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Schema¶
The driver is capable of fetching database schema and presenting it to its users.
Fetching schema¶
Fetching database schema occurs periodically, but it can also be done on-demand. In order to fetch the newest database schema, one can call refresh_metadata() on a Session instance:
#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
let uri = std::env::var("SCYLLA_URI")
.unwrap_or_else(|_| "127.0.0.1:9042".to_string());
let session: Session = SessionBuilder::new().known_node(uri).build().await?;
// Schema metadata will be fetched below
session.refresh_metadata().await?;
Ok(())
}
Inspecting schema¶
Once fetched, a snapshot of cluster’s schema can be examined. The following information can be obtained:
keyspace
tables belonging to the keyspace
materialized views belonging to the keyspace
replication strategy
user-defined types
table/view
primary key definition
columns
partitioner type
Example showing how to print obtained schema information:
#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
let uri = std::env::var("SCYLLA_URI")
.unwrap_or_else(|_| "127.0.0.1:9042".to_string());
let session: Session = SessionBuilder::new().known_node(uri).build().await?;
// Schema metadata will be fetched below
session.refresh_metadata().await?;
let cluster_state = &session.get_cluster_state();
let keyspaces_iter = cluster_state.keyspaces_iter();
for (keyspace_name, keyspace_info) in keyspaces_iter {
println!("Keyspace {}:", keyspace_name);
println!("\tTables: {:#?}", keyspace_info.tables);
println!("\tViews: {:#?}", keyspace_info.views);
println!("\tUDTs: {:#?}", keyspace_info.user_defined_types);
}
Ok(())
}