Linq Expression.Property（param，field）是“trolling”me[System.ArgumentException]={“实例属性'B.Name'未为类型A定义”}

再一次，我面临一个问题，这次是使用LINQ Expression builder，这次我甚至在努力寻找它不起作用的原因。我有一个数据库第一EF项目与相当多的表。对于这个特定的案例，我必须使用其中的两个-DocHead和Contragent。MyService.metadata.cs如下所示：

[MetadataTypeAttribute(typeof(DocHead.DocHeadMetadata))]
public partial class DocHead
{

    // This class allows you to attach custom attributes to properties
    // of the DocHead class.
    //
    // For example, the following marks the Xyz property as a
    // required property and specifies the format for valid values:
    //    [Required]
    //    [RegularExpression("[A-Z][A-Za-z0-9]*")]
    //    [StringLength(32)]
    //    public string Xyz { get; set; }
    internal sealed class DocHeadMetadata
    {

        // Metadata classes are not meant to be instantiated.
        private DocHeadMetadata()
        {
        }

        public string doc_Code { get; set; }
        public string doc_Name { get; set; }
        public string doc_ContrCode { get; set; }
        //...

        [Include]
        public Contragent Contragent { get; set; }
    }
}

[MetadataTypeAttribute(typeof(Contragent.ContragentMetadata))]
public partial class Contragent
{

    // This class allows you to attach custom attributes to properties
    // of the Contragent class.
    //
    // For example, the following marks the Xyz property as a
    // required property and specifies the format for valid values:
    //    [Required]
    //    [RegularExpression("[A-Z][A-Za-z0-9]*")]
    //    [StringLength(32)]
    //    public string Xyz { get; set; }
    internal sealed class ContragentMetadata
    {

        // Metadata classes are not meant to be instantiated.
        private ContragentMetadata()
        {
        }

        public string Code { get; set; }
        public string Name { get; set; }
        //...

IQueryable<DocHead> docHeads = new MyEntities().DocHead;

docHeads = docHeads.OrderByDescending(x => x.Contragent.Name);

string field = "Contragent.Name";
string linq = "docHeads = docHeads.OrderByDescending(x => x." + field + ")";
IQueryable<DocHead> result = TheBestLinqLibraryInTheWorld.PrepareLinqQueryable(linq);

docHeads = docHeads.OrderByField<DocHead>("Contragent.Name", true); // true - let it be Ascending order

我拿了一些像这样的头像：

[MetadataTypeAttribute(typeof(DocHead.DocHeadMetadata))]
public partial class DocHead
{

    // This class allows you to attach custom attributes to properties
    // of the DocHead class.
    //
    // For example, the following marks the Xyz property as a
    // required property and specifies the format for valid values:
    //    [Required]
    //    [RegularExpression("[A-Z][A-Za-z0-9]*")]
    //    [StringLength(32)]
    //    public string Xyz { get; set; }
    internal sealed class DocHeadMetadata
    {

        // Metadata classes are not meant to be instantiated.
        private DocHeadMetadata()
        {
        }

        public string doc_Code { get; set; }
        public string doc_Name { get; set; }
        public string doc_ContrCode { get; set; }
        //...

        [Include]
        public Contragent Contragent { get; set; }
    }
}

[MetadataTypeAttribute(typeof(Contragent.ContragentMetadata))]
public partial class Contragent
{

    // This class allows you to attach custom attributes to properties
    // of the Contragent class.
    //
    // For example, the following marks the Xyz property as a
    // required property and specifies the format for valid values:
    //    [Required]
    //    [RegularExpression("[A-Z][A-Za-z0-9]*")]
    //    [StringLength(32)]
    //    public string Xyz { get; set; }
    internal sealed class ContragentMetadata
    {

        // Metadata classes are not meant to be instantiated.
        private ContragentMetadata()
        {
        }

        public string Code { get; set; }
        public string Name { get; set; }
        //...

IQueryable<DocHead> docHeads = new MyEntities().DocHead;

docHeads = docHeads.OrderByDescending(x => x.Contragent.Name);

string field = "Contragent.Name";
string linq = "docHeads = docHeads.OrderByDescending(x => x." + field + ")";
IQueryable<DocHead> result = TheBestLinqLibraryInTheWorld.PrepareLinqQueryable(linq);

docHeads = docHeads.OrderByField<DocHead>("Contragent.Name", true); // true - let it be Ascending order

一切都按照我想要的方式进行。我把那些头像按加入的反对者的名字分类。我的问题是，我必须按字段对它们进行排序，作为字符串参数给出。我需要能够写这样的东西：

[MetadataTypeAttribute(typeof(DocHead.DocHeadMetadata))]
public partial class DocHead
{

    // This class allows you to attach custom attributes to properties
    // of the DocHead class.
    //
    // For example, the following marks the Xyz property as a
    // required property and specifies the format for valid values:
    //    [Required]
    //    [RegularExpression("[A-Z][A-Za-z0-9]*")]
    //    [StringLength(32)]
    //    public string Xyz { get; set; }
    internal sealed class DocHeadMetadata
    {

        // Metadata classes are not meant to be instantiated.
        private DocHeadMetadata()
        {
        }

        public string doc_Code { get; set; }
        public string doc_Name { get; set; }
        public string doc_ContrCode { get; set; }
        //...

        [Include]
        public Contragent Contragent { get; set; }
    }
}

[MetadataTypeAttribute(typeof(Contragent.ContragentMetadata))]
public partial class Contragent
{

    // This class allows you to attach custom attributes to properties
    // of the Contragent class.
    //
    // For example, the following marks the Xyz property as a
    // required property and specifies the format for valid values:
    //    [Required]
    //    [RegularExpression("[A-Z][A-Za-z0-9]*")]
    //    [StringLength(32)]
    //    public string Xyz { get; set; }
    internal sealed class ContragentMetadata
    {

        // Metadata classes are not meant to be instantiated.
        private ContragentMetadata()
        {
        }

        public string Code { get; set; }
        public string Name { get; set; }
        //...

IQueryable<DocHead> docHeads = new MyEntities().DocHead;

docHeads = docHeads.OrderByDescending(x => x.Contragent.Name);

string field = "Contragent.Name";
string linq = "docHeads = docHeads.OrderByDescending(x => x." + field + ")";
IQueryable<DocHead> result = TheBestLinqLibraryInTheWorld.PrepareLinqQueryable(linq);

docHeads = docHeads.OrderByField<DocHead>("Contragent.Name", true); // true - let it be Ascending order

在My.edmx模型中，表DocHead和contracent已经为我建立了一个关系，如下所示：0..1到*

再一次，我在编写静态查询方面没有任何问题。我可以通过OrderByField方法创建动态的，但只有当涉及到类DocHead的属性时才可以。当我试图通过一个加入反政府阶级的支柱来订购时，灾难降临了。任何帮助都将不胜感激，谢谢

问题在于该方法不支持嵌套属性。它完全按照它所说的做-创建表达式，该表达式表示由表达式参数表示的对象的propertyName参数表示的属性

幸运的是，它可以很容易地扩展。需要创建嵌套属性访问表达式时，可以随时使用以下简单/技巧：

var prop = SortField.Split('.').Aggregate((Expression)param, Expression.Property);

问题是该方法不支持嵌套属性。它完全按照它所说的做-创建表达式，该表达式表示由表达式参数表示的对象的propertyName参数表示的属性

幸运的是，它可以很容易地扩展。需要创建嵌套属性访问表达式时，可以随时使用以下简单/技巧：

var prop = SortField.Split('.').Aggregate((Expression)param, Expression.Property);

---

我从来没有想过LINQ在欺骗我，但我对XAML有很多这种感觉。我从来没有想过LINQ在欺骗我，但我对XAML有很多这种感觉。谢谢你100%的工作解决方案！干杯@Ed Plunket——有时候，只是为了好玩，我用短语“is trolling me”替换“throws”，因为“throw”和“troll”发音非常相似。老实说，我尽最大努力避免为“tt-select中的from t”这样的数据编写linq查询，这种特殊的语法真的让我神魂颠倒使用lambdas的“普通”查询对我来说似乎更友好。感谢您100%的工作解决方案！干杯@Ed Plunket——有时候，只是为了好玩，我用短语“is trolling me”替换“throws”，因为“throw”和“troll”发音非常相似。老实说，我尽最大努力避免为“tt-select中的from t”这样的数据编写linq查询，这种特殊的语法真的让我神魂颠倒对我来说，lambdas的普通询问似乎更友好。