datafusion 0.13.0

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//   http://www.apache.org/licenses/LICENSE-2.0
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//! A relation is a representation of a set of tuples. A database table is a
//! type of relation. During query execution, each operation on a relation (such as projection,
//! selection, aggregation) results in a new relation.

use std::sync::{Arc, Mutex};

use arrow::datatypes::Schema;
use arrow::record_batch::RecordBatch;

use crate::datasource::RecordBatchIterator;
use crate::error::Result;

/// trait for all relations (a relation is essentially just an iterator over batches
/// of data, with a known schema)
pub trait Relation {
    /// Get the next `RecordBatch`, or `None` if the iterator is exhausted
    fn next(&mut self) -> Result<Option<RecordBatch>>;

    /// get the schema for this relation
    fn schema(&self) -> &Arc<Schema>;
}

/// Implementation of a relation that represents a DataFusion data source
pub(super) struct DataSourceRelation {
    schema: Arc<Schema>,
    ds: Arc<Mutex<RecordBatchIterator>>,
}

impl DataSourceRelation {
    pub fn new(ds: Arc<Mutex<RecordBatchIterator>>) -> Self {
        let schema = ds.lock().unwrap().schema().clone();
        Self { ds, schema }
    }
}

impl Relation for DataSourceRelation {
    fn next(&mut self) -> Result<Option<RecordBatch>> {
        self.ds.lock().unwrap().next()
    }

    fn schema(&self) -> &Arc<Schema> {
        &self.schema
    }
}