relations.cs

if (bodyText.InvariantContains(product.Name))
{
    if (relationService.AreRelated(doc, product, "product") == false)
    {
        relationService.Relate(doc, product, "product");
    }
}
else
{
    if (relationService.AreRelated(doc, product, "product") == true)
    {
        var type = relationService.GetRelationTypeByAlias("product");
        var relations = relationService.GetAllRelationsByRelationType(type.Id)
            .Where(x => x.ParentId == doc.Id && x.ChildId == product.Id);

        foreach (var relation in relations)
        {
            relationService.Delete(relation);
        }
    }
}