[PART 5] NuTracker ReactJS app - Add Login & Profile using Router

In the previous part we finished the dashboard read functionality, now we want to add the skeleton for other pages:

- Login
  In this page the user will be able to login to their account and the dashboard won't show unless the user is logged in.

- Profile
In this page the user will be able to update their daily nutrition goals that they can track in the dashboard.

to be able to have multiple 'pages' in react and navigate from one to one, we need something that can switch the rendered content based on what we want, we can do that with if statements in the App components and store some location state, but why invent the wheel.

React Router

every major single page app web framework has the routing concept and functionality to interact with the usual browser urls and switch the content based what user should see.

for example on the profile page I want the url path to be /profile, and for login to be /login and so on.
in more advanced cases you want the users to be able to bookmark a page and be able to get back to that page with state they left it on and that is tricky in single page apps because as in our case we deal with state which doesn't read anything from url and everything is just stored in browser memory.


for this PR I only added the navigation and authentication protection of dashboard & profile using react router, in future we can try to do something like making the date be a url parameter so users can bookmark specific dates in their dashboard.

here is the core lines that hold the routing logic (see routes.js)

everything added to enable router is in this PR, and I commented on the PR changes to explain each change.

Things to note

1- React Router manages its own state, it's not managed by redux

Yes things can get a bit messy because now we have two different sources of state and this means if we want a button to udpate the url and pass filters for examples (like the date navigation) then we need to let our components to read that from router state and not from the redux stored state.

there is a library that synchronizes redux and router called connected-react-router

more about this here:
- https://reacttraining.com/react-router/core/guides/redux-integration
- https://redux.js.org/advanced/usagewithreactrouter


2- we can check authentication and decide to either redirect to login or allow and render the component by adding custom PrivateRoute component (see routes.js), see also how the login page will redirect back to the referrer (the page the user tried to access before they were redirected to login)



how the app looks right now:

the dummy login page:

 

 

our lovely dashboard:

and our dummy profile page:

In the next part I'll be covering PropTypes and how to write unit tests for components then we can add our first form to allow the user to add entries to their day.

[PART 4] NuTracker, ReactJS application - Finish Dashboard Read functionality

In the previous part we added the first call to the async api to do search, now we will build on that to call more apis, and to add more components on the page to finish up the Display flows (i.e. what doesn't require writes / forms) :

• search
• this allows the user to find a specific food and choose to add an entry for it to their day to record that they consumed a specific portion of that food.
• show entries
• This feature is to allow users to see what they recorded as a list of entries, each entry represents a food the user added on a specific date.
• show progress bars
• The user will be able to set goals like how many calories, proteins, fats they want to consume daily and these bars will calculate from the entries they added how close they are to their daily goals
• reload entries & progress metrics when date change 
• This is to provide the ability for the users to go back in history and see their entries.

all this is in general similar to the steps I did before:
- add presentation component
- add add actions (api calls or anything else) & reducers ( store the responses in the state and calculate new state if the date changed for example )
- add container component to pass the props to the presentation


all the code for this day is in this pull request ( so you can check exactly what was added and changed), I have also added comments on some files there to explain a little bit.
It's easier to see and navigate files in the "Files Changed" tab in Github PR page

Things Worth noting

 Components Interaction

Up to this point the dashboard didn't have any interaction across components
but in this PR I added the Date navigator which when a user navigates in one direction should load the Entries they created for that new Date they are on, I addition the progress metrics should update according to the new entries.
the way I did this was :
1- when dashboard first loads it just loads the current day information, so the entries list component will  (in componentDidMount) and fetch today's entries).
2- if the user go back in date navigator that triggers a redux action (PERIOD_CHANGED, see dateNavActions.js)
3- the period reducer will update the state with the new start/end dates
4- Our DayEntries component uses state.period as props, so when the state changed because of the date navigation action above, our component will be rerendered.
5- since this is a rerender and not mounting, we have to use the componentWillReceiveProps life cycle method to trigger a new redux action to fetch the entries for the new date period.

 Introducing RequestBuilder

this class is a helper to be used by the repos to inject headers and parse reposne as json, this saves us from repeating this logic everywhere.

Adding User info to state

Since we now want to show progress bars about user goals, I added an api call through userRepo to get the user profile from backend (see Dashboard component), there was no login needed because I hardcoded the user token in the request builder, this way we have real user information without being blocked on login being ready to do this work but in the same time we deal with real data model of the user.


In the next part I plan to :
1- create a dummy login page
2- use react-router to have multiple pages in our app (login, dashboard, profile) each with it's own url

Using Windows 10 built in bash to ssh to ec2 instance

Using Windows 10 built in bash to ssh to ec2 instance

detailed steps to install bash on windows here: https://www.thewindowsclub.com/run-bash-on-windows-10

Summary:

0- enable windows subsytem for linux
1- open cmd
2- type bash
3- accept and create a unix user account
4- wait to finish
6- you may need to reboot

reopen cmd and type bash, you should see your cmd prompt changed.

5- to ssh to ec2 you need .pem key file that you download when you create the instance
6- copy that file under /home or something else but not under /mnt/* (windows files) because the next step will not work, the file has to be in a linux directory (bash in windows can't change windows files permissions)
7- we have to run this command :
$ chmod 400 pem_file.pem
because otherwise you will get an error that this key permissions are too open (not secure enough).
8- the command is ssh -i "pem_file.pem" ec2-user@123.456.897  (replace the pem file name and ip with your values).

now you can connect from windows terminal without ssh client/PuTTy  and this bash can be used for other bash command and tools like telnet etc.. fun :)

Online IDE stackblitz.com :)

I stumbled upon this neat online IDE, where you can :

- instantly start, share and run code
- use npm dependencies and install what you need quickly
- you can drag drop files from your computer
I'm yet to explore it but seems very promising

it also has a neat feature to embed itself in blogs like this one so that's awesome because now I can show live examples of running code and share them with my readers !

all I had to do is include an iframe with url to my test project on their website

this is an example of a react project   :)




Kudos to the people who create this cool stuff and share with us !

Gensim NLP and TF-IDF document search example

In this blog I'll try to use an NLP (Natural language processing) library to get to:
- know some basic concepts and
- try to search a data set of books metadata (author, title, summary) to respond to user query

Setup
 you need:
- Anaconda (python environment management tool), get it here
Anaconda works by creating an isolated installation of python with the packages needed and it won't affect other environments so you can run different versions of python and other python libraries without conflicts
- code: https://github.com/blabadi/gensim-books

- setup the environment (in shell window or in anaconda prompt) run:
conda create gensim_env python=3.5 gensim nltk jupyter
this will install the packages needed
- navigate to the code directory, run:
jupyter notebook

this will open the server web page and you can select the notebook that we need now : gensimWord2Vec

Code
https://github.com/blabadi/gensim-books/blob/master/gensimTFIDF.ipynb

[ Part 3 ] First Async call, redux-thunk

Previous Part (adding redux): http://dev.basharallabadi.com/2018/09/part-2-nutracker-reactjs-application.html

By default the store only understands object dispatched actions, i.e. it won't support async calls out of the box neither functions, which conflicts with our need to call an api asynchronously and get the results and returns those results to our reducers to update the state.

Redux Thunk

The simplest approach to achieve what we need is to use something called middleware in redux that can pre process our actions and then proceed to the store when it's done.
Redux thunk is a middleware library that knows how to handle a function received as a dispatched action from a component then based on the result it can dispatch more actions to the store to notify our reducers with the results.
mainly we use it to process async calls and based on the result (success/fail) we ask it to dispatch the proper actions when.

First lets update our foodRepo to actually call an api:
- install corss-fetch npm install --save cross-fetch to use the fetch API and get promises for our async calls.
- renamed the mock method in foodRepo to findFoodMock(), and created new one for the real call which does a fetch call to our api and parse the json body.
- I added this in the package.json: `proxy": "http://localhost:8080` to avoid Cross origin errors so react will proxy requests to this server through the development server.


findFood(name) {
return fetch(`/api/food/search?name=${name}`)
.then(response => response.json());
}


Actions Change

was:


export const SEARCH_FOOD = 'SEARCH_FOOD';
export function searchFood(term) {
 console.log(`in searchFood ${term}`);
 return {
  type: SEARCH_FOOD,
  term
 }
}


Let's change our actions to make an async call, we need two actions  :
- one to declare the call has started (so components can render loading spinner for example)
- another one to handle the result of the call
we already have SEARCH_FOOD action but now, it will now be used to:
- notify the reducers that the call started instead
to send the ajax call we will introduce a new function (fetchFood) that will:
- invoke the ajax call and host the logic to handle the promise result
- dispatch SEARCH_FOOD
the way we will handle the ajax call result is by dispatching a new action with the result as payload:
 RECEIVE_SEARCH_FOOD_RESULTS
after changes:

Reducers

modifed my reducers as well:
- if the action is SEARCH_FOOD it will set a flag that we are fetching data
- if the action is RECEIVE_SEARCH_FOOD_RESULTS, we will handle the results for that term, and update the state with the results array and unset the fetching flag.

what changes on the component side?

Previously in FoodSearch.js we dispatched the searchFood() action creator result (what builds SEARCH_FOOD action payload )
- the dispatch(searchFood(term)) will change now to dispatch(fetchFood(term))
- this new action creator returns a function that takes dispatch as parameter (to use it later on)

but as we said earlier: the store doesn't understand function actions by default and if you run the app now you will get this error message
Error: Actions must be plain objects. Use custom middleware for async actions.
so we will:
- install redux-thunk run npm install --save redux-thunk
- modify our store creation logic:

import thunkMiddleware from 'redux-thunk';
// lines omitted...
const store = createStore(rootReducer, applyMiddleware(thunkMiddleware));


- running the code will show results from server.

Source for day 3: https://github.com/blabadi/react-nutracker/tree/day3/async-api-call
references: https://redux.js.org/advanced/asyncactions

[ Part 2 ] Nutracker, ReactJS application - Adding Redux

In the first part we covered how to create components and
how to interact with a mock api to get data for our application.

all of that can be enough to build a react app but it won't scale well
for the following reasons:
1- state will be all over the place  in different container components which means we have to add more layers of components to share common parts of states.
2- the propagation of events can be hard to deal with when the components tree gets deeper and other components (siblings and their children) will probably need to be notified of state changes.

Redux data flow

so there is a library called redux, and redux-react.

this library in simple terms facilitates dispatching application wide events to specific handlers (reducers) that modify the state based on the actions they receive, it then store the whole state after those handlers change it and pass the new state to react framework to rerender our components.
In short: it's an event publish/subscriber tailored to manage a state object.

it worth mentioning that redux itself can be used to manage any state, not only react (state is just a JS object at the end of the day) but redux-react adds helper functions and saves you from writing some boilerplate code that we will see soon.

Part 2 code 

https://github.com/blabadi/react-nutracker/tree/01f265a10363a73f359e45db917306be0e1d6efc

Directories added (to organize but not needed):
- actions
- reducers
Renamed:
components => presentational (not related nor needed to redux)

To think the redux way, we have to look at what our component raise for events
currently we have searchBox on term change, this can be translated to a redux 'action' called SEARCH_FOOD.
Actions have to be objects (by default) and to distinguish each action, we give it a type property which is unique string across the app, they also hold any other properties as needed.
So we want our searchBox to send (dispatch in redux terms) a SEARCH_FOOD action to trigger a call to the mock api and fetch foods that match the user query.

Note that our presentation component (SearchBox) won't change in anyway because it was designed not to need so (see part 1 for details).
 Only our container components will change 
from:
 - managing state locally 
 - being responsible to fetch the data by calling the external api (handle events)
to: 
dispatch actions and receive new state

for the first action it will look like this:

the action is just an object, the function that creates that object is called an action creator.
in our case, it takes term as an argument and returns a simple object .
the SearchBox dispatches that action by using the method: dispatch passed to it from redux store
A lot has changed in this component it no longer has any of the react related code, and the reason is:
that it is now created for us by redux using the connect() helper method from redux-react library.
 
The moment you start using redux our container components become unnecessary to be created manually (repetitive boilerplate code) as they will just have one variant in the code , which is to tell redux what to dispatch on each event (mapDispatchToProps), and how to read the state and pass it to child presentation components (mapStateToProps).

without using the connect utility method we will need something like this

class FoodSearchBox extends Component {
  onTermChange = (term) => {
    store.dispatch(searchFood(term))
  }
  render = () => {
     return <SearchBox  ...
            onTermChange = {this.onTermChange}
            results={toResults(store.getState().searchFoodResults)} />

  }
}

The next question if you look at the code above is where did state.searchFoodResults was created ?
the answer is: in the reducer.

A Reducer is a function that receives (state & action) and returns a new state calculated from the action.

for our case here this is our reducer:



it took the state and if the action is SEARCH_FOOD we filled the state with the mock data.
and returned the new state.

few notes:
- Reducers has to be pure functions (no api calls, no database calls nothing that is not a pure js objects manipulation), in this example I did call foodRepo in the reducer but that's just because it's mock data call, not actual network call, but we will change this next part.
- combineReducers is a method from redux that you pass it all the reducers you have and it will build the state tree out of these. (it's good practice to split reducers based on parts of the state each handles, and not have one gigantic function). if we say want to store user information in the state, we would do so by having a reducer like this :
const user = (state = {}, action) => { ... }
and our state will look like this:

{ 
  user: {}, 
  searchFoodResults: [] 
}

and so on, Redux will use the keys (in combineReducers) to build the state and it will also pass that part of the state to that reducer to let it focus on that part of the state so our user reducer will only get a reference to: state.user and not a reference to the whole state tree.

So by now our app hasn't changed functionality wise, but internally it changed a lot, and this is a needed foundation to scale it for a bigger state and more interactions across components.

In the next part I'll explain how we can get rid of the mock data and do an actual async ajax call to an api that will return foods and what will need to change to handle the asynchronous  call.

for more details:
https://redux.js.org/basics/

[ Part 1] Nutracker, ReactJS application - Creation & first component

Part 1: from scratch

Read the introduction

in this part I'll be explaining the first commit, source code for that can be found here:
https://github.com/blabadi/react-nutracker/tree/f3b998b6e4ba9d2cdeed15ce637066fac0647c1f

Creating the project:

run this command (this is using nodeJS binary) :
npx create-react-app react-nutracker

this will initialize the directories and we are ready to start adding our code.
this is a command line tool created by react team to make initializing as easy as possible because it can be overwhelming for people to configure everything, let's focus on react for now and not the details that can be done later.
see: https://github.com/facebook/create-react-app

you can also start the application and it will work:
npm start

Install bootstrap

npm install --save bootstrap

import bootstrap in the index.js file.
import 'bootstrap/dist/css/bootstrap.min.css';

The First NUtracker Component: Search box

1-  I added the following directories:  components, containers, repos, model


2- in component/search the initial version of SearchBox component:

and used here in Dashboard Component:

Observations:

• The dashboard component stores the results in the state
• It passes to the searchBox what to do when the user enters a new search term (onTermChange callback)
• It also passes the results of the search for the search box to render AFTER fetching the results from the food repo (mock for a call to food REST api). the reason to have this kind of design is to keep search box a dumb component that can be reused again without it being aware of how to get the results. it's only a presentation component (i.e. it just renders html and notifies its container of any user events it receives)
• The dashboard is a container component, which means it manages one or many presentation components and provide them with the props they need to function either from server or whatever, and it also manages what to do when an event is raised by the child components, in this example it calls foodRepo to get foods based on what the user has input in the box.
• Note that when we get the results from food repo we store them in the state in a key value generic properties, to allow the search box to render the results without knowing what kind of results it is, it could be foods, articles, cats, whatever.
• Also the key is needed by react when you render a list of anything or you will get an error, a property called key is needed in the html elements for react to work.
• foodRepo and model is something I preferred to do, but you can organize the way you want.

result after part 1:



Part two: Adding Redux. : http://dev.basharallabadi.com/2018/09/part-2-nutracker-reactjs-application.html

[ Intro ] Nutracker, ReactJS application Step By Step

I worked before on learning angular 2+, and made a sample functioning app that tracks calories &  macros, called it NUtracker.


For live running version (angular) : here. (buggy as it's just prototype, after registration set your profile goals first otherwise it will look broken).

Main functionalities:

- search for foods from a db
- add new food to the db
- add them as daily entries
- calculate the total daily intake of calories, carbs, fats & protein with respect to the daily goals
- users can set the goals in their profile screen.
- login/registration screen.
- move back and to see other days entries.
- edit/remove entries

Why?

in this series of blogs I'll try to replicate this angular project in react, for two reasons:
1- get a sense of both framework and compare them to each other apple to apple.
2- apply what I learn about react & it's eco-system in a project and solve the problems I face.

The main goal of this blogs series is

To document how an app starts and evolves overtime and how to handle real case needs step by step*

* by step-by-step i don't mean line by line of code, but rather steps in the project and adding functionalities, so each part I'll be talking about a commit or two that aimed to fulfill a need or implement a specific functionality while trying to be focused on new things and not repeating, so you will need to figure out some details. I won't suggest following my exact example but rather build your own app wit this as an example of how and what to expect.

Learn React

I mainly learned react (serious learning) from this book: Full Stack React
the good thing about books is that you get a good foundation and intuition of  how things work and why in more details than other sources, However, you can learn reactJS basics anywhere in 1 hour or so which can be enough to follow this series.

Prerequisites:

- you know html , css, javascript ES6+, bootstrap
- you know what npm is and what package.json and got NodeJS installed.
- you know what reactJS is as framework and the basic concepts (state, props, reactivity, render( ), JSX, components) but didn't necessarily worked with react in a project.

Repository

https://github.com/blabadi/react-nutracker

Series Parts

• Part1: Creating the project and adding the first component.
• Part 2: Adding redux foundation.
• Part 3: Adding the first async call action by using redux-thunk middleware.

PART 2 [Front end] - Docker for Angular + Spring Boot

this the second part of dockerizing an angular 6 and spring boot app

Part 1 here: http://dev.basharallabadi.com/2018/08/part-1-backend-docker-for-angular.html

I followed this blog:
https://mherman.org/blog/2018/02/26/dockerizing-an-angular-app/

so basically three steps:

1- create docker file
2- create docker compose
3- docker-compose build .. docker-compose up

here is the files I'll be explaining to achive this:
.

1- Dockerfile
This docker file uses multi stage build, which means it uses multiple docker images to produce final image.

why?

because the image we need to build the angular app requires alot of dependencies that are not needed to run the app.

in the first part of the docker file:
- it starts based on a node image
- prepares the app directory
- copies package.json from the source code directory to the docker container directory
- executes npm install which will install all node dependencies.
- install angular cli globally (version 6)
- copy everything from the root directory to the 'app' directory we created before
- execute ng build to get the compiled app code that will be served by a web server
  note that for this step I'm specifying the build environment, which is passed as an arg to the dockerfile
 this command used to be : ng build --env=$build_env .. but in angular 6 got changed.

The reason we build the app is because the ng serve is good for local  development use only.
it's not good and it didn't seem to work to accept remote requests over the network
and in my case I wanted to use docker to make it faster to deploy the app on different environments not to develop there so I went with the choice to build the app.
The reason I pass the environment is to specify for angular which environment.ts file to be used because I wanted to be able to debug this build if needed, and not have production build where it's harder to debug.

2nd part / stage :
-we start off an official nginx image
-copy the output from first image build to the html directory of nginx container (the path for the html directory is provided by the image itself)
- copy our custom nginx configs to overwrite default configs
[ the reason for this is to proxy our api calls from angular through nginx to the boot REST api container to avoid allowing CORS (Cross Origin Requests).. note that I used the IP of the instance to get the requests to the boot container on port 8080 ]
- expose port 8008 from this container to the outer world network
- start nginx 


Things worth noting:
* while building the angular app it was throwing disk out of space error.. this is due to the huge size of the node_modules directory, and because docker doesn't clean up images between part 1 & 2

so to avoid any issues make sure to clean up the unused docker artifacts before/after the image build:
- docker system prune -a -f
- docker volume ls -qf dangling=true | xargs -r docker volume rm;

PART 1 [Backend] - Docker for Angular + Spring Boot

I have been working on an angular 4 (upgraded to 6) application backed by spring boot rest api, repositories:
1- api: https://github.com/blabadi/nutracker-api
2- angular: https://github.com/blabadi/nutritionTracker

and this post is about using and adding docker to these apps to make it easier to deploy and share.

Disclaimer: this is not by any means a best practice article, but was more of a hands on way to learn more about Docker work flow and challenges that one may face.

Part 1: Dockerizing the backend project (nutracker-api)

I was testing this process on amazon micro instance and these are the steps I followed:

pre requisite:
- install docker on aws:
https://docs.aws.amazon.com/AmazonECS/latest/developerguide/docker-basics.html

1- add docker file (point to a built jar for now)

reference: https://www.callicoder.com/spring-boot-docker-example/

this docker file is simple
it:
- gets a jdk image
- copies our pre built jar from the build output directory
- starts the jar (which is a spring boot jar that starts an embedded web server)

to understand the details of the docker file contents, see:
reference: https://spring.io/guides/gs/spring-boot-docker/

2- install docker compose

https://magescale.com/installing-docker-docker-compose-on-aws-linux-ami/
Docker compose helps in building and running multiple containers in one command
so in my case I needed to run my spring boot jar and have it connected to a mongo db instance (also hosted in docker container)

3- add docker-compose to include mongo db

https://medium.com/statuscode/dockerising-a-node-js-and-mongodb-app-d22047e2806f

this  in the following order :
1- prepares and runs a container for mongo by using the mongo image
2- mount a real path to the container path  to persist the db data.
3- builds a container from a Dockerfile located in the same directory.
4- expose this api on container port: 8080

note that we pass the mongo container name as environment variable to the api container, which uses that variable to configure the mongo client (MongoConfig.java)

you may find people adding a 'link' key to the docker compose (or when they run the container).
 http://www.littlebigextra.com/how-to-connect-to-spring-boot-rest-service-to-mongo-db-in-docker/

but that is an older way to do it. in my example I'm utilizing the docker network created by default when you run a compose file and in that case you can connect to containers by their name out of the box
https://dev-pages.info/how-to-run-spring-boot-and-mongodb-in-docker-container/

so in summary for the backend project I did:

1- create docker file to run the spring boot based on a jdk image
2- create a docker compose to spin a mongo container and run the Dockerfile from step 1
3- run the commands in following sequence:
   a) build the jar (the -x to not execute): ./gradlew build -x test
   b) docker-compose build, builds the images
   c) docker-compose up, runs the containers

the three steps above is what you do in case you change your code and want to re/deploy it somewhere.

seems straight forward but i faced few issues to boil down to these and learn my mistakes.

Notes/hints related to this part:

- to stop all docker containers running:
docker stop $(docker ps -a -q)

- docker-compose up :
doesn't rebuild the containers (in case you change code or Dockerfile), if you change something in the jar, it won't update automatically

- docker-compose build :
 rebuilds our java app image (nutracker-api) boot application

- to access the api from browser/rest client remotely I had to use :

expose:
 - <port>

in docker-compose.
using:

 ports:
  - port1:port2

was not enough to publicly access the docker containers but can be enough for local communications of containers on same docker network.

- There is a gradle & maven plugin to automate the docker image build & push to docker hub as part of your build steps which is more practical solution.
and saves you from having to build the code at the host machine as I had to do. i just opted-out from doing it to keep things simple 
https://www.callicoder.com/spring-boot-docker-example/#automating-the-docker-image-creation-and-publishing-using-dockerfile-maven-plugin


Part 2: Dockerizing the Angular app will follow in the next blog post

Setting up TensorFlow backed Keras with GPU in Anaconda - Windows

I wanted to use my GPU instead of CPU in Keras, after knowing that it supports CUDA, for a simple deep learning example training, so I had to do some search on how to set it up and ended with this summary:
 
Pre requisites :
1- Anaconda installed
2- setup Nividia CUDA 9.0 https://developer.nvidia.com/cuda-90-download-archive
3- setup Nividia cuDNN 7 (for CUDA 9.0) https://developer.nvidia.com/rdp/cudnn-download
https://docs.nvidia.com/deeplearning/sdk/cudnn-install/index.html#install-windows

Steps:

0) run Anaconda Prompt

1) install conda packages
conda create --name tf-gpu-keras-p35 python=3.5 pip
activate tf-gpu-keras-p35
conda install jupyter
conda install scipy
conda install scikit-learn
conda install pandas
pip install tensorflow-gpu
pip install keras

The following didn't work for me:
(didn't work with keras, keras installed tensorflow 1.1.0) keras keeps overriding the tensorflow-gpu
you get empty tensorflow module
conda install -c conda-forge keras
conda install -c conda-forge keras-gpu
conda install -c conda-forge tensorflow
conda install -c anaconda tensorflow-gpu

2) Set keras to use tensorflow backend, in case it uses theano (default)

go to Anaconda3/envs/<env name>/etc/activate.d/keras_activate.bat
go to <User home directory>\.keras\keras.json and change to tensorflow

3) run jupyter:
jupyter notebook

Hibernate Objects,Sessions across threads - Illegal attempt to associate a collection with two open sessions

In the land of Hibernate a concept of Session is important.
it plays the role of tracking changes that happen to (hibernate objects) from the moment you open it.
and you can't actually do much without it, it's your entry to hibernate capabilities

so if you want to load an object you have to obtain a session instance first then load the object:

Session s = sessionFactory.getCurrentSession();
MyObject mo = s.byId(MyObject.class).load(123);

now that object (mo) is associated with that session
if you do something like

mo.setName('new Name');


the session will track that this object is dirty. and it does much more that you can read about.

What I want to get to is that in case you have to do some background work with your object you have to be careful that:
1- the session is not thread safe (i.e. it can't be passed between threads and assume no concurrency issues will happen)
2- the objects associated with one session cannot be associated with another open session

so if you try to do something like this:

// this is psudo code, just to get the point:\
MyObject mo = dao.load(123);
new Thread( () -> {
     mo.setName('abc');
     dao.update(mo);
}).run();

// Data access methods (usually in a dao)
MyObject load(int id) {
  return   sessionFactory.getCurrentSession().byId(MyObject.class).load(123);
}

void update(MyObject m) {
   Session s = sessionFactory.getCurrentSession();
   s.save(m);
}

that won't work, and hibernate will complain :

Illegal attempt to associate a collection with two open sessions

because we passed the object between two threads while the first session could still be open when the second other thread starts.

and what makes it worse is that you probably won't see the exception message because the other thread won't stop your main thread execution and you will never know why the update failed.

so as a good practice is to have good error handling in background threads.

I had to learn this the hard way after debugging something similar where my update had to be done in background and spent few hours debugging a ghost issue without clue until I placed some std out /err good old print statements because debugging multiple threads can be hard when there is alot of moving parts.

Solution:

1- don't pass hibernate object

2- pass the id of the object instead / or anything to reload it fast in the other thread, that way it will not be considered the same object.
 

// transaction A

MyObject mo = dao.load(123); <-- will work in session 1
//do stuff with mo

new Thread( () -> {
     // transaction B
     // reload the hibernate object and don't use the one from other thread
     MyObject mo2 = dao.load(123); <-- this will be associated with session 2

     mo2.setName('abc');
     dao.update(mo2);
}).run();

another solutions involve using evict(); and merge(); 

Cheers !

read more:
1- https://developer.jboss.org/wiki/Sessionsandtransactions?_sscc=t
2-https://stackoverflow.com/questions/11673303/multithread-hibernateexception-illegal-attempt-to-associate-a-collection-with
3- https://stackoverflow.com/questions/11237924/hibernate-multi-thread-multi-session-and-objects