如何在同一个表上创建数据或实体关系并在第一个连接表上连接另一个表？

Question

I'm having a problem building data or entity relationships with the same table and joining another table to the first inner joined table.

I want to get the query result this way:

SELECT [n].[ISCInstanceId], [n].[NavPointId], [n].[ParentNPId], [n].[DataPointId], [n].[NodeOrder], [n].[RefNumber], [n].[TreeTitle], [n].[IsArchived], [n].[IsInNavbar], [i].[Name]
  FROM [NavPoints] AS [n]
  INNER JOIN [NavPoints] AS [n0] ON [n].[ParentNPId] = [n0].[NavPointId]
  INNER JOIN [ISCInstances] AS [i] ON [n0].[ISCInstanceId] = [i].[ISCInstanceId]
  WHERE (([n].[IsArchived] = CAST(0 AS bit)) AND ([n].[IsInNavbar] = CAST(1 AS bit))) AND ([n0].[ISCInstanceId] = @__IscinstanceId_0)
  ORDER BY [n].[ParentNPId], [n].[NodeOrder]

but I'm getting this:

SELECT [n].[ISCInstanceId], [n].[NavPointId], [n].[ParentNPId], [n].[DataPointId], [n].[NodeOrder], [n].[RefNumber], [n].[TreeTitle], [n].[IsArchived], [n].[IsInNavbar], [i].[Name]
  FROM [NavPoints] AS [n]
  INNER JOIN [NavPoints] AS [n0] ON [n].[ParentNPId] = [n0].[NavPointId]
  INNER JOIN [ISCInstances] AS [i] ON [n].[ISCInstanceId] = [i].[ISCInstanceId]
  WHERE (([n].[IsArchived] = CAST(0 AS bit)) AND ([n].[IsInNavbar] = CAST(1 AS bit))) AND ([n0].[ISCInstanceId] = @__IscinstanceId_0)
  ORDER BY [n].[ParentNPId], [n].[NodeOrder]

The problem is that section or line INNER JOIN [ISCInstances] AS [i] ON [n].[ISCInstanceId] = [i].[ISCInstanceId] witch is the query I'm getting is not joining to the first inner joined table, I want it to be like this INNER JOIN [ISCInstances] AS [i] ON [n0].[ISCInstanceId] = [i].[ISCInstanceId]

DB Context

modelBuilder.Entity<NavPoint>(entity =>
{
    ...
    entity.HasOne(d => d.Iscinstances)
        .WithMany(p => p.NavPoints)
        .HasForeignKey(d => d.IscinstanceId)
        .OnDelete(DeleteBehavior.ClientSetNull)
        .HasConstraintName("FK_NavPoints_Iscinstances");

    entity.HasOne(d => d.NavPointsParent)
        .WithMany(p => p.NavPoints)
        .HasForeignKey(d => d.ParentNpid)
        .OnDelete(DeleteBehavior.ClientSetNull)
        .HasConstraintName("FK_NavPoints_NavPoints");
});

Class Model

// <auto-generated> This file has been auto generated by EF Core Power Tools. </auto-generated>
#nullable disable
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations.Schema;

namespace Odysseus_API.Models
{
    public partial class NavPoint
    {
        public NavPoint()
        {
            NavPoints = new HashSet<NavPoint>();
        }
        [key]
        public int NavPointId { get; set; }
        public int ParentNpid { get; set; }
        ...
        [ForeignKey("ParentNpid")]
        public virtual NavPoint NavPointsParent { get; set; }
        public virtual Iscinstance Iscinstances { get; set; }
        [ForeignKey("NavPointId")]
        public virtual ICollection<NavPoint> NavPoints { get; set; }
    }
}

Controller

[HttpGet]
public async Task<ActionResult<NavPoint>> GetNavPoint(int IscinstanceId)
{
    if (_context.Users == null)
    {
        return NotFound();
    }

    var navpoint = await _context.NavPoints
               .Where(c => c.IsArchived == false  && c.IsInNavbar == true && c.NavPointsParent.IscinstanceId == IscinstanceId)
               .Include(c => c.NavPointsParent).Include(c => c.Iscinstances)
               .OrderBy(c => c.ParentNpid).ThenBy(c => c.NodeOrder)
               .Select(c => new NavPoint
               {
                   ...
               })
               .ToListAsync();

    if (navpoint == null)
    {
        return NotFound();
    }

    return Ok(navpoint);
}

Answer 1

Basically what you have is:

var navpoint = await _context.NavPoints
    .Include(c => c.NavPointsParent)
    .Include(c => c.Iscinstances)

Include always applies to the root of the query, so you include the Iscinstances of _context.NavPoints . This would have the same effect:

var navpoint = await _context.NavPoints
    .Include(c => c.Iscinstances)
    .Include(c => c.NavPointsParent)

To Include the Iscinstances of NavPointsParent , use:

var navpoint = await _context.NavPoints
    .Include(c => c.NavPointsParent)
        .ThenInclude(c => c.Iscinstances)

ThenInclude expands a previous Include .

After your comments: the point here is that you need the navigation property c.NavPointsParent.Iscinstance , even when not using Include .