Struct QldbClient

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pub struct QldbClient { /* private fields */ }

Expand description

It allows to start transactions. In QLDB all queries are transactions. So you always need to create a transaction for every query.

The recommended method is transaction_within.

Implementations§

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impl QldbClient

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pub async fn default( ledger_name: &str, max_sessions: u16, ) -> QldbResult<QldbClient>

Creates a new QldbClient.

It will spawn one thread for the session pool.

This function will take the credentials from several locations in this order:

Environment variables: AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY
credential_process command in the AWS config file, usually located at ~/.aws/config.
AWS credentials file. Usually located at ~/.aws/credentials.
IAM instance profile. Will only work if running on an EC2 instance with an instance profile/role.

https://docs.rs/rusoto_credential/0.45.0/rusoto_credential/struct.ChainProvider.html

For the region it will will attempt to read the AWS_DEFAULT_REGION or AWS_REGION environment variable. If it is malformed, it will fall back to Region::UsEast1. If it is not present it will fallback on the value associated with the current profile in ~/.aws/config or the file specified by the AWS_CONFIG_FILE environment variable. If that is malformed of absent it will fall back on Region::UsEast1

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pub async fn default_with_spawner( ledger_name: &str, max_sessions: u16, spawner: Arc<dyn Fn(Pin<Box<dyn Future<Output = ()> + Send>>) + Send + Sync>, ) -> QldbResult<QldbClient>

Creates a new QldbClient.

This function won’t spawn a thread for the session pool, but it will require to be given an spawn function so it can start 2 green threads for the session pool.

This function will take the credentials from several locations in this order:

Environment variables: AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY
credential_process command in the AWS config file, usually located at ~/.aws/config.
AWS credentials file. Usually located at ~/.aws/credentials.
IAM instance profile. Will only work if running on an EC2 instance with an instance profile/role.

https://docs.rs/rusoto_credential/0.45.0/rusoto_credential/struct.ChainProvider.html

For the region it will will attempt to read the AWS_DEFAULT_REGION or AWS_REGION environment variable. If it is malformed, it will fall back to Region::UsEast1. If it is not present it will fallback on the value associated with the current profile in ~/.aws/config or the file specified by the AWS_CONFIG_FILE environment variable. If that is malformed of absent it will fall back on Region::UsEast1

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pub async fn read_query(&self, statement: &str) -> QldbResult<QueryBuilder>

Shorthand method that creates a transaction and executes a query. Currently it doesn’t filter by statements, so any statement can be sent but it won’t have effect as it will rollback any change. This allows to read big quantities of data without failing other transactions that may be reading that data at the same time.

This is a good option when you want to execute an isolated non-ACID SELECT/COUNT statement.

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pub async fn transaction(&self) -> QldbResult<Transaction>

Starts a transaction and returns you the transaction handler. When using this method the transaction won’t automatically commit or rollback when finished. If they are left open they will be canceled when the transaction times out on the DB side (30 seconds).

Use this method if you really need to use the transaction handler directly. If not, you may be better off using the method transaction_within.

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pub async fn close(&mut self)

It closes the session pool. Current transaction which already have a session can work as normal, but new transaction (requiring a new session id) will return error.

Call this method only when you are sure that all important work is already commited to QLDB.

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