mongoengine-goodjson 0.9.3

More human readable JSON serializer/de-serializer for MongoEngine

What This?

This script has MongoEngine Document json serialization more-natural.

Why this invented?

Using MongoEngine to create something (e.g. RESTful API), sometimes you might want to serialize the data from the db into JSON, but some fields are weird and not suitable for frontend/api:

{
  "_id": {
    "$oid": "5700c32a1cbd5856815051ce"
  },
  "name": "Hiroaki Yamamoto",
  "registered_date": {
      "$date": 1459667811724
  }
}

The points are 2 points:

• _id might not be wanted because jslint disagrees _ character unless declaring jslint nomen:true

• There are sub-fields such $oid and $date. These fields are known as MongoDB Extended JSON. However, considering MongoEngine is ODM and therefore it has schema-definition methods, the fields shouldn’t have the special fields. In particular problems, you might get No such property $oid on undefined error when you handle above generated data on frontend.

To solve the problems, the generated data should be like this:

{
  "id": "5700c32a1cbd5856815051ce",
  "name": "Hiroaki Yamamoto",
  "registered_date": 1459667811724
}

Making above structure can be possible by doing re-mapping, but if we do it on API’s controller object, the code might get super-dirty:

"""Dirty code."""
import mongoengine as db


class User(db.Document):
  """User class."""
  name = db.StringField(required=True, unique=True)
  registered_date = db.DateTimeField()


def get_user(self):
  """Get user."""
  models = [
    {
      ("id" if key == "_id" else key): (
        value.pop("$oid") if "$oid" in value and isinstance(value, dict)
        else value.pop("$date") if "$date" in value and isinstance(value, dict)
        else value  #What if there are the special fields in child dict?
      )
      for (key, value) in doc.items()
    } for doc in User.objects(pk=ObjectId("5700c32a1cbd5856815051ce"))
  ]
  return json.dumps(models, indent=2)

To give the solution of this problem, I developed this scirpt. By using this script, you will not need to make the transform like above. i.e.

"""A little-bit clean code."""

import mongoengine as db
import mongoengine_goodjson as gj


class User(gj.Document):
  """User class."""
  name = db.StringField(required=True, unique=True)
  registered_date = db.DateTimeField()


def get_user(self):
  """Get user."""
  return model_cls.objects(
    pk=ObjectId("5700c32a1cbd5856815051ce")
  ).to_json(indent=2)

How to use it

Generally you can define the document as usual, but you might want to inherits mongoengnie_goodjson.Document or mongoengnie_goodjson.EmbeddedDocument.

Here is the example:

"""Example schema."""

import mongoengine_goodjson as gj
import mongoengine as db


class Address(gj.EmbeddedDocument):
    """Address schema."""

    street = db.StringField()
    city = db.StringField()
    state = db.StringField()


class User(gj.Document):
    """User data schema."""

    name = db.StringField()
    email = db.EmailField()
    address = db.EmbeddedDocumentListField(Address)

Feature: Follow Reference

Adding documents with ReferenceField, the fields are serialized as ObjectId by default:

model.py

import mongoengine as db
import mongoengine_goodjson as gj


class Book(gj.Document):
  """Book information model."""

  name = db.StringField(required=True)
  isbn = db.StringField(required=True)
  author = db.StringField(required=True)
  publisher = db.StringField(required=True)
  publish_date = db.DateTimeField(required=True)


class User(gj.Document):
  firstname = db.StringField(required=True)
  lastname = db.StringField(required=True)
  books_bought = db.ListField(db.ReferenceField(Book))
  favorite_one = db.ReferenceField(Book)

The example of generated output

{
  "id": "570ee9d1fec55e755db82129",
  "firstname": "James",
  "lastname": "Smith",
  "books_bought": [
    "570eea0afec55e755db8212a",
    "570eea0bfec55e755db8212b",
    "570eea0bfec55e755db8212c"
  ],
  "favorite_one": "570eea0bfec55e755db8212b"
}

This seems to be good deal for Reference Field, but sometimes you might want to generate the Document with Referenced Document like Embedded Document:

{
  "id": "570ee9d1fec55e755db82129",
  "firstname": "James",
  "lastname": "Smith",
  "books_bought": [
    {
      "id": "570eea0afec55e755db8212a",
      "name": "ドグラ・マグラ (上)",
      "author": "夢野 久作",
      "publisher": "角川文庫",
      "publish_date": "1976-10-01",
      "isbn": "978-4041366035"
    },
    {
      "id": "570eea0bfec55e755db8212b",
      "name": "ドグラ・マグラ (下)",
      "author": "夢野 久作",
      "publisher": "角川文庫",
      "publish_date": "1976-10-01",
      "isbn": "978-4041366042"
    },
    {
      "id": "570eea0bfec55e755db8212c",
      "name": "The Voynich Manuscript: Full Color Photographic Edition",
      "author": "Unknown",
      "publisher": "FQ Publishing",
      "publish_date": "2015-01-17",
      "isbn": "978-1599865553"
    }
  ],
  "favorite_one": {
    "id": "570eea0bfec55e755db8212b",
    "name": "ドグラ・マグラ (下)",
    "author": "夢野 久作",
    "publisher": "角川文庫",
    "publish_date": "1976-10-01",
    "isbn": "978-4041366042"
  }
}

Making this format can be done by making Document.objects query for each reference. However, doing it, the code would be also dirty:

def output_references():
  user = User.objects(pk=ObjectId("570ee9d1fec55e755db82129")).get()
  user_dct = json.loads(user.to_json())
  user_dct["books"] = [
    json.loads(book.to_json()) for book in user.books_bought
  ]
  user_dct["favorite_one"] = json.loads(user.favorite_one.to_json())
  return jsonify(user_dct)
  # ...And what if there are references in the referenced document??

To avoid this annoying problem, this script has new function called Follow Reference since 0.9. To use it, you can just set follow_reference=True on serialization:

def output_references():
  user = User.objects(pk=ObjectId("570ee9d1fec55e755db82129")).get()
  return jsonify(json.loads(user.to_json(follow_reference=True)))

Note that setting follow_reference=True, Document.to_json checks the reference recursively until the depth is reached 3rd depth. To change the maximum recursion depth, you can set the value you want to max_depth:

def output_references():
  user = User.objects(pk=ObjectId("570ee9d1fec55e755db82129")).get()
  return jsonify(json.loads(user.to_json(follow_reference=True, max_depth=5)))

Not implemented list

The following types are partially implemented because there aren’t any corresponding fields on MongoEngine:

Type	Encoder	Decoder
Regex	white_check_mark:	x:
MinKey	white_check_mark:	x:
MaxKey	white_check_mark:	x:
TimeStamp	white_check_mark:	x:
Code	white_check_mark:	x:

The following document types are not implemented yet:

• DynamicDocument

• DynamicEmbeddedDocument

• MapReduceDocument

Btw I don’t think above documents implementations are needed because they can be handled by using multiple-inheritance. If you couldn’t do it, post issue or PR.

FollowReference Decoder

Since 0.9, this script supports Follow Reference, but it doesn’t support decoder. Passing “followed reference” dict to ReferenceField, it recognized id field only. This behavior will be fixed at 0.10.

Contribute

This scirpt is coded on TDD. i.e. Writing a test that fails, and then write the actual code to pass the test. Therefore, virtualenv, nose and tox will be needed to code this script. In addtion, you will need to have MongoDB installed and it must be running on the computer to run the tests.

In addition, you can use gulp to watch the file changes.

License (MIT License)

Copyright (c) 2016 Hiroaki Yamamoto

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.