实体框架单向导航

Question

I have two tables which store parts (FinishedGoods and OePart). It is guaranteed that no FinishedGoods and OePart record will have the same Id value.

Parts (OE or FinishedGoods) can have one or more Images (see database schema at bottom).

PartImageLink.PartId might refer to a FinishedGoods.Id, or it might refer to OePart.Id.

In Entity Framework (2.1.6) is it possible to have a navigation property from my C# entity for FinishedGoods and OePart to PartImageLink, but not have the reverse? Ideally I should be able save a FinishedGoods graph (including child PartImageLink and Image objects) and have it save all children. Is this even possible?

 CREATE TABLE FinishedGoods (
    Id INT PRIMARY KEY -- unique across all types of parts
 )

 CREATE TABLE OePart (
    Id INT PRIMARY KEY -- unique across all types of parts
 )

 CREATE TABLE PartImageLink (
    Id INT IDENTITY(1,1) PRIMARY KEY,
    PartId int not null, -- a FinishedGoods.Id OR an OePart.Id
    ImageId int not null
 )

 CREATE TABLE Image (
    id INT IDENTITY(1,1) PRIMARY KEY
 )

If PartImageLink stores a FinishedGoods.Id in column PartId, then it has no relationship to an OePart. But if PartImageLink stores an OePart.Id in column PartId, then it has no relationship to a FinishedGoods.

Answer 1

I think custom joins should work fine for you. I've prepared full example, the only thing is that I use in-memory storage instead of SQL. But it will work the same. Specific two functions answer your questions

IQueryable<PartImageLinkWithFinishedGoods> GetImageLinkWithFinishedGoods(AppDbContext db, int id)

and

IQueryable<PartImageLinkWithoePart> GetImageLinkWithoeParts(AppDbContext db, int id)

Note: static methods are not the best way you can query your db, but it should work as an example for your services

using Microsoft.EntityFrameworkCore;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;

namespace ConsoleApp22
{
    // The same models as in the example
    public class FinishedGoods
    {
        [Key]
        public int Id { get; set; }

        [NotMapped]
        public List<PartImageLink> PartImageLinks { get; set; } 
    }

    public class oePart
    {
        [Key]
        public int Id { get; set; }
    }

    public class PartImageLink
    {
        [Key]
        public int Id { get; set; }

        public int PartId { get; set; }
    }

    class AppDbContext : DbContext
    {
        public DbSet<FinishedGoods> FinishedGoods { get; set; }
        public DbSet<oePart> oeParts { get; set; }
        public DbSet<PartImageLink> PartImageLinks { get; set; }

        public AppDbContext(DbContextOptions options) : base(options)
        {
        }

        public override int SaveChanges()
        {
            foreach (var entry in ChangeTracker.Entries().ToList())
            {
                if (entry.Entity.GetType() == typeof(FinishedGoods))
                {
                    var finishedGoods = (FinishedGoods)entry.Entity;

                    if (finishedGoods.PartImageLinks != null)
                    {
                        foreach (var finishedGoodsPartLinks in finishedGoods.PartImageLinks)
                        {
                            Entry(finishedGoodsPartLinks).State = EntityState.Added;
                        }
                    }
                }
            }

            return base.SaveChanges();
        }
    }

    // Custom models to wrap query objects
    class PartImageLinkWithFinishedGoods
    {
        public FinishedGoods FinishedGoods { get; set; }

        public PartImageLink PartImageLink { get; set; }
    }

    class PartImageLinkWithoePart
    {
        public oePart oePart { get; set; }

        public PartImageLink PartImageLink { get; set; }
    }

    class Program
    {
        // Seed data
        private static void AddSomeData(AppDbContext db)
        {

            db.FinishedGoods.Add(new FinishedGoods()
            {
                Id = 1,
            });

            db.oeParts.Add(new oePart()
            {
                Id = 2,
            });

            db.PartImageLinks.Add(new PartImageLink()
            {
                Id = 1,
                PartId = 1,
            });

            db.PartImageLinks.Add(new PartImageLink()
            {
                Id = 2,
                PartId = 2,
            });

            db.FinishedGoods.Add(new FinishedGoods()
            {
                Id = 3,
                PartImageLinks = new List<PartImageLink>()
                {
                    new PartImageLink()
                    {
                        Id = 4,
                        PartId = 3
                    }
                }
            });

            db.SaveChanges();
        }

        // Query your main table and join whatever you expect on PartId field
        static IQueryable<PartImageLinkWithFinishedGoods> GetImageLinkWithFinishedGoods(AppDbContext db, int id)
        {
            return db.PartImageLinks.Where(x => x.Id == id)
                .Join(db.FinishedGoods,
                    x => x.PartId,
                    x => x.Id,
                    (x, y) => new PartImageLinkWithFinishedGoods() { PartImageLink = x, FinishedGoods = y });

        }

        static IQueryable<PartImageLinkWithoePart> GetImageLinkWithoeParts(AppDbContext db, int id)
        {
            return db.PartImageLinks.Where(x => x.Id == id)
                .Join(db.oeParts,
                    x => x.PartId,
                    x => x.Id,
                    (x, y) => new PartImageLinkWithoePart() { PartImageLink = x, oePart = y });

        }

        static void Main(string[] args)
        {
            var options = new DbContextOptionsBuilder().UseInMemoryDatabase("db").Options;
            var db = new AppDbContext(options);

            AddSomeData(db);

            var itemWithFinishedGoods = GetImageLinkWithFinishedGoods(db, 4).FirstOrDefault();
            var itemWithoePart = GetImageLinkWithoeParts(db, 2).FirstOrDefault();
        }

    }
}

Answer 2

What I ended up doing in my Link (junction) entity is making one property per type of part it could belong too.

public class PartImageLink (
    public int Id { get; set; }
    public int PartId { get; set; }
    public int ImageId { get; set; }

    public virtual OePart OePart { get; set; }
    public virtual FinishedGoods FinishedGoods { get; set; }

    public virtual Image Image { get; set; }
)

public class FinishedGoodsMap
{
    public FinishedGoodsMap(EntityTypeBuilder<FinishedGoods> entity)
    {
        entity.ToTable("FinishedGoods", schema: "dbo");
        entity.HasKey(e => e.Id);

        entity.HasMany(a => a.PartImageLinks).WithOne(b => b.FinishedGoods).HasForeignKey("PartId");
    }
}

public class OePartMap
{
    public OePartMap(EntityTypeBuilder<OePartMap> entity)
    {
        entity.ToTable("OePart", schema: "dbo");
        entity.HasKey(e => e.Id);

        entity.HasMany(a => a.PartImageLinks).WithOne(b => b.OePart).HasForeignKey("PartId");
    }
}

So my link table ends up with one navigation property per entity it can be linked too, but it allows me to save a single part and images as a graph.