code: function Projection(database, input)
  {
    this.database = database;
    this.input = input;
    this.projections = {};
  
    for (var i = 0; i < input.length; i++)
    {
      this.addProjection( input[ i ] );
    }
  }
docs: field relation.field relations[pluckValue] relations?savedWhere[pluckValue] relations{pluckKey: pluckValue} relation(subprojection) relations(subprojection) relations?savedWhere(subprojection) expression|filter expression?savedWhere alias:expression expression#resolve relations@sum=field