c# - 如何知道是否应用了 OrderBy 进行查询？

Question

在应用 .Skip 或 .Take 之前，我需要知道是否将 OrderBy 应用于 Linq 查询。我无法控制接收到的查询，如果应用了 OrderBy，我需要维护这个，在任何其他情况下我应该 OrderBy(t=>true)。我尝试了以下方法:

    DataContext db;
    var query = db.Orders;

    var wasOrderByApplied = typeof(IOrderedQueryable<Order>).IsAssignableFrom(query.AsQueryable().Expression.Type);
    var wasOrderByApplied2 = query.AsQueryable().Expression.Type == typeof(System.Data.Entity.Core.Objects.ObjectQuery<Order>);
    var wasOrderByApplied3 = typeof(IOrderedQueryable<Order>) == query.AsQueryable().Expression.Type;

    var query2 = db.Orders.OrderBy(o => o.CreationDate);

    var wasOrderByApplied4 = typeof(IOrderedQueryable<Order>).IsAssignableFrom(query2.AsQueryable().Expression.Type);
    var wasOrderByApplied5 = query2.AsQueryable().Expression.Type == typeof(System.Data.Entity.Core.Objects.ObjectQuery<Order>);
    var wasOrderByApplied6 = typeof(IOrderedQueryable<Order>) == query2.AsQueryable().Expression.Type;

    var query3 = db.Orders.OrderBy(o => o.CreationDate).Where(o => o.Id > 4);

    var wasOrderByApplied7 = typeof(IOrderedQueryable<Order>).IsAssignableFrom(query3.AsQueryable().Expression.Type);
    var wasOrderByApplied8 = query3.AsQueryable().Expression.Type == typeof(System.Data.Entity.Core.Objects.ObjectQuery<Order>);
    var wasOrderByApplied9 = typeof(IOrderedQueryable<Order>) == query3.AsQueryable().Expression.Type;

结果:

wasOrderByApplied = true;
wasOrderByApplied2 = true;
wasOrderByApplied3 = false;

wasOrderByApplied4 = true;
wasOrderByApplied5 = false;
wasOrderByApplied6 = true;

根据最后的结果，似乎对每个查询提出的第三个问题是正确的，但后来我做了第三个查询 (query3)，结果如下:

wasOrderByApplied7 = false;
wasOrderByApplied8 = false;
wasOrderByApplied9 = false;

当我在 OrderBy 之后添加 Where 时，问题结果是 false 而它应该是 true。

是否有更好的方法来了解查询是否应用了 OrderBy？

Answer 1

这是我想到的一种可能的解决方案:

创建一个表达式访问者，检查表达式是否调用 OrderBy 或 OrderByDescending 方法，如下所示:

public class MyVisitor : ExpressionVisitor
{
    public bool HasOrderBy { get; private set; }

    protected override Expression VisitMethodCall(MethodCallExpression node)
    {
        if (node.Method.DeclaringType == typeof (Queryable) &&
            (node.Method.Name == "OrderBy" || node.Method.Name == "OrderByDescending"))
            HasOrderBy = true;

        return base.VisitMethodCall(node);
    }
}

这里是你如何使用它:

MyVisitor visitor = new MyVisitor();

visitor.Visit(query.Expression);

if (visitor.HasOrderBy)
{
    //..
}
else
{
    //..
}