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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.
//! An empty plan that is usefull for testing and generating plans without mapping them to actual data.
use std::any::Any;
use std::sync::Arc;
use arrow::datatypes::*;
use async_trait::async_trait;
use crate::datasource::TableProvider;
use crate::error::Result;
use crate::logical_plan::Expr;
use crate::physical_plan::project_schema;
use crate::physical_plan::{empty::EmptyExec, ExecutionPlan};
/// A table with a schema but no data.
pub struct EmptyTable {
schema: SchemaRef,
}
impl EmptyTable {
/// Initialize a new `EmptyTable` from a schema.
pub fn new(schema: SchemaRef) -> Self {
Self { schema }
}
}
#[async_trait]
impl TableProvider for EmptyTable {
fn as_any(&self) -> &dyn Any {
self
}
fn schema(&self) -> SchemaRef {
self.schema.clone()
}
async fn scan(
&self,
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.as_ref())?;
Ok(Arc::new(EmptyExec::new(false, projected_schema)))
}
}