Library for implementing Modified Preorder Tree Traversal with your SQLAlchemy Models and working with trees of Model instances, like django-mptt. Docs http://sqlalchemy-mptt.readthedocs.io/
The nested set model is a particular technique for representing nested sets (also known as trees or hierarchies) in relational databases.
Install from github:
pip install git+http://github.com/uralbash/sqlalchemy_mptt.gitPyPi:
pip install sqlalchemy_mpttSource:
pip install -e .Add mixin to model
from sqlalchemy import Column, Integer, Boolean
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy_mptt.mixins import BaseNestedSets
Base = declarative_base()
class Tree(Base, BaseNestedSets):
__tablename__ = "tree"
id = Column(Integer, primary_key=True)
visible = Column(Boolean)
def __repr__(self):
return "<Node (%s)>" % self.idNow you can add, move and delete obj!
node = Tree(parent_id=6)
session.add(node)level Nested sets example
1 1(1)22
_______________|___________________
| | |
2 2(2)5 6(4)11 12(7)21
| ^ ^
3 3(3)4 7(5)8 9(6)10 13(8)16 17(10)20
| |
4 14(9)15 18(11)19
level Insert node with parent_id == 6
1 1(1)24
_______________|_________________
| | |
2 2(2)5 6(4)13 14(7)23
| ____|____ ___|____
| | | | |
3 3(3)4 7(5)8 9(6)12 15(8)18 19(10)22
| | |
4 10(23)11 16(9)17 20(11)21
node = session.query(Tree).filter(Tree.id == 4).one()
session.delete(node)level Nested sets example
1 1(1)22
_______________|___________________
| | |
2 2(2)5 6(4)11 12(7)21
| ^ ^
3 3(3)4 7(5)8 9(6)10 13(8)16 17(10)20
| |
4 14(9)15 18(11)19
level Delete node == 4
1 1(1)16
_______________|_____
| |
2 2(2)5 6(7)15
| ^
3 3(3)4 7(8)10 11(10)14
| |
4 8(9)9 12(11)13
node = session.query(Tree).filter(Tree.id == 8).one()
node.parent_id = 5
session.add(node)level Nested sets example
1 1(1)22
_______________|___________________
| | |
2 2(2)5 6(4)11 12(7)21
| ^ ^
3 3(3)4 7(5)8 9(6)10 13(8)16 17(10)20
| |
4 14(9)15 18(11)19
level Move 8 - > 5
1 1(1)22
_______________|__________________
| | |
2 2(2)5 6(4)15 16(7)21
| ^ |
3 3(3)4 7(5)12 13(6)14 17(10)20
| |
4 8(8)11 18(11)19
|
5 9(9)10
Nested sets multitree
Move inside
node = session.query(Tree).filter(Tree.id == 4).one()
node.move_inside("15") 4 -> 15
level Nested sets tree1
1 1(1)16
_______________|_____________________
| |
2 2(2)5 6(7)15
| ^
3 3(3)4 7(8)10 11(10)14
| |
4 8(9)9 12(11)13
level Nested sets tree2
1 1(12)28
________________|_______________________
| | |
2 2(13)5 6(15)17 18(18)27
| ^ ^
3 3(14)4 7(4)12 13(16)14 15(17)16 19(19)22 23(21)26
^ | |
4 8(5)9 10(6)11 20(20)21 24(22)25
Move after
node = session.query(Tree).filter(Tree.id == 8).one()
node.move_after("5")level Nested sets example
1 1(1)22
_______________|___________________
| | |
2 2(2)5 6(4)11 12(7)21
| ^ ^
3 3(3)4 7(5)8 9(6)10 13(8)16 17(10)20
| |
4 14(9)15 18(11)19
level Move 8 after 5
1 1(1)22
_______________|__________________
| | |
2 2(2)5 6(4)15 16(7)21
| ^ |
3 3(3)4 7(5)8 9(8)12 13(6)14 17(10)20
| |
4 10(9)11 18(11)19
Move to top level
node = session.query(Tree).filter(Tree.id == 15).one()
node.move_after("1")level tree_id = 1
1 1(1)22
_______________|___________________
| | |
2 2(2)5 6(4)11 12(7)21
| ^ ^
3 3(3)4 7(5)8 9(6)10 13(8)16 17(10)20
| |
4 14(9)15 18(11)19
level tree_id = 2
1 1(15)6
^
2 2(16)3 4(17)5
level tree_id = 3
1 1(12)16
_______________|
| |
2 2(13)5 6(18)15
| ^
3 3(14)4 7(19)10 11(21)14
| |
4 8(20)9 12(22)13
To report bugs, use the issue tracker.
We welcome any contribution: suggestions, ideas, commits with new futures, bug fixes, refactoring, docs, tests, translations, etc...
If you have question, contact me sacrud@uralbash.ru or #sacrud IRC
channel 
The project is licensed under the MIT license.