public static IIfPropertyElement <TEntity, TEntity> WhereEntity <TEntity>(this IIfPropertyElement <TEntity, TEntity> el)
 {
     el.Property = e => e;
     return(el);
 }
 //public static IIfPropertyElement<TEntity, TEntityProperty> WhereProperty<TEntity, TEntityProperty>(this IIfPropertyElement<TEntity, TEntityProperty> el, Func<TEntity, TEntityProperty> prop)
 public static IIfPropertyElement <TEntity, TEntityProperty> WhereProperty <TEntity, TEntityProperty>(this IIfPropertyElement <TEntity, TEntityProperty> el, Func <IConventionParams <TEntity>, IConventionParams <TEntityProperty> > prop)
 {
     el.Property = prop;
     return(el);
 }