Back Office Low Code (backo)

release

pylint test

Jump to Quickstart for a basic setup.

What is backo

It aims at providing a simple and efficient way to create a backend application that exposes a set of REST API routes.

Installation

pip install backo

Quickstart

Here is a sample with a DB (storage full in yaml file) with users to adresses reference

Imagine this Entity Relationship (users ar living in exactly one address, but zero onr more user can live at the same address)

        erDiagram
    direction LR
    classDef className fill:#f9f,stroke:#333,stroke-width:4px
    Users |o--o{ Addresses : live
    Users {
        String name
        String surname
        Bool male
    }
    Addresses {
        String name
        String address
    }

You only will add Ref and Refs to exprime the relationship.

        erDiagram
    direction LR
    classDef className fill:#f9f,stroke:#333,stroke-width:4px
    Users |o--o{ Addresses : live
    Users {
        String name
        String surname
        Bool male
        Ref addr "link one-to-many to Addresses"
    }
    Addresses {
        String name
        String address
        Refs users "link many-to-one to Usres"
    }

It translates into Python code using Backo like following:

from flask import Flask
from backo import Item, DBYmlConnector, Backoffice
from backo import Ref, RefsList, DeleteStrategy

# --- Storage for user
yml_users = DBYmlConnector(path="/tmp")
# --- Storage for addresses
yml_addr = DBYmlConnector(path="/tmp")

# -- Description of the backoffice
my_backoffice = Backoffice("myApp")

# -- Add the collection "users" into this backoffice (with a reference to the futur "addrs" collection)
my_backoffice.add_collection(
    "users",
    Item(
        {
            "name": String(),
            "surname": String(),
            "addr": Ref(coll="addrs", field="$.users", required=True),
            "male": Bool(default=True),
        },
        yml_users,
    ),
)
# -- Add the collection "addrs" into this backoffice (with reference to the "usres" collection)
my_backoffice.add_collection(
    "addrs",
    Item(
        {
            "name": String(),
            "address": String(),
            "users": RefsList(
                coll="users", field="$.addr", ods=DeleteStrategy.MUST_BE_EMPTY
            ),
        },
        yml_addr,
    ),
)


# Your flask application
flask = Flask(__name__)

# -- Add CRUD routes for this application
my_backoffice.add_routes(flask)

Syntax

backo use stricto for structured description language.

Item

Item is the central class in Backo.

It represents a database entity and includes all the methods required for CRUD operations: Create, Read, Update, and Delete.

A generic object is a stricto Dict() object.

Item( description object , db connector )

example

# Describe what a 'cat' is
cat = Item(
        {
            "name": String( required=True, default='Felix'),
            "address": String(),
            "age" : Int()
        },
        db_connector_for_cat)

# Add the cat object into the backoffice object
backoffice.add_collection( "cats", cat )

[!IMPORTANT] Up to now no need to care about _id.

Method	Description
`.create( data :dict )`	Create a new `Item` in the database using the provided `data` dictionary.
`.save()`	saves the current `Item` to the database.
`.load( _id :str )`	loads an `Item` from the database by its `_id`.
`.reload()`	reloads the current `Item` from the database.
`.delete()`	deletes the current `Item` from the database.
`.new()`	creates a new empty `Item` (must be populated with `.set()` and then saved).
`.select()`	retrieves a selection of `Item` from the database based on the selection criteria.

For each function above, an error is triggered in case of something went wrong.

Cardinalities

Relations cardinalities are expressed by the mean of Ref() and RefsList():

Ref(): for 0 or 1 or exactly 1 relations.
RefsList(): for 0 or more or 1 or more relations.

Options

Option for Ref	Default	Description
`coll=`	None	the collection to make the ref
`table=`	None	similar to `coll`
`field=`	None	The reverse field in the targeted collection (use selector to target it)
`rev=`	None	similar to `field`
`ods=`	None	On Delete Strategy see ods

And all options availables in stricto String() fields.

Deletion strategies (`ods`)

ods define the behaviour of the database when a delete occure and the object contain some RefList. For each RefList, you can define the strategy :

DeleteStrategy.MUST_BE_EMPTY (by default) Requires the RefList to be empty before allowing the object to be deleted. If the RefList contains items, the deletion will be blocked and an error will be raised.
DeleteStrategy.DELETE_REFERENCED_ITEMS When deleting the parent object, this strategy also deletes all objects referenced in the RefList. [!Warning] Use with caution, as this causes cascading deletes and may remove many related objects unintentionally.
DeleteStrategy.UNLINK_REFERENCED_ITEMS Instead of deleting the referenced objects, this strategy removes the reference to the deleted object from each referenced item. This is commonly used for many-to-many relationships where you want to delete the parent object but keep the referenced objects intact, but simply cleaning up their links.

Relationship example: Books and Authors

An author can write 0 or many books.

A book can be written only by 1 author.

# Authors write books
author = Item({
    'name' : String(),
    # An author may have written 0 or many books
    'books' : RefsList( coll='book', field="$.autor" )
}, db_connector)

# A book is written by on author
book = Item({
    ... # Some attibutes
    # A book may have 1 or more authors
    authors = RefsList( coll='author', field="$.books", required=True )
}, db_connector )

current_user

current_useris a object containing information of the authenticated user currently connected.

usage

# anywhere in your code
from backo import current_user

print(current_user._id) # The id of the current connected user
print(current_user.login) # A login name or whatever you store as "login"

# check if the user has the given role
if current_user.has_role('teamManager'):
  return True

How to set values to the current_user ?

backo doesnt manage authentication, because there is so much way to authenticate a user (or an app). So you have to do the auth by yourself.

However, using jwt is a goot solution. See Authentication for that.

current_user api

current_user is a very simple Stricto Dict (but can be extended). It contains :

key	type	usage
_id	Stricto String()	the _id of the user.
login	Stricto String()	the login or whatever you store .
roles	Stricto List( String() )	the list of roles for this users. A role is a kid of group the user belongs to
has_role()	function	return True or false to the role givent in param
reset()	function	change the current_user object type. See extend current_user for that

extend current_user

You can extend current_user, adding stuff in its schema, functions… etc.

from backo import current_user, CurrentUser, CurrentUserWrapper

class MyCurrentUser(CurrentUser):


      def __init__(self, obj: CurrentUser):

        CurrentUser.__init__(self, obj)
        self.add_to_model( 'email' , String() )


    """
    a new class child of CuurrentUser
    """
    def my_function(self):
        """
        a Dummy function
        """
        return(f"user {self.login} ({self._id})")

current_user.reset(MyCurrentUser())

# Later in the code
current_user.email = "toto@titi.com"
current_user.my_function() # return the string "user ..."

Authentication

This is an short and uncompleted example to authenticate and fill current_user.

first, the login part. a /login route in flas to make the login, and return a jwt

app = Flask(__name__)
app.secret_key = "super secret key"
# Set the login route
@app.route("/login", methods=["POST"])
def login():
    """
    login load the user from the DB, verify the password and if
    Ok generate a JWT an return it to the client.
    At this point, current_user is not used.
    """
    d = request.json
    login = d["login"]
    password = d["password"]
    # find the user by your way
    user = load_from_db_by_login( login )
    # Do the check of the password
    if not user.check_password( password ):
      return jsonify({"message": "Invalid email or password"}), 401

    token = jwt.encode(
        {
            "exp": datetime.now(timezone.utc) + timedelta(hours=1),
            "user_id": user._id ,
        },
        "myappsecretkey",
        algorithm="HS256",
    )
    response = make_response(json.dumps({"login": "ok"}))
    response.set_cookie("jwt_token", token)
    return response

Second par : The decorator for authenticate the route and fill current_user

def token_required(f):
    @wraps(f)
    def decorated(*args, **kwargs):
        token = request.cookies.get("jwt_token")
        if not token:
            return jsonify({"message": "Token is missing!"}), 401
        try:
            data = jwt.decode(token, "myappsecretkey", algorithms=["HS256"])
        except:  # pylint: disable=bare-except
            return jsonify({"message": "Token is invalid!"}), 401

        # Load the user from the DB and fill current_user
        # we supose roles are store in your user_db
        user = load_from_db_by_id( data["user_id"] )
        current_user.set( { "_id" : user._id, "login" : user.login, "roles" : user.roles })

        return f(*args, **kwargs)
    return decorated

Routes

Automatic routes creation provide the following resources

GET <my-app-name>/coll/<collection name>/<_id> ?_view=<view name>

_view are defined in stricto views

Return the object of this collection by _id.

curl -X GET 'http://localhost/myApp/coll/users/123'

# Equivalent (by default _view=client)
curl -X GET 'http://localhost/myApp/coll/users/123?_view=client'

# Another view
curl -X GET 'http://localhost/myApp/coll/users/123?_view=otherviewname'

Answers can be :

code	data	Description
200	JSON object data	the requested item
401	None	you are not authorized to view this item
404	None	item not found
500	None	server-side error

GET <my-app-name>/coll/<collection name>?<query_string>

Get a list of objects matching the query string. The query string can be with this format

key	value	description
<field>	<value>	matches items where `<field>` equals `<value>`. Example: `surname=donald` finds all items where surname equals to “donald”.
<field>.<operator>	<value>	matches items where `<field>` satisfies `<operator>` with `<value>`. Example: `age.$lt=12` finds items where age is less than 12.
<field>.<subfield>	<value>	Matches items where `<field>` is a nested dictionary containing `<subfield>` equal to `<value>`. Example: `address.number=1` matches items where address.number equals to 1.

list of available operators

key	value	default	description
_view	string	“client”	selects the view (stricto views)
_page	int	-	sets the desired number of items per page in paginated data presentation
_skip	int	-	skips the n-first items of the result list in paginated data presentation.

The request returns a HTTP status 200 with that JSON object:

{
    "result": # list of dict containing objects matched
    "total": # (int) total number of object matched
    "_view": # the _view given in the request
    "_skip": # the _skip given in the request
    "_page": # the _page given in the request
}

Example

Select all users whose name includes ‘do’ and present the result list with 10 items per page.

curl -X GET 'http://localhost/myApp/coll/users/?name.$re=do&_page=10'

POST <my-app-name>/coll/<collection name>

Create a new item for the collection collection name.

Example

curl -X POST 'http://localhost/myApp/coll/users/' -d '{"name":"John","surname":"Rambo"}'

It returns the created user JSON object with a generated unique identifier _id and some _metadatas or an error otherwise.

PUT /<my-app-name>/coll/<collection name>/<_id>

Modify an existing object whose id is _id.

Example

curl -X PUT 'http://localhost/myApp/coll/users/1234' -d '{"name":"Johnny"}'

Modify the users with _id 1234 and return the modified object.

DELETE /<my-app-name>/coll/<collection name>/<_id>

Delete an existing object whose id is _id.

Example

curl -X DELETE 'http://localhost/myApp/coll/users/1234'

Delete the user that has _id = 1234.

PATCH /<my-app-name>/coll/<collection name>/<_id>

Partial change of an existing object whose id is _id. Please refer to the Stricto patch method.

Example

curl -X PATCH  'http://localhost/myApp/coll/users/1234' -d '{"op": "replace", "path" : "$.name", "value": "Gilda"}'

Partial modification of the user with _id 1234 with the patch.

Patch content can be a list of patch operations.

POST /<my-app-name>/coll/<collection name>/_check

Check the validity a field of the item

Please refer to stricto selectors for more details on selectors.

get must provide a json structure in the body :

field	type	descrimtion
item	dict	the data to check. It can be partial, see examples belowv
path	string	the field to check in the item. This is a selector. Please refer to stricto selectors for more details

The answer is a status 200 message with a json structure :

field	type	descrimtion
error	string or null	if null ther is no error, otherwise the error message

Examples :

curl -X POST 'http://localhost/myApp/coll/users/_check' -d '{ "item" : { "name" : "John", "surname" : 32 }, "path" : "$.surname" }'
# will check surname an return a response.data like
{
    'error' : "Must be a string"
}

The response is a status 200 even if the check return an error. The request is correct.

curl -X POST 'http://localhost/myApp/coll/users/_check' -d '{ "item" : { "surname" : "Johnny" }, "path" : "$.surname" }'
# will check surname an return a response.data like
{
    'error' : null
}


curl -X GET 'http://localhost/myApp/coll/users/_check' -d '{ "item" : { "name" : 23, "surname" : "Johnny" }, "path" : "$.surname" }'
# (only the surname is tested. don't car if name is correct or not)
{
    'error' : null
}

Actions routes

Each collection has routes for its actions.

POST /<my-app-name>/coll/<collection name>/_actions/<action_name>/<_id>

is used to call an action.

Meta routes

there is some route availables to get informations on the applications (its structure, rights, etc)

GET /<my-app-name>/_meta

Return the structure of the application as a json with thoses keys :

key	type	description
name	string	The name of the application
collections	array of collection description	list of all collections description

collection description

Describe a collection

key	type	description
name	string	The name ov the collection
item	meta element description	description of an item

meta element description

Describe an element (an item, a key in an item)

key	type	description
type	string	the type of this element. For example “<class ‘backo.item.Item’>” or “<class ‘stricto.string.String’>”
type_short	string	the type of this element, but a short version like “Item” or “String”
description	string	a sort of comment. (optional) or null
require	boolean	mean this element is required or not
in	array of values	if the element must be in a list of value, or null if not.
constraints	boolean	means if there is one or more constraints on this value
default	–	the default value for this field (= null if no default value)
transform	boolean	say there is a transformation function
exists	boolean	false mean this field does not exist and must not be displayed
rights	meta rights description	the description of rights
sub_scheme	meta element description	reccusive description for childs if this object is a Dict or an Item
sub_type	meta element description	description of the content if this object is a List
sub_types	array of meta element description	description of the tuple content if this object is a Tuple

meta rights description

Example

curl -X GET  'http://localhost/myApp/_meta'
# Will return for example

{
  "name": "myApp",
  "collections": [
    {
      "name": "users",
      "item": {
        "type": "<class 'backo.item.Item'>",
        "type_short": "Item",
        "description": null,
        "required": false,
        "in": null,
        "constraints": [],
        "default": null,
        "transform": null,
        "exists": true,
        "rights": {
          "read": null,
          "modify": null
        },
        "sub_scheme": {
          "name": {
            "type": "<class 'stricto.string.String'>",
            "type_short": "String",
            "description": null,
            "required": false,
            "in": null,
            "constraints": [],
            "default": null,
            "transform": null,
            "exists": true,
            "rights": {
              "read": null,
              "modify": null
            },
            "regexp": []
          },
          "surname": {
            "type": "<class 'stricto.string.String'>",
            "type_short": "String",
            "description": null,
            "required": false,
            "in": null,
            "constraints": [],
            "default": null,
            "transform": null,
            "exists": true,
            "rights": {
              "read": null,
              "modify": null
            },
            "regexp": []
          },
          "age": {
            "type": "<class 'stricto.int.Int'>",
            "type_short": "Int",
            "description": null,
            "required": false,
            "in": null,
            "constraints": [
              "func"
            ],
            "default": null,
            "transform": null,
            "exists": true,
            "rights": {
              "read": null,
              "modify": null
            },
            "min": null,
            "max": null
          },
          "site": {
            "type": "<class 'backo.reference.Ref'>",
            "type_short": "Ref",
            "description": null,
            "required": false,
            "in": null,
            "constraints": [],
            "default": null,
            "transform": null,
            "exists": true,
            "rights": {
              "read": null,
              "modify": null
            },
            "regexp": []
          },
          "_id": {
            "type": "<class 'stricto.string.String'>",
            "type_short": "String",
            "description": null,
            "required": false,
            "in": null,
            "constraints": [],
            "default": null,
            "transform": null,
            "exists": true,
            "rights": {
              "read": null,
              "modify": null
            },
            "regexp": []
          }
        }
      }
    }
  ]
}

POST /<my-app-name>/coll/<collection name>/_meta

Ask the backoffice the currents meta information for this collection object.

        "type": ty,
        "type_short" : re.sub(".*\.|\'>", '', ty),
        "description": self.get_as_string(self._description),
        "required": self.get_as_string(self._not_none),
        "in": self.get_as_string(self._union),
        "constraints": self.get_as_string(self._constraints),
        "default": self.get_as_string(self._default),
        "exists": self.exists( self.get_value() ),
        "rights": rights,

Example

For this structure :

def can_see_and_modify_salary(right_name, o, other):

    """
    return true if can read the salary
    """
    global current_user_name
    if current_user_name == o.name:
        return True
    return False

my_backoffice.add_collection(
    "users",
    Item(
        {
            "name" : String(),
            "salary" : Int( default=0, can_read=can_see_and_modify_salary, can_modify=can_see_and_modify_salary ),
        },
        yml_users,
    ),
)

# Logged as "Hector"
curl -X POST 'http://localhost/myApp/coll/users/_meta' -d { 'name' : "John" }
# Will return this structure.
# rights "read" and "modify" are set to false for the salary
{
      "name": "users",
      "item": {
        "type": "<class 'backo.item.Item'>",
        "type_short": "Item",
        "description": null,
        "required": false,
        "in": null,
        "constraints": [],
        "default": null,
        "transform": null,
        "exists": true,
        "rights": {
          "read": null,
          "modify": null
        },
        "sub_scheme": {
          "name": {
            "type": "<class 'stricto.string.String'>",
            "type_short": "String",
            "description": null,
            "required": false,
            "in": null,
            "constraints": [],
            "default": null,
            "transform": null,
            "exists": true,
            "rights": {
              "read": true,
              "modify": true
            },
            "regexp": []
          },
          "salary": {
            "type": "<class 'stricto.string.Int'>",
            "type_short": "Int",
            "description": null,
            "required": false,
            "in": null,
            "constraints": [],
            "default": 0,
            "transform": null,
            "exists": true,
            "rights": {
              "read": false,
              "modify": false
            },
            "regexp": []
          }
        }
    }
}

Internal usage

Typical use case for users and theirs addresses.

# Create an adress, save it in the DB and provide the object with a unique id.
moon_address = backoffice.addrs.create({"name": "moon", "address": "far"})

# Create a user with this address
astro = backoffice.users.create({"name": "neil", "surname": "amstrong", "addr": moon_address._id})

moon_address.users # -> return []
moon_address.reload() # reload data from the DB so that crossed references are updated
moon_address.users # -> return [ astro._id ]

_id

You dont’t have to care about _ids in your item description. Backo will alter schema to add _id for each Item (see stricto schemas for details).

_meta

the db_connector adds meta data to each item by altering its schema.

The provided meta_data_handler give this Dict() :

Dict(
    {
        "ctime": Datetime(),
        "mtime": Datetime(),
        "created_by": Dict(
            {"_id": String(), "login": String()}
        ),
        "modified_by": Dict(
            {"_id": String(), "login": String()}
        ),
    },
),

Workflow and events

Each Item has a specific workflow and triggers specific events.

workflow

The defined states for each item are following:

State	descripion
UNSET	The Item result of a `.new()` function. It can’t be saved in this state
UNSAVED	The Item has been modified and must be saved
SAVED	The Item is saved in the DB and has not been changed since last save

        stateDiagram
    [*] --> UNSET : .new()

    UNSET --> SAVED : .load()
    UNSET --> UNSAVED : .set()
    UNSAVED --> SAVED : .save()
    SAVED --> UNSAVED : .set()
    SAVED --> UNSET : .delete()
    UNSAVED --> UNSET : .delete()

Events

The following events are triggered when the functions above are called:

function	event before	event after
.load()		“loaded”
.save()	“before_save”	“saved”
.delete()	“before_delete”
.create()	None	“created”

Example

Below is a simple use case on how to use these events:

        def rip( event_name, root, me, **kwargs ):
            """
            event_name = "before_delete"
            root = cat Item
            me = cat Item too
            """
            # Do what you want

        cat = Item( {
                'name' : String()
                'birth' : Datetime()
            }
            on=[ ( "before_delete", rip ) ]
        )

Transactions

Soon

CurrentUser

Soon

Logs

The log system is based on logging Python module

You must first design your logging system with handlers. Then you can write the logs outputs.

Example

import logging
from backo import log_system

# To write all file to stderr
log_system.add_handler( log_system.set_streamhandler() )

# To write in a file
log_system.add_handler( log_system.set_filehandler("/var/log/mylog.log") )

# Set the level
log_system.setLevel( logging.INFO )

# create your own sub logger with its specific logging level
log = log_system.get_or_create_logger("custom")
log.setLevel(loggind.DEBUG)

log.debug("hey this is my first debug message")

Advanced use

You can select a specific logger and modify it by adding/removing handlers and changing its level.

log = log_system.get_or_create_logger("custom")
log.setLevel(loggind.DEBUG)
log.addHandler ( my_own_handler )
# ...

current loggers

Currently available loggers are :

logger	description
backoffice	The main Backoffice system
Item	The database itself (CRUD operations )
ref	Ref and RefsList objects
transaction	transactions and roolback
yml	yaml database connector

Tests & co

For personal use only.

# all tests
python -m unittest tests
# or for a specific test
python -m unittest tests.TestDict.test_simple_type

# reformat
python -m black .

# pylint
pylint $(git ls-files '*.py')

# coverage
coverage run -m unittest tests
coverage html # report under htmlcov/index.html
firefox htmlcov/index.html

Building a new release

For personal use only.

# Modify changelog
# modify pyproject.toml
git add -u
git commit -am 'preparing 0.0.x'
git push
git tag -a 0.0.x -m '0.0.x'
git push origin tag 0.0.x

# publish a new relase in github interface, based on tag

Back Office Low Code (backo)

What is backo

Installation

Quickstart

Syntax

Item

example

Cardinalities

Options

Deletion strategies (ods)

Relationship example: Books and Authors

current_user

usage

How to set values to the current_user ?

current_user api

extend current_user

Authentication

Routes

GET <my-app-name>/coll/<collection name>/<_id> ?_view=<view name>

GET <my-app-name>/coll/<collection name>?<query_string>

Example

POST <my-app-name>/coll/<collection name>

Example

PUT /<my-app-name>/coll/<collection name>/<_id>

Example

DELETE /<my-app-name>/coll/<collection name>/<_id>

Example

PATCH /<my-app-name>/coll/<collection name>/<_id>

Example

POST /<my-app-name>/coll/<collection name>/_check

Actions routes

POST /<my-app-name>/coll/<collection name>/_actions/<action_name>/<_id>

Meta routes

GET /<my-app-name>/_meta

collection description

meta element description

meta rights description

Example

POST /<my-app-name>/coll/<collection name>/_meta

Example

Internal usage

_id

_meta

Workflow and events

workflow

Events

Example

Transactions

CurrentUser

Logs

Example

Advanced use

current loggers

Tests & co

Building a new release

Deletion strategies (`ods`)