Select 在 EF6 中加载相关数据不起作用时包含在里面

Question

我对 EF 6 有疑问。我的数据模型 class 中有以下语句，用于获取所有发票及其相关数据（PurchaseItems、Customer 和 CustomerAddress）。

public List<Invoice> GetAllInvoice()
    {
        using (var context = new InvoiceSolutionContext())
        {
           return context.Invoices.Include(p => p.PurchaseItems).Include(c => c.Customer.Select(ca => ca.CustomerAddress)).ToList();

        }
    }

上述方法在class.
中有如下using语句使用 Invoicing.DomainModel；
使用 System.Collections.Generic;
使用 System.Data.Entity;
使用 System.Linq;

但问题是，Select(ca => ca.CustomerAddress) 无法正常工作，并出现以下编译错误。

'Customer' does not contain a definition for 'Select' and no accessible extension method 'Select' accepting a first argument of type 'Customer' could be found (are you missing a using directive or an assembly reference?)

以下是与上述问题相关的 class。

 public class Invoice 
{      
    [Key]
    public int ID { get; set; }        

    [Required]
    [Column("invoiceNumber")]
    [Display(Name = "Invoice Number")]
    public string InvoiceNumber { get; set; }       

    [Required]
    [Column("description")]
    public string Description { get; set; }

    [Required]
    public List<PurchaseItem> PurchaseItems { get; set; }

    [Required]
    [Column("totalCost")]
    [Display(Name = "Total Cost")]
    public decimal TotalCost { get; set; }

    [Required]
    [Column("taxTotal")]
    [Display(Name = "Tax Amount")]
    public decimal TaxAmount { get; set; }

    [Column("otherCost")]
    [Display(Name = "Other Cost")]
    public decimal OtherCost { get; set; }

    [Required]
    [Column("subTotal")]
    [Display(Name = "Sub Total")]
    public decimal SubTotal { get; set; }


    #region Foreign Key Ref

    [Column("customerID")]
    public int CustomerID { get; set; }       

    public Customer Customer { get; set; }

    [Column("accountID")]
    public int AccountID { get; set; }

    public Account Account { get; set; }

    #endregion

    [Column("dateCreated")]
    public DateTime DateCreated { get; set; }

    [Column("dateModified")]
    public DateTime DateModified { get; set; }

    [Column("status")]
    public bool Status { get; set; }
}

public class PurchaseItem 
{
    [Key]
    public int ID { get; set; }

    [Required]
    [Column("description")]
    public string Description { get; set; }

    [Required]
    [Column("unitPrice")]
    [Display(Name = "Unit Price")]
    public decimal UnitPrice { get; set; }

    [Required]
    [Column("quantity")]
    public int Quantity { get; set; }

    [Required]
    [Column("amount")]
    public decimal Amount { get; set; }

    //foreign key reference
    [Column("invoiceID")]
    public int InvoiceID { get; set; }

    public Invoice Invoice { get; set; }

}

    public class Customer
{    
    [Key]
    public int ID { get; set; }     

    [Required]
    [Column("firstName")]
    [MaxLength(250, ErrorMessage ="First name must have 250 characters or less")]
    [Display(Name ="First Name")]
    public string FirstName { get; set; }        

    [Required]
    [Column("lastName")]
    [MaxLength(250, ErrorMessage ="Last name must have 250 characters or less")]
    [Display(Name ="Last Name")]
    public string LastName { get; set; }

    [Required]
    [Column("emailAddress")]
    [MaxLength(255, ErrorMessage ="Email address must have 255 characters or less")]
    [DataType(DataType.EmailAddress)] 
    [Display(Name = "Email Address")] 
    public string EmailAddress { get; set; }

    [Required]
    [Column("contactNumber")]
    [Display(Name ="Contact Number")]
    public string ContactNumber { get; set; }

    [Column("abn")]
    public string ABN { get; set; }

    [Column("dateCreated")]
    public DateTime DateCreated { get; set; }

    [Column("dateModified")]
    public DateTime DateModified { get; set; }

    [Column("status")]
    public bool Status { get; set; }

    public List<Invoice> Invoices { get; set; }

    public CustomerAddress CustomerAddress { get; set; }

}

public class CustomerAddress
{
    [Key, ForeignKey("Customer")]
    public int ID { get; set; }       

    [Required]
    [Column("buildingNumber")]
    [MaxLength(255, ErrorMessage ="Building number must have 255 characters or less")]
    [Display(Name ="Building Number")]
    public string BuildingNumber { get; set; }      

    [Required]
    [Column("streetName")]
    [MaxLength(255, ErrorMessage ="Street name must have 255 characters or less")]
    [Display(Name ="Street Name")]
    public string StreetName { get; set; }        

    [Required]
    [Column("suburb")]
    [MaxLength(255, ErrorMessage ="Suburb must have 255 characters or less")]
    public string Suburb { get; set; }      

    [Required]
    [Column("state")]
    public string State { get; set; }        

    [Column("postCode")]
    [Display(Name ="Postcode")]
    public int PostCode { get; set; }

    public Customer Customer { get; set; }

}

谁能告诉我这里的问题是什么？感谢您对此的帮助

编辑：下面是 class 图

Answer 1

Select 是集合的 Linq 表达式。客户是一个单一的实体。您需要对多个级别使用 Include 来预先加载它们：

return context.Invoices
    .Include(p => p.PurchaseItems)
    .Include(c => c.Customer.CustomerAddress)
    .ToList();

当面对集合下方的引用时，您可以按名称预先加载它们。例如，如果 PurchaseItems 有一个产品：

return context.Invoices
    .Include(p => p.PurchaseItems)
    .Include("PurchaseItems.Product") // Loads product under each Purchase Item
    .Include(c => c.Customer.CustomerAddress)
    .ToList();

我相信这也可以使用 Select:

来完成

    .Include(p => p.PurchaseItems.Select(pi => pi.Product))

它适用于 PurchaseItems，因为它是一个集合，而 Customer 是一个单独的引用。

Select 在 EF6 中加载相关数据不起作用时包含在里面

Select inside Include When Loading Related Data in EF6 Is Not Working

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