dynamof 2.0.2

A small interface for more easily making calls to dynamo using boto.

Dynamof

A small :fire: interface for more easily making calls to dynamo using boto. No bloated ORM - just functions that make creating the complex objects needed to pass to boto3 quick and easy.

Basic Features

• Simplifying boto3 function APIs (see an example)

If you've ever used boto3 directly before you know the pain that can exist trying to write a dynamic KeyCondition or ConditionExpression. dynamof does these things for you.

• Standardizing boto3 error handling (see an example)

If you've ever used boto3 directly you know that handling errors is the absolute worst... how much time I've spent googling how to catch this error or that error.... and they're all different! dynamof wraps the calls to boto3, catches all of its errors in all of their uniquely identifiable ways and exposes a concise error api that works with the standard try ... except.

• Customizable api (see an example)

Because doing it how I do it probably isn't for you.

dynamof wraps the boto3.client('dynamodb') (docs) functions exposing much easier to use api's. It's written in a functional style with the goal to be as useful to anyone in any way as possible. The wrappers around boto3 functions are split into two parts: operations and runners. A runner runs a specific operations. The operation contains all the necessary information for a dynamo action to be ran. This means, you don't have to use dynamof to actually interact with dynamo if you don't want to but you could still use it as a utility to more easily generate the complex objects that are passed to boto3 functions.

Example: Create a table in dynamo

from boto3 import client
from dynamof.executor import execute
from dynamof.operations import create

client = client('dynamodb', endpoint_url='http://localstack:4569')

execute(client, create(table_name='users', hash_key='username'))

First thing to note... execute(client, some_operation(...)) isn't sexy... and as engineers sexy is important. Because dynamof is a simple functional utility library its very easy to bend it into any api you would like.

Example: Customize the way you call dynamof

##
## Keep it functional
##

from functools import partial
from boto3 import client
from dynamof.executor import execute
from dynamof.operations import create

client = client('dynamodb', endpoint_url='http://localstack:4569')
db = partial(execute, client)

# Now calling looks like
db(create(...))
db(find(...))
db(update(...))

##
## Make it a class
##

class DB:
  def __init__(self):
    self.client = client('dynamodb', endpoint_url='http://localstack:4569')
  def find(*args, **kwargs):
    return execute(self.client, find(*args, **kwargs))

db = DB()
db.find(table_name='users', key={ 'id': 21 })

##
## Make it a table specific class
##

class Table:
  def __init__(self, table_name):
    client = client('dynamodb', endpoint_url='http://localstack:4569')
    self.table_name = table_name
    self.db = partial(execute, client)
  def find(*args, **kwargs):
    return self.db(find(self.table_name, *args, **kwargs))
  def update(*args, **kwargs):
    return self.db(update(self.table_name, *args, **kwargs))
  def delete(*args, **kwargs):
    return self.db(delete(self.table_name, *args, **kwargs))


users = Table('users')

users.find(key={ 'id': 21 })
users.update(key={ 'id': 21 }, attributes={ 'username': 'new_username_1993_bro' })
users.delete(key={'id': 21 })

Example: Catch errors from dynamof

from dynamof.exceptions import (
    UnknownDatabaseException,
    ConditionNotMetException,
    BadGatewayException,
    TableDoesNotExistException
)

try:
  db(update(
    table_name='users',
    key={ 'id': 43 },
    attributes={ 'username': 'sunshie' }))
except TableDoesNotExistException:
  # Handle case where table doesn't exist
except ConditionNotMetException:
  # Handle case where the condition wasn't met (the item you tried to update didn't exist)
except BadGatewayException:
  # Handle a network error
except UnknownDatabaseException:
  # Handle an unknown issue

Example: Use dynamof as sugar to call boto3 yourself

from dynamof import operations
from dynamof.conditions import attr


query = operations.query(
  table_name='books',
  conditions=attr('title').equals('The Cost of Discipleship'))

result = client.query(**query.description)

Why Dynamof?

If you're using python and dynamo you have 2 options: an ORM like PynamoDB or Boto3. Kudos to the people who made Pynamo, its great, but it really doesn't scale well. And your stuck with the ORM features even if you don't want them. Interacting with Boto3 directly is a pain. With things like KeyConditions and ConditionExpressions being so difficult to easily grasp you end up duplicating a lot of code in your database/repository/DAL layer. This was my experience. In my early day's I used Pynamo. Once I got tired of trying to bend it to my will at scale I started using Boto3 directly. But... this was still annoying. I wanted a non-opinonated library that could sit on top of Botot3 and do the repetitive, annoying to code work for me. dynamof was born.

API Documentation

dynamof.operations
dynamof.conditions
dynamof.exceptions
dynamof.builder

Operations

See the code
See the test

create(table_name, hash_key, allow_existing=False)

See boto3 docs

Parameter	Required	Data Type	Description	Example
table_name	yes	str	The name to assign the table your creating	'users'
hash_key	yes	str	The hash key (primary key) for your table	'user_id'
allow_existing	no	bool	Creating a table that already exists will throw an error in boto3. Passing True here will ignore that error if its raised and ignore it.	True

:orange_book: Limitations

• Cannot specify range key
• Cannot specify complex hash key (hash key and range key)
• Cannot specify indexes
• Other boto3 parameters not implemented (BillingMode, ProvisionedThroughput, StreamSpecification, SSESpecification, Tags)

find(table_name, key)

See boto3 docs

Parameter	Required	Data Type	Description	Example
table_name	yes	str	The name of the table to find an item in	'users'
key	yes	str|dict	The key (primary key) of the item to find. If a string is passed it is associated with id by default. If an object is passed the first key and value are used to find the item	22 or { 'username': 'sunshie' }

:orange_book: Limitations

• Cannot use projection expressions
• Other boto3 parameters not implemented (ConsistentRead, ReturnConsumedCapacity)

add(table_name, item, auto_inc=False)

See boto3 docs

Parameter	Required	Data Type	Description	Example
table_name	yes	str	The name of the table to add the item to	'users'
item	yes	dict	The item to be added to the table in key value pairs. If auto_inc is not set to true then this dict must include a valid key value pair for the table's hash key	{ 'username': 'sunshie', 'user_status': 'unleashed' }

:orange_book: Limitations

• boto3 parameters not implemented: ReturnItemCollectionMetrics, ReturnConsumedCapacity, ReturnValues

:closed_book: Known Issues

• When the table you're trying to add to does not exist the put_item function in boto3 does not throw the expected ClientError with the table not found code and message. Instead, it throws a bad gateway error. So, when calling add you cannot depend on the TableDoesNotExistException. In a future version you will be able to use an additonal method to check if the table exists if needed.

update(table_name, key, attributes)

See boto3 docs

Parameter	Required	Data Type	Description	Example
table_name	yes	str	The name of the table to update the item on	'users'
key	yes	str|dict	The key (primary key) of the item to find for updating. If a string is passed it is associated with id by default. If an object is passed the first key and value are used to find the item	22 or { 'username': 'sunshie' }
attributes	yes	dict	The key values patch/set on the record	{ 'rank': 23 }

:orange_book: Limitations

• Cannot allow setting parameters for ReturnValues, ReturnConsumedCapacity, ReturnItemCollectionMetrics

delete(table_name, key)

See boto3 docs

Parameter	Required	Data Type	Description	Example
table_name	yes	str	The name of the table to delete the item from	'users'
key	yes	str|dict	The key (primary key) of the item to delete. If a string is passed it is associated with id by default. If an object is passed the first key and value are used to find the item	22 or { 'username': 'sunshie' }

:orange_book: Limitations

• Cannot allow setting parameters for ReturnValues, ReturnConsumedCapacity, ReturnItemCollectionMetrics

query(table_name, conditions)

See boto3 docs

Parameter	Required	Data Type	Description	Example
table_name	yes	str	The name of the table to execute the query on	'users'
conditions	yes	dynamof.conditions.Condition	This value should be built using the dynamof.conditions module. See the docs on that module.	attr('username').equals('sunshie') will build a proper Condition to pass.

:orange_book: Limitations

• Cannot do pagination
• Cannot set limits
• Cannot query indexes
• Cannot allow setting parameters for ReturnValues, ReturnConsumedCapacity, ReturnItemCollectionMetrics

Conditions

The dynamof.conditions module provides utility methods that make it simple to generate the complex data object boto3 needs when specifying conditions for querying, scanning, and other operations. Looking at the docs for the query function you'll see KeyConditionExpression. This is the parameter this module was created to build.

Example

from dynamof.conditions import attr

cond = attr('username').equals('sunshie')

cond.expression
# 'username = :username'

cond.attr_values
# { ":username": { "S": "sunshie" } }

attr(name)

Parameter	Required	Data Type	Description	Example
name	yes	str	The name of the attribute to begin using on a condition. Could be a column you want to match exactly or if its a number type then it could be a column you want to check for > or < on	'username'

The attr function returns a dynamof.conditions.Attribute that contains three methods

• equals(value)
• greater_than(value)
• less_than(value)

Where value is always the value to use in the conditional comparison you build.

cand(*conditions)

Takes any number of condition expressions and combines them using the and rule.

Parameter	Required	Data Type	Description	Example
conditions	yes	*dynamof.conditions.Condition	Takes any number of Condition instances	cand(attr('points').less_than(50)

Roadmap

• :white_check_mark: only use client & kill resource
• :white_check_mark: testing
• :white_check_mark: linter
• :white_check_mark: implement query
• :white_check_mark: implement response object & destructure response Item tree
• :white_check_mark: handle errors
• :white_check_mark: documentation setup travis move builder to core module
• :checkered_flag: version 1.0.0
• implement scan
• query support pagination
• query support indexes
• support projection expressions
• support filter expressions
• :checkered_flag: version 1.2.0
• batch operations
• metadata operations
• update table operation
• ...
• :checkered_flag: version 2.0.0