Description

This a simplistic Dockerized Spring Boot app for testing hierarchical data retrieval (and other operations) with MongoDB. Created for the purposes of the DZone article https://dzone.com/articles/manage-hierarchical-data-in-mongodb-with-spring.

References

In order to be able to follow-up better the reasoning, check the following stuff:

• https://docs.mongodb.com/manual/applications/data-models-tree-structures/
• https://www.slideshare.net/mongodb/webinar-working-with-graph-data-in-mongodb
• https://docs.mongodb.com/manual/reference/operator/aggregation/graphLookup/

Prerequisites

In order to execute the app:

• Install Docker and Docker Compose 🐳

In order to build, test etc:

• Apache Maven 3.5.x and above
• Java 11 and above

Usage

Sample data is provided (see nodes.json). The data are like a "forest of trees" i.e. multiple trees under a "virtual root" node with id (nodeId) having the value "-1". Each tree is identified by its treeId and each node by is nodeId.

Endpoints

Method	Path	Description
GET	/app/{treeId}	retrieve a whole hierarchical structure by treeId
GET	/app/{treeId}/set/{nodeId}	retrieve a sub-tree of a treeId, starting from the node with a given nodeId
POST	under development	add a new node to a given tree (arbitrary depth)
PUT	under development	update an existing node
DELETE	under development	delete a node
GET	under development	compare subtrees with Javers

You can have a view of a whole tree from the imported tree-structure by performing an HTTP-GET operation:

• http://localhost:8080/app/1001

Then you may retrieve sub-trees by performing am HTTP-GET operation on the following URL:

• http://localhost:8080/app/1001/st/100

How to run

You can try this app with the following 2 ways:

• by spinning a MongoDB cluster with docker-compose.yml and run the Spring-boot app standalone (non-dockerized)
• by using docker-compose-all.yml and bring up both the MongoDB cluster and the app all-together (dockerized)

Allow cluster connectivity

This step is necessary if you want to run the Spring-boot app standalone and/or to be able to execute Integration tests.

Modify your /etc/hosts file and add the following 3 entries:

• 127.0.0.1 mongo1
• 127.0.0.1 mongo2
• 127.0.0.1 mongo3

Build/Test

First of all you need to build the app with:

mvn clean build

If you want to execute Integration tests, go with:

mvn verify

With the help of docker-compose-maven-plugin this will start a MongoDB replica set and then the integration tests will be executed.

Run the Spring-boot app non-dockerized

Bring up the MongoDB cluster with:

docker-compose up

Run the application with:

mvn spring-boot:run

Run the Spring-boot app dockerized

Alternatively, if you want to start everything with docker-compose, execute the following:

mvn clean package
docker-compose -f docker-compose-all.yml build
docker-compose -f docker-compose-all.yml up

Load sample data

Once the cluster is up, load the sample data, with:

docker-compose exec mongo1 mongoimport --host mongo1 --db test --collection nodes --type json --file /tmp/nodes.json --jsonArray

To bring down all the containers, execute:

docker-compose down -v --remove-orphans

This way the containers are disposed and cleanup is performed.

Additional information

$graphLookup example

You can try this via Mongo Shell:

db.nodes.aggregate([ 
{ $match: { treeId: 1001, $and: [ { nodeId: 100 } ] } },
{
 $graphLookup: {
    from: "nodes",
    startWith: "$nodeId",
    connectFromField: "nodeId",
    connectToField: "parentId",
    restrictSearchWithMatch: {"treeId": 1001},
    as: "descendants"
 }
}
]);

Schema indexes

Indexes on the following fields (based on the sample data) are necessary for achieving performance:

• nodeId
• treeId
• parentId