByDescending", new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExp));
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