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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/

Nested sets traversal

The nested set model is a particular technique for representing nested sets (also known as trees or hierarchies) in relational databases.

Installing

Install from github:

pip install git+http://github.com/uralbash/sqlalchemy_mptt.git

PyPi:

pip install sqlalchemy_mptt

Source:

pip install -e .

Usage

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.id

Now you can add, move and delete obj!

Insert node

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

Delete node

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

Update node

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

Move node (support multitree)

Nested sets multitree

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

Support and Development

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 IRC Freenode

License

The project is licensed under the MIT license.