如何知道是否应用于排序依据查询？ [英] How to know if OrderBy was applied to query?

问题描述

我需要知道，如果排序依据是施加.Skip或之前。取应用到LINQ查询。我没有接收到查询的控制，如果被施加的OrderBy我需要保持这一个，在其他任何情况下，我应该排序依据（T => TRUE）。我曾尝试以下内容：

I need to know if an OrderBy was applied to a Linq query before applying an .Skip or .Take. I have no control of the received query and if an OrderBy was applied I need to maintain this one, in any other case I should OrderBy(t=>true). I have tried the following:

    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;

结果其中：

The results where:

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

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

随着最后的结果似乎是要求每个查询的第三个问题是，一个是正确的，但后来我做了第三个查询（QUERY3），结果其中：

With the last results it seems that the third question asked to each query is the one that is correct, but then I did the third query (query3) and the results where:

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

在我的排序依据后添加在哪里的问题结果的假其中它应该是的真正

When I add a Where after the OrderBy the question result is false where it should be true.

有没有更好的办法知道如果排序依据是应用于查询？

Is there a better way to know if an OrderBy was applied to the query?

推荐答案

下面是来到我的心中只有一个可能的解决方案：

Here is one possible solution that came to my mind:

创建表达式游客支票该表达式是否调用排序依据，或者类似这样的 OrderByDescending 方法：

Create an expression visitor that checks whether the expression invokes the OrderBy, or the OrderByDescending method like this:

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);
    }
}

下面是如何使用它：

MyVisitor visitor = new MyVisitor();

visitor.Visit(query.Expression);

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

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