树形菜单的存储设计

##关系型数据库设计 ###parent_id |id |name | parent_id| |---|-------|-----------| |1 |A |NULL | |2 |B |1 | |3 |C |1 | |4 |D |2 |

优缺点：

Pros: Easy to understand, fast to insert and move
Cons: Requires multiple queries to get whole subtrees

针对查询问题，可以应用缓存来解决

###left&right

id	name	parent_id	left	right
1	A	NULL	1	8
2	B	1	2	5
3	C	1	6	7
4	D	2	3	4

Pros: Lookup up entire subtrees with a single query (fast), intrinsic ordering of children
Cons: Slow to insert and move, due to many modifications of existing records

针对修改问题，由于菜单读多写少，可以接受

###记录path

id	name	parent_id	path
1	A	NULL	1-
2	B	1	1-2-
3	C	1	1-2-
4	D	2	1-2-4-

查询快修改麻烦

##文档型数据库 ###直接存json


{

  "name": "A",

  "children": [

    {"name": "B", "children": [{"name": "D"}]},

    {"name": "C"}

  ]

}

Pros: Native tree-like data structure, intrinsic ordering of children
Cons: Could get ugly with larger and more complex documents, concurrency is limited

增加version，进行版本/乐观锁并发控制

###使用parent_id


{"_id": "A"}

{"_id": "B", "parent_id": "A"}

{"_id": "C", "parent_id": "A"}

{"_id": "D", "parent_id": "B"}

Pros: Simple to understand, easy to find parent
Cons: Needs good view or index to find child documents, no intrinsic ordering of children

###使用children

{"_id": "A", "children": ["B", "C"]}
{"_id": "B", "children": ["D"]}
{"_id": "C"}
{"_id": "D"}

Pros: Simple to understand, easy to find children, intrinsic ordering of children Cons: Needs good view or index to find parent document

###索引法

{

  "leaf": "A",

  "children": [

    {"leaf": "B", "children": [{"leaf": "D"}] },

    {"leaf": "C"}

  ]

}

{"_id": "A", ...}

{"_id": "B", ...}

{"_id": "C", ...}

{"_id": "D", ...}

Pros: Two lookups to find any node, native tree data structure, data separate from tree, intrinsic ordering
Cons: Traversing from one node to another requires referring back to the tree data structure (maybe this is not a bad thing — it can be cached), concurrency is limited

##存储层级以及路径 Storing the node path along with hierarchy level int the document.

{ele: "a", path: "/a" , lvl:1} 
{ele: "b", path: "/a/b", lvl:2} 
{ele: "c", path: "/a/b/c", lvl:3}

Pros : Easy to fetch a subtree of a given node. Traversing up a tree is not that difficult. Getting all parent nodes of c:db..find({"path" : {"$in" : ["/a", "/a/b"] } }).
Cons : If hierarchical changes are frequent, then path update is needed but still easier than other models.

##doc

来源：oschina

链接：https://my.oschina.net/u/2922256/blog/790884

标签

design