transmet/categories/categories.go

package categories

import (
	"database/sql"
	"errors"
	"fmt"
	_ "github.com/lib/pq"
	"strings"
)

type Category struct {
	Id       int
	Name     string
	Parent   sql.NullInt64
	Children []*Category
}

var CategoriesTree []*Category
var CategoriesFlat map[int]*Category

// Cavet: slight cheat. All parents must have Category_id < their children.
func LoadCategories(db *sql.DB) {
	CategoriesTree = []*Category{}
	CategoriesFlat = make(map[int]*Category)

	rows, err := db.Query("select categories.id, categories.name, categories.parent_id from categories order by coalesce(parent_id, id), parent_id is not null")
	if err != nil {
		fmt.Println("DB Error loading Categories:", err)
		return
	}
	defer rows.Close()

	for rows.Next() {
		category := &Category{Children: []*Category{}}

		err = rows.Scan(&category.Id, &category.Name, &category.Parent)
		if err != nil {
			fmt.Println("Categories DB Error: ", err)
		}

		CategoriesFlat[category.Id] = category

		if category.Parent.Valid {
			pid := int(category.Parent.Int64)
			CategoriesFlat[pid].Children = append(CategoriesFlat[pid].Children, category)
		} else {
			CategoriesTree = append(CategoriesTree, category)
		}
	}
}

func Add(db *sql.DB, name string, parent int) error {
	var err error
	if parent < 0 {
		_, err = db.Exec("INSERT INTO categories (name) VALUES ($1)", name)
	} else {
		_, err = db.Exec("INSERT INTO categories (name, parent_id) VALUES ($1, $2)", name, parent)
	}
	if err != nil {
		fmt.Println("Categories DB Error Add(): ", err)
	}
	return err
}

// Get parent id
//  Set parent of children to parent
//  set category of news to parent
//  finallly delete
func Delete(db *sql.DB, id int) error {
	rows, err := db.Query("SELECT parent_id FROM categories WHERE id=$1", id)
	if err != nil {
		fmt.Println("Categories DB Error loading category parent id: ", err)
		return err
	}

	if !rows.Next() {
		fmt.Println("Categories DB Error loading category parent id: no category")
		return errors.New("No category")
	}
	var parent_id sql.NullInt64
	err = rows.Scan(&parent_id)

	_, err = db.Exec("UPDATE categories SET parent_id =$2 WHERE parent_id=$1", id, parent_id)
	if err != nil {
		fmt.Println("Categories DB error changing child parent: ", err)
		return err
	}

	_, err = db.Exec("UPDATE news SET category_id =$2 WHERE category_id=$1", id, parent_id)
	if err != nil {
		fmt.Println("Categories DB error changing category of news: ", err)
		return err
	}

	_, err = db.Exec("DELETE FROM categories WHERE id=$1", id)
	if err != nil {
		fmt.Println("Categories DB Error Delete(): ", err)
	}
	return err
}

func (category *Category) ChangeParent(db *sql.DB, parent *Category) error {
	var err error
	if parent == nil {
		_, err = db.Exec("UPDATE categories SET parent_id = NULL WHERE id = $1", category.Id)
	} else {
		_, err = db.Exec("UPDATE categories SET parent_id = $2 WHERE id = $1", category.Id, parent.Id)
	}

	if err != nil {
		fmt.Println("Categories DB Error: ", err)
	}
	return err
}

// get the number of parents a category has
func (category *Category) Depth() int {
	depth := 0
	current := category
	for current.Parent.Valid {
		current = CategoriesFlat[int(current.Parent.Int64)]
		depth++
	}
	return depth
}

// Helper function for templates (add form select list)
func (category *Category) ToString() string {
	return strings.Repeat("- ", category.Depth()) + category.Name
}