访问嵌套属性从集合中的表达

Question

OK设置上下文一点使用表达式树使用这个类

public class HomeTableInvoice { 
    public int Sys_InvoiceID { get; set; } 
    public bool Turnover { get; set; } 
    public int FK_StatusID { get; set; } 
    public string InvoiceNumber { get; set; } 
    public DateTime InvoiceDate { get; set; } 
    public string DocType { get; set; } 

    public ICollection<InvoiceCustomFields> InvoiceCustomFields { get; set; } 
} 

我设法让一切工作我建立了一个动态的LINQ搜索子句和我用的参数是HomeTableInvoice，我可以使用

var parameter = Expression.Parameter(typeof(HomeTableInvoice), "invoice"); 
prop = Expression.Property(param, filter.SysName); 

与filter.SysName是我要过滤的字段得到一个表达式的属性。

当试图在底部为ICollection构建表达式时，问题就出现了。类InvoiceCustomFields包含

public class InvoiceCustomFields : CustomFieldsBase { 
     public int? FK_SysInvoiceID { get; set; }  
     public string FK_CustomFieldHeader { get; set; }  
     public string Value { get; set; }  
    } 

我试图访问FkCustomFieldHeader字符串和值字符串所以，当我查询例如条件可以像

where InvoiceNumber == 34 AndAlso (Invoice.InvoiceCustomField.FK_CustomFieldHeader == "Test" && Invoice.InvoiceCustomField.FK_CustomFieldHeader.Value == 42) 

我使用

尝试

prop = Expression.PropertyOrField(Expression.PropertyOrField(param, "InvoiceCustomFields"), "FK_CustomFieldHeader"); 

但它抛出这个错误

FK_CustomFieldHeader' is not a member of type 'System.Collections.Generic.ICollection`1[APData.Audit.Entityframework.Entities.InvoiceCustomFields]' 

任何的帮助深表感谢

- 编辑 -

由伊万试图回答后，我得到的错误

No generic method 'Any' on type 'System.Linq.Enumerable' is compatible with the supplied type arguments and arguments 

我又试图此

prop = Expression.PropertyOrField(parameter, "InvoiceCustomFields"); 

    var queryableType = typeof(Enumerable); 
    var whereMethod = queryableType.GetMethods() 
     .First(m => { 
     var parameters = m.GetParameters().ToList();        
      return m.Name == "Any" && m.IsGenericMethodDefinition && 
               parameters.Count == 2; 
         }); 

    MethodInfo methoInfo = whereMethod.MakeGenericMethod(prop.Type); 
    var x = Expression.Call(methoInfo, Expression.PropertyOrField(parameter, "InvoiceCustomFields"), whereQuery); 

而且然后抛出

Expression of type `'System.Collections.Generic.ICollection`1[InvoiceCustomFields]' cannot be used for parameter of type 'System.Linq.IQueryable`1[System.Collections.Generic.ICollection`1[InvoiceCustomFields]]' of method 'Boolean Any[ICollection`1](System.Linq.IQueryable`1[System.Collections.Generic.ICollection`1[InvoiceCustomFields]], System.Linq.Expressions.Expression`1[System.Func`2[System.Collections.Generic.ICollection`1[.InvoiceCustomFields],System.Boolean]])` 

Answer 1

让我们来看看它是不是动态的。以下内容：

Expression<Func<HomeTableInvoice, bool>> predicate = invoice => 
    invoice.InvoiceCustomField.FK_CustomFieldHeader == "Test" && 
    invoice.InvoiceCustomField.Value == "42"; 

不是一个有效的表达式。

你真正需要做的是这样的：

Expression<Func<HomeTableInvoice, bool>> predicate = invoice => 
    invoice.InvoiceCustomFields.Any(field => 
     field.InvoiceCustomField.FK_CustomFieldHeader == "Test" && 
     field.InvoiceCustomField.Value == "42"); 

这里是你如何构建动态（希望你可以调整它为您的需求与您的变量替换硬编码的部分）：

var parameter = Expression.Parameter(typeof(HomeTableInvoice), "invoice"); 

var fieldParameter = Expression.Parameter(typeof(InvoiceCustomFields), "field"); 
var anyPredicate = Expression.Lambda(
    Expression.AndAlso(
     Expression.Equal(
      Expression.PropertyOrField(fieldParameter, "FK_CustomFieldHeader"), 
      Expression.Constant("Test")), 
     Expression.Equal(
      Expression.PropertyOrField(fieldParameter, "Value"), 
      Expression.Constant("42"))), 
    fieldParameter); 
var fieldCondition = Expression.Call(
    typeof(Enumerable), "Any", new[] { fieldParameter.Type }, 
    Expression.PropertyOrField(parameter, "InvoiceCustomFields"), anyPredicate); 

// You can use the fieldCondition in your combinator, 
// the following is just to complete the example 
var predicate = Expression.Lambda<Func<HomeTableInvoice, bool>>(fieldCondition, parameter); 

// Test 
var input = new List<HomeTableInvoice> 
{ 
    new HomeTableInvoice 
    { 
     InvoiceNumber = "1", 
     InvoiceCustomFields = new List<InvoiceCustomFields> 
     { 
      new InvoiceCustomFields { FK_CustomFieldHeader = "Test", Value = "42" } 
     } 
    }, 
}.AsQueryable(); 
var output = input.Where(predicate).ToList();