Create a Sample Application That Uses ScalarDB

This tutorial describes how to create a sample e-commerce application by using ScalarDB.

Overview

The sample e-commerce application shows how users can order and pay for items by using a line of credit.

The database that you will be using in the sample application is Cassandra. Although Cassandra does not provide ACID transaction capabilities, you can make transactions ACID compliant by having your application connect to the database through ScalarDB.

To reference the sample application source code, see src/main/java/sample/Sample.java.

Note

Since the focus of the sample application is to demonstrate using ScalarDB, application-specific error handling, authentication processing, and similar functions are not included in the sample application. For details about exception handling in ScalarDB, see Handle exceptions.

What you can do in this sample application

The sample application supports the following types of transactions:

Get customer information.
Place an order by using a line of credit.
- Checks if the cost of the order is below the customer’s credit limit.
- If the check passes, records the order history and updates the amount the customer has spent.
Get order information by order ID.
Get order information by customer ID.
Make a payment.
- Reduces the amount the customer has spent.

Prerequisites

One of the following Java Development Kits (JDKs):
- Oracle JDK LTS version (8, 11, or 17)
- OpenJDK LTS version (8, 11, or 17)
Docker 20.10 or later with Docker Compose V2 or later

Note

We recommend using the LTS versions mentioned above, but other non-LTS versions may work.

In addition, other JDKs should work with ScalarDB, but we haven’t tested them.

Set up ScalarDB

The following sections describe how to set up the sample e-commerce application.

Clone the ScalarDB samples repository

Open Terminal, then clone the ScalarDB samples repository by running the following command:

$ git clone https://github.com/scalar-labs/scalardb-samples

Then, go to the directory that contains the sample application by running the following command:

$ cd scalardb-samples/scalardb-sample

Start Cassandra

Cassandra is already configured for the sample application, as shown in database.properties.

To start Cassandra, which is included in the Docker container for the sample application, make sure Docker is running and then run the following command:

$ docker-compose up -d

Note

Starting the Docker container may take more than one minute depending on your development environment.

Load the schema

The database schema (the method in which the data will be organized) for the sample application has already been defined in schema.json.

To apply the schema, go to the ScalarDB Releases page and download the ScalarDB Schema Loader that matches the version of ScalarDB that you want to use to the scalardb-samples/scalardb-sample folder.

Then, run the following command, replacing <VERSION> with the version of the ScalarDB Schema Loader that you downloaded:

$ java -jar scalardb-schema-loader-<VERSION>.jar --config database.properties --schema-file schema.json --coordinator

Schema details

As shown in schema.json for the sample application, all the tables are created in the sample namespace.

sample.customers: a table that manages customer information
- credit_limit: the maximum amount of money that the lender will allow the customer to spend from their line of credit
- credit_total: the amount of money that the customer has spent from their line of credit
sample.orders: a table that manages order information
sample.statements: a table that manages order statement information
sample.items: a table that manages information for items to be ordered

The Entity Relationship Diagram for the schema is as follows:

ERD

Load the initial data

After the Docker container has started, load the initial data by running the following command:

$ ./gradlew run --args="LoadInitialData"

After the initial data has loaded, the following records should be stored in the tables.

sample.customers table

customer_id	name	credit_limit
1	Yamada Taro	10000
2	Yamada Hanako	10000
3	Suzuki Ichiro	10000

sample.items table

item_id	name	price
1	Apple	1000
2	Orange	2000
3	Grape	2500
4	Mango	5000
5	Melon	3000

Execute transactions and retrieve data in the sample application

The following sections describe how to execute transactions and retrieve data in the sample e-commerce application.

Get customer information

Start with getting information about the customer whose ID is 1 by running the following command:

$ ./gradlew run --args="GetCustomerInfo 1"

You should see the following output:

...
{"id": 1, "name": "Yamada Taro", "credit_limit": 10000, "credit_total": 0}
...

Place an order

Then, have customer ID 1 place an order for three apples and two oranges by running the following command:

Note

The order format in this command is ./gradlew run --args="PlaceOrder <CUSTOMER_ID> <ITEM_ID>:<COUNT>,<ITEM_ID>:<COUNT>,...".

$ ./gradlew run --args="PlaceOrder 1 1:3,2:2"

You should see a similar output as below, with a different UUID for order_id, which confirms that the order was successful:

...
{"order_id": "dea4964a-ff50-4ecf-9201-027981a1566e"}
...

Check order details

Check details about the order by running the following command, replacing <ORDER_ID_UUID> with the UUID for the order_id that was shown after running the previous command:

$ ./gradlew run --args="GetOrder <ORDER_ID_UUID>"

You should see a similar output as below, with different UUIDs for order_id and timestamp:

...
{"order": {"order_id": "dea4964a-ff50-4ecf-9201-027981a1566e","timestamp": 1650948340914,"customer_id": 1,"customer_name": "Yamada Taro","statement": [{"item_id": 1,"item_name": "Apple","price": 1000,"count": 3,"total": 3000},{"item_id": 2,"item_name": "Orange","price": 2000,"count": 2,"total": 4000}],"total": 7000}}
...

Place another order

Place an order for one melon that uses the remaining amount in credit_total for customer ID 1 by running the following command:

$ ./gradlew run --args="PlaceOrder 1 5:1"

You should see a similar output as below, with a different UUID for order_id, which confirms that the order was successful:

...
{"order_id": "bcc34150-91fa-4bea-83db-d2dbe6f0f30d"}
...

Check order history

Get the history of all orders for customer ID 1 by running the following command:

$ ./gradlew run --args="GetOrders 1"

You should see a similar output as below, with different UUIDs for order_id and timestamp, which shows the history of all orders for customer ID 1 in descending order by timestamp:

...
{"order": [{"order_id": "dea4964a-ff50-4ecf-9201-027981a1566e","timestamp": 1650948340914,"customer_id": 1,"customer_name": "Yamada Taro","statement": [{"item_id": 1,"item_name": "Apple","price": 1000,"count": 3,"total": 3000},{"item_id": 2,"item_name": "Orange","price": 2000,"count": 2,"total": 4000}],"total": 7000},{"order_id": "bcc34150-91fa-4bea-83db-d2dbe6f0f30d","timestamp": 1650948412766,"customer_id": 1,"customer_name": "Yamada Taro","statement": [{"item_id": 5,"item_name": "Melon","price": 3000,"count": 1,"total": 3000}],"total": 3000}]}
...

Check credit total

Get the credit total for customer ID 1 by running the following command:

$ ./gradlew run --args="GetCustomerInfo 1"

You should see the following output, which shows that customer ID 1 has reached their credit_limit in credit_total and cannot place anymore orders:

...
{"id": 1, "name": "Yamada Taro", "credit_limit": 10000, "credit_total": 10000}
...

Try to place an order for one grape and one mango by running the following command:

$ ./gradlew run --args="PlaceOrder 1 3:1,4:1"

You should see the following output, which shows that the order failed because the credit_total amount would exceed the credit_limit amount.

...
java.lang.RuntimeException: Credit limit exceeded
        at sample.Sample.placeOrder(Sample.java:205)
        at sample.command.PlaceOrderCommand.call(PlaceOrderCommand.java:33)
        at sample.command.PlaceOrderCommand.call(PlaceOrderCommand.java:8)
        at picocli.CommandLine.executeUserObject(CommandLine.java:1783)
        at picocli.CommandLine.access$900(CommandLine.java:145)
        at picocli.CommandLine$RunLast.handle(CommandLine.java:2141)
        at picocli.CommandLine$RunLast.handle(CommandLine.java:2108)
        at picocli.CommandLine$AbstractParseResultHandler.execute(CommandLine.java:1975)
        at picocli.CommandLine.execute(CommandLine.java:1904)
        at sample.command.SampleCommand.main(SampleCommand.java:35)
...

Make a payment

To continue making orders, customer ID 1 must make a payment to reduce the credit_total amount.

Make a payment by running the following command:

$ ./gradlew run --args="Repayment 1 8000"

Then, check the credit_total amount for customer ID 1 by running the following command:

$ ./gradlew run --args="GetCustomerInfo 1"

You should see the following output, which shows that a payment was applied to customer ID 1, reducing the credit_total amount:

...
{"id": 1, "name": "Yamada Taro", "credit_limit": 10000, "credit_total": 2000}
...

Now that customer ID 1 has made a payment, place an order for one grape and one melon by running the following command:

$ ./gradlew run --args="PlaceOrder 1 3:1,4:1"

You should see a similar output as below, with a different UUID for order_id, which confirms that the order was successful:

...
{"order_id": "8911cab3-1c2b-4322-9386-adb1c024e078"}
...

Stop the sample application

To stop the sample application, stop the Docker container by running the following command:

$ docker-compose down