context.rs

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//
//   http://www.apache.org/licenses/LICENSE-2.0
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//! Context (remote or local)

use datafusion::dataframe::DataFrame;
use datafusion::error::{DataFusionError, Result};
use datafusion::execution::context::{ExecutionConfig, ExecutionContext};
use std::sync::Arc;

/// The CLI supports using a local DataFusion context or a distributed BallistaContext
pub enum Context {
    /// In-process execution with DataFusion
    Local(ExecutionContext),
    /// Distributed execution with Ballista (if available)
    Remote(BallistaContext),
}

impl Context {
    /// create a new remote context with given host and port
    pub fn new_remote(host: &str, port: u16) -> Result<Context> {
        Ok(Context::Remote(BallistaContext::try_new(host, port)?))
    }

    /// create a local context using the given config
    pub fn new_local(config: &ExecutionConfig) -> Context {
        Context::Local(ExecutionContext::with_config(config.clone()))
    }

    /// execute an SQL statement against the context
    pub async fn sql(&mut self, sql: &str) -> Result<Arc<DataFrame>> {
        match self {
            Context::Local(datafusion) => datafusion.sql(sql).await,
            Context::Remote(ballista) => ballista.sql(sql).await,
        }
    }
}

// implement wrappers around the BallistaContext to support running without ballista

#[cfg(feature = "ballista")]
pub struct BallistaContext(ballista::context::BallistaContext);
#[cfg(feature = "ballista")]
impl BallistaContext {
    pub fn try_new(host: &str, port: u16) -> Result<Self> {
        use ballista::context::BallistaContext;
        use ballista::prelude::BallistaConfig;
        let config: BallistaConfig = BallistaConfig::new()
            .map_err(|e| DataFusionError::Execution(format!("{:?}", e)))?;
        Ok(Self(BallistaContext::remote(host, port, &config)))
    }
    pub async fn sql(&mut self, sql: &str) -> Result<Arc<DataFrame>> {
        self.0.sql(sql).await
    }
}

#[cfg(not(feature = "ballista"))]
pub struct BallistaContext();
#[cfg(not(feature = "ballista"))]
impl BallistaContext {
    pub fn try_new(_host: &str, _port: u16) -> Result<Self> {
        Err(DataFusionError::NotImplemented(
            "Remote execution not supported. Compile with feature 'ballista' to enable"
                .to_string(),
        ))
    }
    pub async fn sql(&mut self, _sql: &str) -> Result<Arc<DataFrame>> {
        unreachable!()
    }
}