获取的财产，作为字符串，从防爆pression＆LT;＆Func键LT;的TModel，TProperty＆GT;＆GT;

本文介绍了获取的财产，作为字符串，从防爆pression＆LT;＆Func键LT;的TModel，TProperty＆GT;＆GT;的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我使用一些强类型的前pressions是得到系列化，让我的用户界面code有强类型的排序和搜索前pressions。这些类型的防爆pression＆LT; Func键＆LT;的TModel，TProperty＆GT;＆GT; 和用作这样的： SortOption.Field =（P = ＆GT; p.FirstName）; 。我已经得到这个工作完全为这个简单的例子。

在code，我使用的解析名字财产离开那里实际上是重复使用的，我们使用第三方产品的一些现有的功能和它的伟大工程，直到我们开始deeply-工作嵌套属性（ SortOption.Field =（p =＆GT; p.Address.State.Abbreviation）; ）。这code有一些非常不同的假设在需要支持深层嵌套的属性。

至于这code做什么，我真的不明白它，而不是改变了code，我想我应该从头开始编写此功能。但是，我不知道一个的好的方式做到这一点。我想我们可以做的事情比做toString（）和执行字符串解析更好。那么，这样做是为了处理琐碎和深度嵌套的情况下，一个好办法？

要求：

• 鉴于前pression P =＆GT; p.FirstName 我需要名字的字符串。
• 鉴于前pression P =＆GT; p.Address.State.Abbreviation 我需要的字符串Address.State.Abbreviation

虽然它不是一个回答我的问题很重要，我怀疑我的序列化/反序列化code可能是别人谁发现在未来的这个问题很有用，所以下面是。同样，这code是没有问题的重要 - 我只是想这可能帮助别人。需要注意的是 DynamicEx pression.ParseLambda 来自Dynamic LINQ 东西， Property.PropertyToString（）是这个问题是关于什么的。

///＆LT;总结＆gt;///这定义了一个框架，通过跨越序列层，排序逻辑被执行。///＆LT; /总结＆gt;///＆LT; typeparam名=的TModel＆gt;这是您要筛选对象的类型＆lt; / typeparam＆GT;///＆LT; typeparam NAME =TProperty＆gt;这是LT您过滤对象的属性＆; / typeparam＆GT;[Serializable接口]公共类SortOption＆LT;的TModel，TProperty＆GT; ：ISerializable的，其中的TModel：类{    ///＆LT;总结＆gt;    ///便捷构造。    ///＆LT; /总结＆gt;    ///＆LT; PARAM NAME =财产方式＆gt;排序酒店＆LT; /参数＆GT;    ///＆LT; PARAM NAME =isAscending＆gt;表示如果排序应升序或降序＆LT; /参数＆GT;    ///＆所述; PARAM NAME =优先权＆gt;表示的排序优先级，其中0是大于10℃的更高的优先级; /参数＆GT;    公共SortOption（前pression＆LT;＆Func键LT;的TModel，TProperty＆GT;＆GT;物业，布尔isAscending = TRUE，INT优先级= 0）    {        属性=财产;        IsAscending = isAscending;        优先级=优先权;    }    ///＆LT;总结＆gt;    ///默认构造函数。    ///＆LT; /总结＆gt;    公共SortOption（）        ：这个（空）    {    }    ///＆LT;总结＆gt;    ///这是在物体上的字段筛选。    ///＆LT; /总结＆gt;    公共防爆pression＆LT;＆Func键LT;的TModel，TProperty＆GT;＆GT;物业{搞定;组; }    ///＆LT;总结＆gt;    ///这表明，如果排序应升序或降序。    ///＆LT; /总结＆gt;    公共BOOL IsAscending {搞定;组; }    ///＆LT;总结＆gt;    ///这表示排序优先级，其中0是比10更高的优先级。    ///＆LT; /总结＆gt;    公众诠释优先{搞定;组; }    ISerializable的的＃区域实施    ///＆LT;总结＆gt;    ///这是反序列化SortOption时调用的构造函数。    ///＆LT; /总结＆gt;    保护SortOption（的SerializationInfo信息，的StreamingContext上下文）    {        IsAscending = info.GetBoolean（IsAscending）;        优先= info.GetInt32（优先级）;        //我们只是在属性名坚持这一点。因此，让我们重新从拉姆达防爆pression。        属性= DynamicEx pression.ParseLambda＆LT;的TModel，TProperty＆GT;（info.GetString（「该物业」），默认（的TModel），默认（TProperty））;    }    ///＆LT;总结＆gt;    ///填充一个＆LT;见CREF =T：System.Runtime.Serialization.SerializationInfo/＆GT;用序列化目标对象所需的数据。    ///＆LT; /总结＆gt;    ///＆LT; PARAM NAME =信息＆GT;的＆lt;见CREF =T：System.Runtime.Serialization.SerializationInfo/＆GT;来填充数据。 ＆LT; /参数＆GT;    ///＆LT; PARAM NAME =背景＆gt;在目的地（参见LT;见CREF =T：System.Runtime.Serialization.StreamingContext/＆）对于此序列化。 ＆LT; /参数＆GT;    公共无效GetObjectData使用（的SerializationInfo信息，的StreamingContext上下文）    {        //在那里只要坚持属性名称。我们将基于在另一端重建前pression。        info.AddValue（属性，Property.PropertyToString（））;        info.AddValue（IsAscending，IsAscending）;        info.AddValue（优先级，优先）;    }    #endregion}

解决方案

下面的诀窍：这种形式的任何前pression ...

的obj =＆GT; obj.A.B.C //等。

...实际上只是一堆嵌套的 MemberEx pression 的对象。

首先你得：

MemberEx pression：obj.A.B.C防爆pression：// obj.A.B MemberEx pression会员：C

评估防爆pression 上面的为 MemberEx pression 的为您提供：

MemberEx pression：obj.A.B防爆pression：// obj.A MemberEx pression会员：乙

最后，上面的是的（在顶），你有：

MemberEx pression：obj.A防爆pression：OBJ //注意：不是MemberEx pression会员：一

因此​​，似乎很清楚，要解决这个问题的方法是通过检查的在防爆pression 属性 MemberEx pression ，直到它不再是本身的点 MemberEx pression 。

更新：似乎有对你的问题的补充旋。这可能是因为你有一些拉姆达的看起来的像 Func键＆LT; T，INT＆GT; ...

P =＆GT;页

...但的实际的一个 Func键＆LT; T，对象＆gt; ;在这种情况下，编译器将上述前pression转换为：

P =＆GT;转换（p.Age）

调整为这个问题其实并不一样坚韧，因为它看起来。看看我的更新code为对付它的方法之一。请注意，通过抽象code为得到一个 MemberEx pression 掳到其自己的方法（ TryFindMemberEx pression ），这种方法保持了 GetFullPropertyName 方法还算干净，并允许您在将来添加额外的检查 - 如果，也许，你会发现自己面临着的新的的，你没有原先占的场景 - 而不必通过太多code涉水

要说明：此code为我工作

// code调整为prevent水平溢出静态字符串GetFullPropertyName＆LT; T，TProperty＆GT;（防爆pression＆LT;＆Func键LT; T，TProperty＆GT;＆GT; EXP）{    MemberEx pression memberExp;    如果（！TryFindMemberEx pression（exp.Body，出memberExp））        返回的String.Empty;    VAR memberNames =新的堆栈＆LT;串GT;（）;    做    {        memberNames.Push（memberExp.Member.Name）;    }    而（TryFindMemberEx pression（memberExp.Ex pression，出memberExp））;    返回的string.join（，memberNames.ToArray（）。）;}// code调整为prevent水平溢出私人静态布尔TryFindMemberEx pression（防爆pression EXP，出MemberEx pression memberExp）{    memberExp = EXP作为MemberEx pression;    如果（memberExp！= NULL）    {        // heyo！这是很容易做到        返回true;    }    //如果编译器创建的自动转换，    //它会是这个样子？    // OBJ =＆GT;转换（obj.Property）[例如，INT - ＆GT;目的]    // 要么：    // OBJ =＆GT; ConvertChecked（obj.Property）[例如，INT - ＆GT;长]    // ...这是在IsConversion检查情况    如果（IsConversion（实验）及＆放大器; exp为UnaryEx pression）    {        memberExp =（（UnaryEx pression）EXP）.Operand作为MemberEx pression;        如果（memberExp！= NULL）        {            返回true;        }    }    返回false;}私人静态布尔IsConversion（前pression EXP）{    返回（        exp.NodeType ==防爆pressionType.Convert ||        exp.NodeType ==防爆pressionType.ConvertChecked    ）;}

用法：

防爆pression＆LT;＆Func键LT;人，串GT;＆GT; simpleExp = P =＆GT; p.FirstName;防爆pression＆LT;＆Func键LT;人，串GT;＆GT; complexExp = P =＆GT; p.Address.State.Abbreviation;防爆pression＆LT;＆Func键LT;人，对象＆gt;＆GT; ageExp = P =＆GT;页;Console.WriteLine（GetFullPropertyName（simpleExp））;Console.WriteLine（GetFullPropertyName（complexExp））;Console.WriteLine（GetFullPropertyName（ageExp））;

输出：

姓Address.State.Abbreviation年龄

I use some strongly-typed expressions that get serialized to allow my UI code to have strongly-typed sorting and searching expressions. These are of type Expression<Func<TModel,TProperty>> and are used as such: SortOption.Field = (p => p.FirstName);. I've gotten this working perfectly for this simple case.

The code that I'm using for parsing the "FirstName" property out of there is actually reusing some existing functionality in a third-party product that we use and it works great, until we start working with deeply-nested properties(SortOption.Field = (p => p.Address.State.Abbreviation);). This code has some very different assumptions in the need to support deeply-nested properties.

As for what this code does, I don't really understand it and rather than changing that code, I figured I should just write from scratch this functionality. However, I don't know of a good way to do this. I suspect we can do something better than doing a ToString() and performing string parsing. So what's a good way to do this to handle the trivial and deeply-nested cases?

Requirements:

• Given the expression p => p.FirstName I need a string of "FirstName".
• Given the expression p => p.Address.State.Abbreviation I need a string of "Address.State.Abbreviation"

While it's not important for an answer to my question, I suspect my serialization/deserialization code could be useful to somebody else who finds this question in the future, so it is below. Again, this code is not important to the question - I just thought it might help somebody. Note that DynamicExpression.ParseLambda comes from the Dynamic LINQ stuff and Property.PropertyToString() is what this question is about.

/// <summary> /// This defines a framework to pass, across serialized tiers, sorting logic to be performed. /// </summary> /// <typeparam name="TModel">This is the object type that you are filtering.</typeparam> /// <typeparam name="TProperty">This is the property on the object that you are filtering.</typeparam> [Serializable] public class SortOption<TModel, TProperty> : ISerializable where TModel : class { /// <summary> /// Convenience constructor. /// </summary> /// <param name="property">The property to sort.</param> /// <param name="isAscending">Indicates if the sorting should be ascending or descending</param> /// <param name="priority">Indicates the sorting priority where 0 is a higher priority than 10.</param> public SortOption(Expression<Func<TModel, TProperty>> property, bool isAscending = true, int priority = 0) { Property = property; IsAscending = isAscending; Priority = priority; } /// <summary> /// Default Constructor. /// </summary> public SortOption() : this(null) { } /// <summary> /// This is the field on the object to filter. /// </summary> public Expression<Func<TModel, TProperty>> Property { get; set; } /// <summary> /// This indicates if the sorting should be ascending or descending. /// </summary> public bool IsAscending { get; set; } /// <summary> /// This indicates the sorting priority where 0 is a higher priority than 10. /// </summary> public int Priority { get; set; } #region Implementation of ISerializable /// <summary> /// This is the constructor called when deserializing a SortOption. /// </summary> protected SortOption(SerializationInfo info, StreamingContext context) { IsAscending = info.GetBoolean("IsAscending"); Priority = info.GetInt32("Priority"); // We just persisted this by the PropertyName. So let's rebuild the Lambda Expression from that. Property = DynamicExpression.ParseLambda<TModel, TProperty>(info.GetString("Property"), default(TModel), default(TProperty)); } /// <summary> /// Populates a <see cref="T:System.Runtime.Serialization.SerializationInfo"/> with the data needed to serialize the target object. /// </summary> /// <param name="info">The <see cref="T:System.Runtime.Serialization.SerializationInfo"/> to populate with data. </param> /// <param name="context">The destination (see <see cref="T:System.Runtime.Serialization.StreamingContext"/>) for this serialization. </param> public void GetObjectData(SerializationInfo info, StreamingContext context) { // Just stick the property name in there. We'll rebuild the expression based on that on the other end. info.AddValue("Property", Property.PropertyToString()); info.AddValue("IsAscending", IsAscending); info.AddValue("Priority", Priority); } #endregion }

解决方案

Here's the trick: any expression of this form...

obj => obj.A.B.C // etc.

...is really just a bunch of nested MemberExpression objects.

First you've got:

MemberExpression: obj.A.B.C Expression: obj.A.B // MemberExpression Member: C

Evaluating Expression above as a MemberExpression gives you:

MemberExpression: obj.A.B Expression: obj.A // MemberExpression Member: B

Finally, above that (at the "top") you have:

MemberExpression: obj.A Expression: obj // note: not a MemberExpression Member: A

So it seems clear that the way to approach this problem is by checking the Expression property of a MemberExpression up until the point where it is no longer itself a MemberExpression.

UPDATE: It seems there is an added spin on your problem. It may be that you have some lambda that looks like a Func<T, int>...

p => p.Age

...but is actually a Func<T, object>; in this case, the compiler will convert the above expression to:

p => Convert(p.Age)

Adjusting for this issue actually isn't as tough as it might seem. Take a look at my updated code for one way to deal with it. Notice that by abstracting the code for getting a MemberExpression away into its own method (TryFindMemberExpression), this approach keeps the GetFullPropertyName method fairly clean and allows you to add additional checks in the future -- if, perhaps, you find yourself facing a new scenario which you hadn't originally accounted for -- without having to wade through too much code.

To illustrate: this code worked for me.

// code adjusted to prevent horizontal overflow static string GetFullPropertyName<T, TProperty> (Expression<Func<T, TProperty>> exp) { MemberExpression memberExp; if (!TryFindMemberExpression(exp.Body, out memberExp)) return string.Empty; var memberNames = new Stack<string>(); do { memberNames.Push(memberExp.Member.Name); } while (TryFindMemberExpression(memberExp.Expression, out memberExp)); return string.Join(".", memberNames.ToArray()); } // code adjusted to prevent horizontal overflow private static bool TryFindMemberExpression (Expression exp, out MemberExpression memberExp) { memberExp = exp as MemberExpression; if (memberExp != null) { // heyo! that was easy enough return true; } // if the compiler created an automatic conversion, // it'll look something like... // obj => Convert(obj.Property) [e.g., int -> object] // OR: // obj => ConvertChecked(obj.Property) [e.g., int -> long] // ...which are the cases checked in IsConversion if (IsConversion(exp) && exp is UnaryExpression) { memberExp = ((UnaryExpression)exp).Operand as MemberExpression; if (memberExp != null) { return true; } } return false; } private static bool IsConversion(Expression exp) { return ( exp.NodeType == ExpressionType.Convert || exp.NodeType == ExpressionType.ConvertChecked ); }

Usage:

Expression<Func<Person, string>> simpleExp = p => p.FirstName; Expression<Func<Person, string>> complexExp = p => p.Address.State.Abbreviation; Expression<Func<Person, object>> ageExp = p => p.Age; Console.WriteLine(GetFullPropertyName(simpleExp)); Console.WriteLine(GetFullPropertyName(complexExp)); Console.WriteLine(GetFullPropertyName(ageExp));

Output:

FirstName Address.State.Abbreviation Age