NPoco.Linq的OrderBy扩展方法 [英] OrderBy extension method for NPoco.Linq

问题描述

我想使用OrderBy("columnName").

I want to use OrderBy("columnName").

我发现可以通过编写扩展方法或使用反射来实现.

I see that it is possible by writing an extension method or using reflection.

我正在使用NPoco，并且无法编写扩展方法.

I am using NPoco and I am unable to write an extension method.

IQueryProvider<Sample> query =  DbConnection.Query<Sample>();

我想做

var res = query.OrderByField("columnName");

我想使用与此类似的东西:

I want to use something similar to this:

public static IQueryable<T> OrderByField<T>(this IQueryable<T> q, string SortField, bool Ascending)
{
    var param = Expression.Parameter(typeof(T), "p");
    var prop = Expression.Property(param, SortField);
    var exp = Expression.Lambda(prop, param);
    string method = Ascending ? "OrderBy" : "OrderByDescending";
    Type[] types = new Type[] { q.ElementType, exp.Body.Type };
    var mce = Expression.Call(typeof(Queryable), method, types, q.Expression, exp);
}

由于我传递的是IQueryProvider而不是IQueryable，因此上述方法不起作用.

The above wont work since I am passing IQueryProvider instead of IQueryable.

推荐答案

尝试以下代码

public static IQueryProvider<T> OrderByField<T>(this IQueryProvider<T> q, string SortField, bool Ascending)
{
    var param = Expression.Parameter(typeof(T), "p");
    var prop = Expression.Property(param, SortField);
    string methodName = Ascending ? "OrderBy" : "OrderByDescending";
    Expression conversion = Expression.Convert(prop, typeof(object));
    LambdaExpression lambda = Expression.Lambda(conversion, param);
    object result = typeof(IQueryProvider<T>).GetMethods().Single(
            method => method.Name == methodName)
        .Invoke(q, new object[] { lambda });
    return (IQueryProvider<T>)result;
}

然后应用查询.

var list = db.Query<Users>().OrderByField("Id",false).ToList();

这篇关于NPoco.Linq的OrderBy扩展方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！