Flow Database Access CorDapp

This CorDapp provides a simple example of how the node database can be accessed in flows. In this case, the flows maintain a table of cryptocurrency values in the node's database. There are three flows:

The CorDapp defines three flows:

• AddTokenValueFlow, which adds a new token to the database table with an initial value
• UpdateTokenValueFlow, which updates the value of an existing token in the database table
• QueryTokenValueFlow, which reads the value of an existing token from the database table

Under the hood, the database accesses are 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:

See https://docs.corda.net/getting-set-up.html.

Usage

Running the nodes:

See https://docs.corda.net/tutorial-cordapp.html#running-the-example-cordapp.

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

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

start UpdateTokenValueFlow token: "mango_coin", value: 500

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

start QueryTokenValueFlow token: "mango_coin"