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A pure Python document and graph database engine

Project description

DocNetDB

A pure Python document and graph database engine

Breaking changes are to expect during beta.

Summary

Features

  • Create vertices
  • Add elements in them (with a dict-like style)
  • Link them with edges (as an oriented graph or not)
  • Save the database as JSON

Strengths :

  • Simple use
  • Storage in one readable and editable file (JSON format)
  • Subclassable vertices and edges for complex uses
  • Directed and non-directed edges can cohabit in the same graph

Weaknesses :

  • Not designed to be fast
  • Data is entirely loaded in memory
  • Elements must be JSON-serializable

Installation

Just run :

python3 -m pip --user install docnetdb

Or if you use a virtual environment, which is way better :

pip install docnetdb

Usage

Create the DocNetDB object

It's the database object. Give it the path to the file which will be read (if existing) of created (if not).

from docnetdb import DocNetDB
import pathlib

# You can use a string...
database = DocNetDB("subfolder/file.ext")

# ...or a Path.
database = DocNetDB(pathlib.Path(".") / "subfolder" / "file.ext")

Create and insert vertices

A Vertex is a dict-like object that contains elements. These should be JSON-serializable as the DocNetDB is written in the JSON format.

from docnetdb import Vertex

# You can create an empty Vertex...
rush_hour = Vertex()
# ...and assign elements to it like items in a dict.
rush_hour["name"] = "Rush Hour"
rush_hour["length"] = 5.25
rush_hour["url"] = "https://www.youtube.com/watch?v=OXBcBugpHZg"

# Or you can provide directly a dict with initial data.
initial_data = dict(
    name="Nyakuza Manholes",
    length=6.62,
    url="https://www.youtube.com/watch?v=GDxS8oK6hCc"
)
manholes = Vertex(initial_data)

Vertices are not inserted in the database by default.

# You can easily check if the Vertex is inserted in a database.
rush_hour.is_inserted # Returns False

# And also check if a DocNetDB object contains a Vertex.
rush_hour in database # Returns False

Every Vertex in a database has a place (equivalent to an ID), that starts at 1. A Vertex that is not inserted have a place equal to 0.

# To insert a Vertex, just run :
database.insert(rush_hour) # Returns the place (1 in this case)

# You can verify it with :
rush_hour.is_inserted # Returns True
rush_hour.place # Returns 1
rush_hour in database # Returns True

# Let's add our second Vertex.
database.insert(manholes) # Returns the place (2 in this case)

# You can access a Vertex from its place in the DocNetDB with item style.
database[1] is rush_hour # Returns True
database[2] is manholes # Returns True

The object is the same, so its possible to work directly with the named variables, and modify the content of the DocNetDB as well.

Search and remove vertices

You can search for vertices in a DocNetDB.

# Get the vertices that have a length superior to 6 minutes
def custom_gate(vertex):
    return vertex["length"] > 6

found = database.search(custom_gate) # Returns a generator

It doesn't matter if a vertex doesn't have a "length" element, as the KeyError is automatically captured.

You can remove vertices from the DocNetDB.

# Delete the filtered vertices (just "manholes" in this case)
for vertex in list(found):
    database.remove(vertex)

# "manholes" still exists, it was just detached from the database.
manholes["name"] # Returns "Nyakuza Manholes"
manholes.is_inserted # Returns False

Save the database

If the file didn't exist, this command creates it.

database.save()

Add edges between the vertices

# Let's create a Vertex for the demo
hat = Vertex({"game":"A Hat In Time"})
database.insert(hat)

from docnetdb import Edge
edge = Edge(start=hat, end=rush_hour, label="ost", has_direction=True)

The parameters of the Edge init are the following :

  • start : the first Vertex of the edge
  • end : the last vertex of the edge
  • label : a label for the edge ("" by default)
  • has_direction : whether the edge has a direction between the vertices or not (True by default)
# Let's insert this edge in the database
database.insert_edge(edge)

Understand anchors in an edge

This specificity of DocNetDB to have both directed and non-directed edges has led me to implement a feature, that I called the edges anchors. This is just a way to see the edge from a different point of view. Let's see the example of our "OST" edge from the "A Hat In Time" game vertex to the "Rush Hour" music vertex.

edge.start # Returns the 'hat' vertex
edge.end # Returns the 'rush_hour' vertex

# Then, let's anchor the 'hat' vertex in our edge
edge.change_anchor(hat)
edge.anchor # Returns the 'hat' vertex
edge.other # Returns the 'rush_hour' vertex
edge.direction # Returns 'out'

# Let's specify another anchor
edge.change_anchor(rush_hour)
edge.anchor # Returns the 'rush_hour' vertex
edge.other # Returns the 'hat' vertex
edge.direction # Returns 'in'

This is very handy, especially when searching for edges, as we'll see in the next part.

Search and remove edges

The search_edge method of a DocNetDB class is very handy. It can search for edges connected to a vertex, and filter it by the other end of the edge, its label and/or its direction. You should see its documentation for more information.

Here, we'll search for all the vertices connected to our 'Rush Hour' vertex.

found = database.search_edge(rush_hour)

# This is the equivalent of this line
found = database.search_edge(rush_hour, v2=None, label=None, direction="all")

# Like all the search functions, the returned object is a generator.
edges = list(found)

# The returned edges have an anchor, which is the first vertex of the search.
edges[0].anchor # Returns the "rush_hour" vertex
edges[0].other # Returns the "hat" vertex
edges[0].direction # Returns "in"

# Let's delete the first edge (and the only in this case)
database.remove_edge(edges[0])

Other uses of the DocNetDB

# Iterate over all the vertices
for vertex in database.vertices():
	pass

# Or just
for vertex in database:
	pass

# Get the number of inserted vertices
len(database)

# Iterate over all the edges
for edge in database.edges():
	pass

Subclassing the Vertex class

You can subclass it, and that is something I haven't found in other libraries (I guess). Thus you can define new methods, conditions when adding/modifying an element, etc. Some examples are given in the vertex_examples.py file.

Let's make a Vertex that add automatically the datetime of creation, and must have a name to be inserted.

import datetime
from docnetdb import Vertex

class DatedVertex(Vertex):
    """A Vertex that keeps track of the time and has a name."""

    def __init__(self, initial_dict):
        """Override the __init__ method."""

        # Let's create the Vertex first by calling the Vertex __init__.
        super().__init__(initial_dict)

        # Let's then add the creation date.
        # We use the ISO format as the value has to be JSON-serializable.
        # Be careful, the init is also called on database load, thus the condition.
        if "creation_date" not in self:
            self["creation_date"] = datetime.datetime.now().isoformat()

    def is_ready_for_insertion(self)
        """Override the is_ready_for_insertion method."""

        # If this method returns False on insertion, il will be cancelled.
        return "name" in self

To pack data in the database file on save, and load correctly, we can override the from_pack and pack methods. Some examples are given in the docnetdb/examples/vertices.py file.

Subclassing the Edge class

It's quite the same. Some examples are given in the docnetdb/examples/edges.py file.

Documentation

I've not exported it yet, but I try to give proper docstrings to my code, so check them out if you want.

Project details


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