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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.
//! [`EmptyTable`] useful for testing.
use std::any::Any;
use std::sync::Arc;
use arrow::datatypes::*;
use async_trait::async_trait;
use crate::datasource::{TableProvider, TableType};
use crate::error::Result;
use crate::execution::context::SessionState;
use crate::logical_expr::Expr;
use crate::physical_plan::project_schema;
use crate::physical_plan::{empty::EmptyExec, ExecutionPlan};
/// An empty plan that is useful for testing and generating plans
/// without mapping them to actual data.
pub struct EmptyTable {
schema: SchemaRef,
partitions: usize,
}
impl EmptyTable {
/// Initialize a new `EmptyTable` from a schema.
pub fn new(schema: SchemaRef) -> Self {
Self {
schema,
partitions: 1,
}
}
/// Creates a new EmptyTable with specified partition number.
pub fn with_partitions(mut self, partitions: usize) -> Self {
self.partitions = partitions;
self
}
}
#[async_trait]
impl TableProvider for EmptyTable {
fn as_any(&self) -> &dyn Any {
self
}
fn schema(&self) -> SchemaRef {
self.schema.clone()
}
fn table_type(&self) -> TableType {
TableType::Base
}
async fn scan(
&self,
_state: &SessionState,
projection: Option<&Vec<usize>>,
_filters: &[Expr],
_limit: Option<usize>,
) -> Result<Arc<dyn ExecutionPlan>> {
// even though there is no data, projections apply
let projected_schema = project_schema(&self.schema, projection)?;
Ok(Arc::new(
EmptyExec::new(false, projected_schema).with_partitions(self.partitions),
))
}
}