在數(shù)據(jù)庫(kù)設(shè)計(jì)中，通常使用ID/PID這樣的模式表示上下級(jí)關(guān)系，最常見的就是category表的設(shè)計(jì)，比如
CREATE TABLE IF NOT EXISTS `item`.`item_category` (
? `item_category_id` BIGINT UNSIGNED NOT NULL,
? `store_id` BIGINT UNSIGNED NOT NULL COMMENT '所屬店鋪ID',
? `category_name` VARCHAR(45) NOT NULL COMMENT '分類名稱',
? `parent_id` BIGINT UNSIGNED NOT NULL DEFAULT 0 COMMENT '父級(jí)分類ID',
? `create_time` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
? `create_user_id` BIGINT UNSIGNED NOT NULL,
? `last_modify_time` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
? `last_modify_user_id` BIGINT UNSIGNED NOT NULL,
? `is_deleted` BIGINT UNSIGNED NOT NULL DEFAULT 0,
? PRIMARY KEY (`item_category_id`)
)
COMMENT = '商品分類'
使用parent_id表示上級(jí)分類，這種表示上下級(jí)的方式在數(shù)據(jù)庫(kù)設(shè)計(jì)中很通用，因此，是否有種方式將這種結(jié)構(gòu)快速的生成樹形結(jié)構(gòu)呢？
用于將具有ID/PID這種結(jié)構(gòu)的數(shù)據(jù)生成Tree，比如保存省市縣的數(shù)據(jù)
IntIdPidEntry china = new IntIdPidEntry(1, rootId, "中國(guó)");
IntIdPidEntry hunan_province = new IntIdPidEntry(2, 1, "湖南省");
IntIdPidEntry zhangjj = new IntIdPidEntry(3, 2, "張家界市");
IntIdPidEntry changsha = new IntIdPidEntry(4, 2, "長(zhǎng)沙市");
IntIdPidEntry sangzhi = new IntIdPidEntry(5, 3, "桑植縣");
IntIdPidEntry guangdong_province = new IntIdPidEntry(7, 1, "廣東省");
IntIdPidEntry guangzhou = new IntIdPidEntry(8, 7, "廣州市");
IntIdPidEntry tianhe = new IntIdPidEntry(12, 8, "天河區(qū)");
IntIdPidEntry dongguan = new IntIdPidEntry(9, 7, "東莞市");
IntIdPidEntry hubei_province = new IntIdPidEntry(10, 1, "湖北省");
IntIdPidEntry yunan_province = new IntIdPidEntry(11, 1, "云南省");
我們只需要將這些數(shù)據(jù)使用IdPidEntryTreeBuilder add到給定的Tree中即可
List<IntIdPidEntry> elements = getElements();? // 上面的數(shù)據(jù)列表
Tree<Integer, MyTreeElement> tree = new MappedTree<>();
IdPidEntryTreeBuilder<Integer, IntIdPidEntry, MyTreeElement> builder = new IdPidEntryTreeBuilder<>();
builder.add(tree, elements, mapper); // 將數(shù)據(jù)add到樹中即可生成樹形結(jié)構(gòu)
