EF Core loading relationships when I don't want it to

Question

I have a service that pulls back entities using EagerLoading. For the most part this works, but I have recently found an issue. I have a field:

public class Field
{
    [Required] public int Id { get; set; }
    [Required, MaxLength(100)] public string CategoryId { get; set; }
    [Required, MaxLength(100)] public string Name { get; set; }
    public FieldDataType DataType { get; set; }
    public bool IsSpecification { get; set; }

    public IList<FieldMap> FieldMaps { get; set; }
}

As you can see, it has a collection of FieldMaps associated with it. The FieldMap looks like this:

public class FieldMap
{
    public int Id { get; set; }
    public int FeedId { get; set; }
    public int FieldId { get; set; }
    [Required, MaxLength(100)] public string Path { get; set; }

    public Field Field { get; set; }
}

Which is mapped up in my DbContext like this:

modelBuilder.Entity<Field>().HasMany(m => m.FieldMaps).WithOne().HasForeignKey(m => m.FieldId);

// Unique constraints
modelBuilder.Entity<Field>().HasIndex(m => new { m.CategoryId, m.Name, m.IsSpecification }).IsUnique();
modelBuilder.Entity<FieldMap>().HasIndex(m => new { m.FeedId, m.Path }).IsUnique();

// Disable cascade delete
modelBuilder.Entity<FieldMap>().HasOne(m => m.Field).WithMany(m => m.FieldMaps).OnDelete(DeleteBehavior.Restrict);

The problem is, when I call the List method, it pulls back all items forever:

My list method is like this:

public IQueryable<T> List(params string[] includes)
{
    IQueryable<T> query = _dbEntitySet;

    return includes == null ? 
        query : 
        includes.Aggregate(query, (current, include) => current.Include(include));
}

And I invoke it like this:

[HttpGet("{id:int}/fields")]
[ProducesResponseType(typeof(List<Field>), StatusCodes.Status200OK)]
public IActionResult ListFieldMaps(int id)
{
    var feeds = _feedService.List();
    var feed = feeds.SingleOrDefault(m => m.Id.Equals(id));
    if (feed == null) return NotFound();

    var fieldMaps = _fieldMapService.List("Field");

    if (fieldMaps.Any(m => m.Field == null)) return BadRequest(Resources.NullFieldError);

    return Ok(fieldMaps.Where(m =>
        m.FeedId.Equals(id) &&
        m.Field.IsSpecification == (feed.Type == FeedType.Specification)).ToList());
}

As you can see, it should only load a list of FieldMaps with one Field, not the rest of the fieldmaps after that.

Can someone help me with this issue?

Answer 1

I found this article:

https://learn.microsoft.com/en-us/ef/core/querying/related-data#lazy-loading

and this issue:

https://github.com/aspnet/EntityFrameworkCore/issues/11564

and from both of them was able to add this:

services.AddMvc()
    .AddJsonOptions(options =>
        options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore);

Which caused my issue to be resolved. Now when I do a request, I get this response:

[
    {
        "Id": 1,
        "FeedId": 1,
        "FieldId": 10,
        "Path": "aw_product_id",
        "Field": {
            "Id": 10,
            "CategoryId": "cameras",
            "Name": "gtin",
            "DataType": 0,
            "IsSpecification": false,
            "FieldMaps": []
        }
    }
]