flow-database-access

Flow Database Access CorDapp

This CorDapp provides a simple example of how the node database can be accessed in flows using a JDBC Connection. In this case, the flows maintain a table of cryptocurrency values in the node's database.

Concepts

Flows

The CorDapp defines three flows: AddTokenValueFlow, UpdateTokenValueFlow, and QueryTokenValueFlow. Under the hood, database access is managed by the CryptoValuesDatabaseService CordaService.

Be aware that support of database accesses in flows is currently limited:

• The operation must be executed in a BLOCKING way. Flows don't currently support suspending to await an operation's response
• The operation must be idempotent. If the flow fails and has to restart from a checkpoint, the operation will also be replayed

Pre-Requisites

For development environment setup, please refer to: Setup Guide.

Running the nodes

Open a terminal and go to the project root directory and type: (to deploy the nodes using bootstrapper)

./gradlew clean deployNodes

Then type: (to run the nodes)

./build/nodes/runnodes

Interacting with the node:

We'll be interacting with the node via its interactive shell.

Suppose we want to add a token called mango_coin to the node's database table with an initial value of 100. In the node's interactive shell, run the following command:

start AddTokenValueFlow token: "mango_coin", value: 100

And read back mango_coin's value from the node's database table by running:

start QueryTokenValueFlow token: "mango_coin"

We can then update mango_coin's value to 500 by running:

start UpdateTokenValueFlow token: "mango_coin", value: 500

Again read back mango_coin's value from the node's database table by running:

start QueryTokenValueFlow token: "mango_coin"