docnetdb 0.3.1

A pure Python document and graph database engine

DocNetDB

A pure Python document and graph database engine

The graph part is coming soon.

Features

Strengths :

• Simple use !
• In one readable and editable file
• The Vertex class is subclassable

Weaknesses :

• Due to its design, not fast as light
• All the data is loaded in memory

Usage

Creating a 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")

Creating 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)

Insert vertices in the database

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.

Save the database to the file

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

database.save()

Use the DocNetDB

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

And others :

len(database) # Return the number of inserted vertices

database.all() # Return a generator of all inserted vertices

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, process on insertion or conditions when adding/modifying an element. Some examples are given in the vertex_examples.py file.

Let's make a Vertex that add automatically the datetime of creation and the datetime of insertion in the DocNetDB.

import datetime
from docnetdb import Vertex

class DatedVertex(Vertex):
    """A Vertex that keeps track of the time."""

    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.
        self["creation_date"] = datetime.datetime.now().isoformat()

    def on_insert(self):
        """Override the on_insert method."""

        self["insertion_date"] = datetime.datetime.now().isoformat()

    @classmethod
    def from_dict(cls, dct):
        """Override the from_dict method."""

        # Here's the thing.
        # If we don't do that, the next time the file will be loaded by a DocNetDB,
        # the data is going to be encapsulated in Vertex objects.
        # So we add this method to indicate to the database how to load th data.

        return DatedVertex(dct)

Here, the from_dict method is not that useful : we could work with Vertex objects as well when loading the file, as the DatedVertex class is only useful before and while inserting vertices in the DocNetDB. But if we want to add custom methods, like one which could calculate the time between the creation and the insertion of the DatedVertex, then we would want the database to load the data in this specific class.

We can provide the function like this.

database = DocNetDB("db.db", vertex_creation_callable=DatedVertex.from_dict)