Entity Framework 的 Eager Loading 仅填充最后一条记录

Question

I have a ASP.NET Core 3.1 Web API with the following database context:

namespace Api.Database.EF
{
    using System;
    using Microsoft.EntityFrameworkCore;
    
    using Api.Database.EF.Models;

    public class ApiDbContext : DbContext
    {
        private readonly string connectionString;
        private readonly DbContextOptions<ApiDbContext> options;

        public ApiDbContext(string connectionString)
        {
            if (string.IsNullOrEmpty(connectionString))
            {
                throw new ArgumentNullException(
                    nameof(connectionString),
                    "Connection string cannot be null or empty.");
            }

            this.connectionString = connectionString;
        }

        public ApiDbContext(DbContextOptions<ApiDbContext> options)
        {
            this.options = options;
        }

        public DbSet<SearchFilter> SearchFilter { get; set; }

        public DbSet<SearchFilterData> SearchFilterData { get; set; }

        public DbSet<FilterStatus> FilterStatus { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<SearchFilterData>()
                .HasOne<SearchFilter>(d => d.SearchFilter)
                .WithMany(f => f.SearchFilterData)
                .HasForeignKey(f => f.SearchFilterId);

            modelBuilder.Entity<SearchFilterData>()
                .HasOne<FilterStatus>(x => x.Status)
                .WithOne(x => x.SearchFiltersData)
                .HasForeignKey<SearchFilterData>(x => x.StatusId);

            modelBuilder.Entity<SearchFilterData>()
                .Property(p => p.CreatedAt)
                .HasDefaultValueSql("CURRENT_TIMESTAMP()");
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!string.IsNullOrEmpty(this.connectionString))
            {
                optionsBuilder.UseMySQL(this.connectionString);
            }
        }
    }
}

And the following 3 models:

namespace Api.Database.EF.Models
{
    using System.ComponentModel.DataAnnotations;
    using System.ComponentModel.DataAnnotations.Schema;
    using System.Collections.Generic;
    using Newtonsoft.Json;
    
    [Table("search_filter_status")]
    public class FilterStatus
    {
        [Key]
        [Column("id")]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        [Column("name")]
        public string Name { get; set; }

        [JsonIgnore]
        public virtual SearchFilterData SearchFiltersData { get; set; }
    }
}

#nullable enable
namespace Api.Database.EF.Models
{
    using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations;
    using System.ComponentModel.DataAnnotations.Schema;
    using Newtonsoft.Json;

    [Table("search_filter")]
    public class SearchFilter
    {
        [Key]
        [Column("id")]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        [Required]
        [Column("guid")]
        public string Guid { get; set; }

        [Required]
        [Column("user")]
        public string User { get; set; }

        [Column("name")]
        public string? Name { get; set; }

        [Column("description")]
        public string? Description { get; set; }
        
        [JsonProperty("data")]
        public virtual List<SearchFilterData> SearchFilterData { get; set; }
    }
}

namespace Api.Database.EF.Models
{
    using System;
    using System.ComponentModel.DataAnnotations;
    using System.ComponentModel.DataAnnotations.Schema;
    using Newtonsoft.Json;

    [Table("search_filter_data")]
    public class SearchFilterData
    {
        [Key]
        [Column("id")]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        [Column("search_filter_id")]
        public int SearchFilterId { get; set; }

        [Column("created")]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public DateTimeOffset CreatedAt { get; set; }

        [Column("status_id")]
        public int StatusId { get; set; }

        [Column("data")]
        public string FilterData { get; set; }

        public virtual FilterStatus Status { get; set; }
        
        [JsonIgnore]
        public virtual SearchFilter SearchFilter { get; set; }
    }
}

This is how I try to use it:

public List<SearchFilterData> GetFiltersForUser(string username)
{
    return this.apiDbContext
        .SearchFilterData
        .Where(x => x.SearchFilter.User == username)
        .Include(x => x.Status)
        .ToList();
}

The issue I'm facing here is that only the last item has a value it's Status property. Here is a sample response:

[
    {
        "Id": 1,
        "SearchFilterId": 1,
        "CreatedAt": "2022-07-14T13:16:43+03:00",
        "StatusId": 1,
        "FilterData": "{}",
        "Status": null
    },
    {
        "Id": 2,
        "SearchFilterId": 1,
        "CreatedAt": "2022-07-14T14:04:33+03:00",
        "StatusId": 1,
        "FilterData": "some_data",
        "Status": null
    },
    {
        "Id": 3,
        "SearchFilterId": 1,
        "CreatedAt": "2022-07-14T14:05:17+03:00",
        "StatusId": 1,
        "FilterData": "some_other_data",
        "Status": {
            "Id": 1,
            "Name": "ACTIVE"
        }
    }
]

No matter how many items I add, it's always the last one only that has the Status object inside it. Any suggestions where the issue might come from?

Answer 1

You have duplicate StatusId values in SearchFilterData , which is against the configured one-to-one relationship (one-to-one means the StatusId is unique in the referencing side as well, ie in SearchFilterData ), hence the results you are getting from EF Core.

The database tables and the data itself imply that the relationship between FilterStatus and SearchFilterData is one-to- many , like the other one. So in order to fix the problem, you need to fix your model and fluent configuration, because EF Core behaviors heavily rely on that, and not what is really in the database, so these must be in sync.

So, in FilterStatus

[JsonIgnore]
public virtual SearchFilterData SearchFiltersData { get; set; }

becomes

[JsonIgnore]
public virtual ICollection<SearchFilterData> SearchFiltersData { get; set; }

or List or any IEnumerable<SearchFilterData> type.

And the fluent configuration for the relationship is changed to (or just removed since the reference navigation and FK property names match the EF Core conventions):

modelBuilder.Entity<SearchFilterData>()
    .HasOne(x => x.Status)
    .WithMany(x => x.SearchFiltersData) // <--
    .HasForeignKey(x => x.StatusId);

---

PS Note that if you have used EF Core migration to create database tables from the model, it would have created unique constraint on StatusId column, so you won't be able to input duplicate values and exhibit the issue in question.