Entity Framework Core [NotMapped] property helper to retrieve single entity from a collection

I want to be able to achieve something like:

public class EntityWithCollection
{
    public int Id { get; set; }
    [NotMapped]
    public DependentEntity 
    {
        get 
        {
            return Dependencies?.SingleOrDefault(d => d.IsActive);
        }
    }
    [JsonIgnore]
    [InverseProperty("Parent")]
    public ICollection<DependentEntity> Dependencies { get; set; }
}

public class DependentEntity
{
    public int Id { get; set; }
    
    public string Name { get; set; }
    
    [JsonIgnore]
    public bool IsActive { get; set; }

    public int ParentId { get; set; }
    [ForeignKey("ParentId")]
    public EntityWithCollection Parent { get; set; }
}

But without making circular reference, i.e. additional column for DependentEntityId, this works for GET but doesn't work for POST,PUT anything that writes

So from my Web API I can POST JSON like:

POST /entitiesWithCollection 
{"dependentEntity": { "name": "Chuck Norris"
    }
}

there can be only one IsActive=1 row for a given child. For that I have UNIQUE constraint:

builder.Entity<DependentEntity>().HasIndex(e => e.ParentId).HasFilter("IsActive=1");

How can I make this work so I can UPDATE and INSERT using [NotMapped] property?