How to return object references in ASP.net core Web API - rest

Question

I dont understand why getAllAssemblies() return referenced objects where "getAssembly(int id)" does not.
Can you give a heads up on how to have referenced objects returned from both methods?
The type:
public class Assembly
{
public int Id { get; init; }
public string? Name { get; set; }
public List<Object>? ChildrenObjects { get; set; }
[Required]
public int ParrentObjectId { get; set; }
[JsonIgnore]
public Assembly? ParrentObject { get; set; }
}
The data:
modelBuilder.Entity<Assembly>().HasData(
new Assembly() { Id = 10, Name = "1" },
new Assembly() { Id = 11, Name = "1.1", ParrentObjectId = 10
});
GetAssembly(int id)
[HttpGet("{id}")]
public async Task<ActionResult> GetAssembly(int id)
{
return Ok(await _objectsContext.Assemblies.FindAsync(id));
}
returns:
{
"id": 10,
"name": "1",
"childrenObjects": null,
"parrentObjectId": 0
}
GetAllAssemblies()
public async Task<ActionResult> GetAllAssemblies()
{
return Ok(await _objectsContext.Assemblies.ToListAsync());
}
returns:
[
{
"id": 10,
"name": "1",
"childrenObjects": [
{
"id": 11,
"name": "1.1",
"childrenObjects": null,
"parrentObjectId": 10
}
],
"parrentObjectId": 0
},
{
"id": 11,
"name": "1.1",
"childrenObjects": null,
"parrentObjectId": 10
}
]