10.Neo4j

Workshop 10 - Discover graph database with Neo4j

✔️ Learn graph database concept

✔️ Interact with a graph database

✔️ Use an OGM to simplify your development

✔️ Understand Cypher syntax

✔️ Build basics query through a query builder

✔️ Test your Typescript code with Jest framework

Step 0 - Initialization

All the required information to start this workshop can be found in SETUP.md.

Story

A group of publishing houses wants to build a search engine so that their customers can easily find the nearest publishing house selling the book they are looking for.

You have been assigned to the development of the back-end and more specifically, the "data storage and management" part. Your mission is to develop functions to interact with the data stored in a database.

The stored data follow the following scheme:

To store data, several solutions are available to you. First, the use of a relational database, classic but efficient, this system has proven itself for several years and has been adopted by many companies.
But there are also graph databases, also very old but not very popular, these have remained rather discreet, the community is smaller, the tools less popular but just as effective.

Not knowing what to choose, you ask your supervisor for advice, who asks you the following question:
do your data have close relationships between them, are you going to use these relationships in a recurring way ?

The answer is of course yes ! A book must always be linked to its author and its sales points, otherwise the platform would be useless.

So you decide to store your data in a graph database. It's time to move on to development, let's go for the discovery of graph databases with Neo4j and its Typescript OGM : Neogma.

Step 1 - Did you say database?

Database

Our objective is to store data... Wait, where is our database?

Hmm yes, we must run a database to work with! Let's launch neo4j database thanks docker.

docker run -d --name workshop-poc-neo4j -p 7474:7474 -p 7687:7687 -e NEO4J_AUTH=$NEO4J_USER/$NEO4J_PASSWORD neo4j

⚠️ You must load your environment to make this commands work !

💡 If you don't understand the command, check docker run options

The container expose:

• The graphic interface on port 7474, you can go it through this link.
• The bolt on port 7687, you can use it to send request from your code.

Now, we must create a connection directly in the code to communicate with our database.

Connection

We will use an OGM to simplify our interaction, let's use Neogma a complete typed OGM for Neo4j.

• Tip npm install neogma to install the dependency in your project.
• Create a file named appDatabase.ts in the src folder.
• In this file, use Neogma to export a database client connected to your database.

💡 You should use the dbConfig variable to authenticate your client to your database.

Take a look at the documentation to learn how set up a client.

Check models

To verify that your connection is working, modify the file index.ts to print models defined in the database.

It should print an empty object like this:

> [email protected] dev
> ts-node src/index.ts

{}

Good job, the database is ready to store some data !

💡 You should take a look at this link to see some helpers about models.

Step 2 - Books

Let's store the main entity of our schema: books.

First, create a directory entities in the directory src to store all our entities management functions.

Now, inside this directory, let's create another directory named Books.

Entity

Create a file named BooksEntity.ts and define your entity properties in.

To do that:

• Create a type BooksPropertiesI which define all your fields and their type according to the previous schema.

💡 You must add a property id of type string to recognize books that has common values.

• Create an empty interface named BooksRelationNodesI to store all your relation, we will fill it later.
• Create a type BooksInstance, which will be equal to the generic type NeogmaInstance, filled with the types we previously defined.

Your types are defined, let's create the node:

Export a const variable named Books. It is equal to the result of the function ModelFactory, which create a new model using the types we previously defined, and some additional information we give in the parameters. The ModelFactory function takes an object which must contain the following fields:

• label: the name we choose for the Model, here it's Book.
• primaryKeyField: primary key use to recognize entity, here it's id.
• schema: defines the data of the model, and applies some constraints to enforce some data safety.

⚠️ Don't forget to pass the neogma client as the second argument !

💡 You should take a look at this link to get some examples of entity definition.

Function

Let's develop some functions to interact with our entity. It's common to add elementary CRUD functions when you create an entity.

💡 Be careful, those operations are asynchronous ! Don't forget to use async and await keywords. You can check this documentation for more information.

You must write those function in a file named BooksModels in the entities/Books folder.

Create

• Create a function createBook which takes book properties as parameters expect the id and create a new book in the database.

💡 You should generate a unique id with the uuid npm package.

The create function return a BooksInstance, you should create a utility function to convert it to BooksPropertiesI.

Read

• Create a function getBooks which takes no parameters and return an array of books stored in the database.
• Create a function getBook that takes an id as parameter and return the book which add the id equal to the parameter or null if the id is not found.

Update

• Create a function updateBook which takes as parameters:
  • id: book id
  • bookProperties: all properties to update, this parameter must be of type Partial<BooksPropertiesI> to make the all properties optional. Like this, we can update on or more values without problem.

This function must return the updated book.

💡 Take your time to understand what is the return type of the update function provide by the Books factory.

Delete

• Create a function deleteBook which takes as parameter an id and return nothing.

⚠️ A deleted node must also close all his relation.

Tests

You can add the books.tests.ts file from the tests folder of that repository to test your work.

Step 3 - Authors?

We can store books, it's cool ! But authors should be awarded for their work no ?

Models

Let's add a new entity named Authors in the entities folder.

Repeat the same process from step 1 to interact with this new entity.

💡 You can do it very fast because the only things that changes are properties of the entity, the management functions should be the same

Tests

You can add the authors.tests.ts file from the tests folder of that repository to test your work.

Step 4 - Who's authors

Now, we got books and authors... Let's link them with a simple relation.

In graph database, relations can be represented like human relation. For example: authors wrote those books.

Modify the BooksEntity.ts file to add the relation WriteBy in your book.

• Add the relationship Author in the BooksRelationNodeI interface.
• Add the relationship Author in the Books factory.

💡 Take a look at this documentation to understand how add relation in your factory.

Function

Create the BooksRelations.ts file and develop three important function:

⚠️ This step is very hard and need some research to finish it. Take your time.

• linkBookToAuthor which takes as parameters:
  • bookId: Book id
  • authorId: Author id This function should create the relation WriteBy between the book and the author and return the book with the author.

You can use the relateTo function to create the relation, however, you'll need to create your own query thanks to the QueryBuilder class. You will need an queryRunner instance, you can create a file appDbInstance to store it in.

• getAuthorBooks which takes as parameters an id and return the author with all books that he wrote.

You will need to create a utility function that convert the query result into a readable object.

💡 You can create type in the BookEntity.ts file. Don't store it in AuthorEntity.ts to avoid circle dependencies problem.

• detachBookFromAuthor which takes as parameters:
  • bookId: Book id
  • authorId: Author id This function should delete the relation WriteBy between the book and the author and return true if the operation works, false if it failed.

Tests 🧪

You can add the books-authors.tests.ts file from the tests folder of that repository to test your work.

💡 You can also use the tests to use the complete test suite of the workshop.

⚠️ You will the to modify the jest.config.js and replace testMatch field with testMatch: ['**/tests/index.ts'],

Bonus

You learnt how to use neogma and Neo4j! Congratulation 🔥

Now, you can complete your work by implementing others entities.

Remember that schema:

Authors

Tom Chauveau

Organization

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