无法弄清楚 Linq 连接

Question

在 LinqPad 中，我有这个工作，底层 SQL 查询是我想要的：

from userProcesses in UserProcesses
join formProcesses in FormProcesses 
   on userProcesses.ProcessID equals formProcesses.Process_ProcessID
join forms in Forms 
    on formProcesses.Form_FormID equals forms.FormID
join userForms in UserForms
    on new {userProcesses.UserProcessID, forms.FormID} equals 
       new {userForms.UserProcessID, userForms.FormID} into combined
from c in combined.DefaultIfEmpty()
select new
{
    UserFormID = c == null ? (int?) null : c.UserFormID,
    FormID = forms.FormID,
    Name = forms.Name
}

问题是，在我的实际代码中，FormProcesses table 本身并没有暴露，而是一个导航属性。我一直在为如何在我的软件中编写此查询而苦苦挣扎。

这是我的模型的骨架视图，因此您可以看到导航属性：

public class UserProcess : BaseModel
    {
        [Key]
        public int UserProcessID { get; set; }

        [Required]
        [ForeignKey("Process")]
        public int ProcessID { get; set; }

        public Process Process { get; set; }

        public virtual ICollection<UserForm> UserForms { get; set; }
    }

 public class Form : Common.BaseModel
    {
        [Key]
        public int FormID { get; set; }       

        public virtual ICollection<Process> Processes { get; set; }
    }

public class UserForm : Common.BaseModel
    {
        [Key]
        public int UserFormID { get; set; }

        [Required]
        [ForeignKey("UserProcess")]
        public int UserProcessID { get; set; }

        public UserProcess UserProcess { get; set; }

        [Required]
        [ForeignKey("Form")]
        public int FormID { get; set; }

        public Form Form { get; set; }
    }

public class Process : Common.BaseModel
    {
        [Key]
        public int ProcessID { get; set; }

        public virtual ICollection<Form> Forms { get; set; }
    }

我做错了什么 - 我怎样才能让它工作？

Answer 1

您可以通过导航属性将所有显式连接替换为 "navigating"。

例如，以下连接

join formProcesses in FormProcesses
    on userProcesses.ProcessID equals formProcesses.Process_ProcessID
join forms in Forms
    on formProcesses.Form_FormID equals forms.FormID

成为：

from forms in userProcesses.Process.Forms

应该可以解决问题。

可选地，LINQ to Entities 编写以下连接的方式：

join userForms in UserForms
    on new { userProcesses.UserProcessID, forms.FormID } equals
       new { userForms.UserProcessID, userForms.FormID } into combined

是：

let combined = from userForms in userProcesses.UserForms
               where userForms.FormID == forms.FormID
               select userForms

无法弄清楚 Linq 连接

Can't figure out a Linq join

linq

linq-to-entities

entity-framework