Question

以下是Generic Repository存储OrderBy的方式：

private Func<IQueryable<T>, IOrderedQueryable<T>> _orderBy;

这里的Microsoft的OrderBy采用了一串字段名称（来自Microsoft's Dynamic Linq）：

public static IQueryable<T> OrderBy<T>(
    this IQueryable<T> source, 
    string ordering, params object[] values);

这是我们的扩展方法，它将我们的字段数组转换为逗号分隔的OrderBy / ThenBy：

public static IQueryable<T> OrderBy<T>(
    this IQueryable<T> source,
    ICollection<string> orderBy)
{    
    return source.OrderBy( String.Join(",", orderBy) );
}

一切正常，但需要将OrderBy附加到原始实体。 我们如何将OrderBy保存在变量中以便稍后附加到该实体？

//Something like 
Func<IQueryable<T>, IOrderedQueryable<T>> _orderBy = ??

供参考，这里是Microsoft的System.Linq.Dynamic.DynamicQueryable.OrderBy源代码（Scott G's writeup link）：

public static IQueryable<T> OrderBy<T>(
    this IQueryable<T> source, string ordering, params object[] values) 
{
    return (IQueryable<T>)OrderBy((IQueryable)source, ordering, values);
}

public static IQueryable OrderBy(
    this IQueryable source, string ordering, params object[] values) 
{
    if (source == null) throw new ArgumentNullException("source");
    if (ordering == null) throw new ArgumentNullException("ordering");
    ParameterExpression[] parameters = new ParameterExpression[] 
    {
        Expression.Parameter(source.ElementType, "") 
    };
    ExpressionParser parser = new ExpressionParser(parameters, ordering, values);
    IEnumerable<DynamicOrdering> orderings = parser.ParseOrdering();
    Expression queryExpr = source.Expression;
    string methodAsc = "OrderBy";
    string methodDesc = "OrderByDescending";
    foreach (DynamicOrdering o in orderings) 
    {
        queryExpr = Expression.Call(
            typeof(Queryable), 
            o.Ascending ? methodAsc : methodDesc,
            new Type[] { source.ElementType, o.Selector.Type },
            queryExpr,
            Expression.Quote(Expression.Lambda(o.Selector, parameters)));
        methodAsc = "ThenBy";
        methodDesc = "ThenByDescending";
    }
    return source.Provider.CreateQuery(queryExpr);
}

Answer 1

这是你想要的吗？

Func<IQueryable<T>, IOrderedQueryable<T>> _orderBy = t => t.OrderBy( String.Join(",", orderBy));

如何在变量中存储Microsoft的Dynamic Linq的OrderBy？

1 个答案: