I got this entity for friendlists:

public class Friendship : IEntity
{
    /// <summary>
    ///     Gets or sets the usr a.
    /// </summary>
    /// <value>
    ///     The usr a.
    /// </value>
    public virtual Users UsrA { get; set; }

    /// <summary>
    ///     Gets or sets the usr b.
    /// </summary>
    /// <value>
    ///     The usr b.
    /// </value>
    public virtual Users UsrB { get; set; }


    /// <summary>
    ///     Gets or sets the identifier.
    /// </summary>
    /// <value>
    ///     The identifier.
    /// </value>
    public virtual long Id { get; set; }
}

With the mapping:

public class FriendshipOverrides : IAutoMappingOverride<Friendship>
{
    public void Override(AutoMapping<Friendship> mapping)
    {
        mapping.References(x => x.UsrA, "UsrAId").Cascade.None().Index("FriendshipUsrAIdx");
        mapping.References(x => x.UsrB, "UsrBId").Cascade.None().Index("FriendshipUsrBIdx");
        mapping.HasMany(x => x.Feeds).Cascade.None();
    }
}

Each user can has a privacy config mapped referenced by the user entity.

So what I try is to filter out users which profile is not public.

     var friendListQuery = this._FriendshipRepository.Query()!.Select(x => new
     {
         u = x.UsrA.Id == userId ? x.UsrB : x.UsrA,
         f = x,
         priv = (x.UsrA.Id == userId ? x.UsrB : x.UsrA).PrivacyConfig 
     })
         .Where(x => x.f.UsrA.Id == userId || x.f.UsrB.Id == userId);

Everything works as expected as long I am not accessing a child entity of UsrA or UsrB (in this case PrivacyConfig).

It doesnt matter where I access it (Select, Where, OrderBy etc) Results always in the error: Nhibernate: Cannot visit a constant without a constant to parameter map Since the mapping of the UserObject is quiet long here a snapshot:

 mapping.References(x => x.PrivacyConfig).Cascade.All();

and on privacy config override:

public class UserPrivacyDataOverrides : IAutoMappingOverride<UserPrivacyData>
{
    public void Override(AutoMapping<UserPrivacyData> mapping)
    {
        mapping.HasOne(x => x.User).Cascade.None();
    }
}

Couldnt find any solution online when searching for the error.