relay pagination.go

func (r *queryResolver) FindUsers(ctx context.Context, search *string, first *int, last *int, after *string, before *string) (*model.UserConnection, error) {
	var (
		nodes    []*model.User
		edges    []*model.UserEdge
		pageInfo model.PageInfo
	)
	query := r.DB.Model(&nodes)
	if search != nil {
		s := *search
		if len(s) > 0 {
			s = "%" + s + "%"
			query.WhereGroup(func(q *orm.Query) (*orm.Query, error) {
				q = q.
					WhereOr("first_name LIKE ?", s).
					WhereOr("last_name LIKE ?", s).
					WhereOr("email LIKE ?", s)
				return q, nil
			})
		}
	}
	if last != nil {
		query.Limit(*last + 1).Order("id ASC")
		pageInfo.HasNextPage = false
	}
	if first != nil {
		pageInfo.HasPreviousPage = false
		query.Limit(*first + 1).Order("id DESC")
	}
	if before != nil {
		if len(*before) > 0 {
			_, realId := unique.DecodeGlobalID(*before)
			query.Where("id < ?", realId)
		}
	}
	if after != nil {
		if len(*after) > 0 {
			_, realId := unique.DecodeGlobalID(*after)
			query.Where("id > ?", realId)
		}
	}
	count, err := query.SelectAndCount()
	if err != nil {
		return nil, err
	}
	if last != nil {
		if count >= *last+1 {
			pageInfo.HasPreviousPage = true
		}
	}
	if first != nil {
		if count >= *first+1 {
			pageInfo.HasNextPage = true
		}
	}
	if first != nil || last != nil {
		shouldMinusOne := false
		if first != nil {
			if count >= *first+1 {
				shouldMinusOne = true
			}
		}
		if last != nil {
			if count >= *last+1 {
				shouldMinusOne = true
			}
		}
		if shouldMinusOne {
			nodes = nodes[0:(len(nodes) - 1)]
		}
	}
	for index, node := range nodes {
		cursor := node.ToGlobalID()
		if index == 0 {
			pageInfo.StartCursor = &cursor
		}
		pageInfo.EndCursor = &cursor
		edges = append(edges, &model.UserEdge{
			Cursor: cursor,
			Node:   node,
		})
	}
	res := &model.UserConnection{
		Edges:    edges,
		Count:    count,
		PageInfo: &pageInfo,
	}
	return res, nil
}