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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.
//! Table source
use crate::{Expr, LogicalPlan};
use arrow::datatypes::SchemaRef;
use datafusion_common::{Constraints, Result};
use std::any::Any;
/// Indicates how a filter expression is handled by
/// [`TableProvider::scan`].
///
/// Filter expressions are boolean expressions used to reduce the number of
/// rows that are read from a table. Only rows that evaluate to `true` ("pass
/// the filter") are returned. Rows that evaluate to `false` or `NULL` are
/// omitted.
///
/// [`TableProvider::scan`]: https://docs.rs/datafusion/latest/datafusion/datasource/provider/trait.TableProvider.html#tymethod.scan
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum TableProviderFilterPushDown {
/// The filter cannot be used by the provider and will not be pushed down.
Unsupported,
/// The filter can be used, but the provider might still return some tuples
/// that do not pass the filter.
///
/// In this case, DataFusion applies an additional `Filter` operation
/// after the scan to ensure all rows are filtered correctly.
Inexact,
/// The provider **guarantees** that it will omit **only** tuples which
/// pass the filter.
///
/// In this case, DataFusion will not apply additional filtering.
Exact,
}
/// Indicates the type of this table for metadata/catalog purposes.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TableType {
/// An ordinary physical table.
Base,
/// A non-materialised table that itself uses a query internally to provide data.
View,
/// A transient table.
Temporary,
}
/// The TableSource trait is used during logical query planning and optimizations and
/// provides access to schema information and filter push-down capabilities. This trait
/// provides a subset of the functionality of the TableProvider trait in the core
/// datafusion crate. The TableProvider trait provides additional capabilities needed for
/// physical query execution (such as the ability to perform a scan). The reason for
/// having two separate traits is to avoid having the logical plan code be dependent
/// on the DataFusion execution engine. Other projects may want to use DataFusion's
/// logical plans and have their own execution engine.
pub trait TableSource: Sync + Send {
fn as_any(&self) -> &dyn Any;
/// Get a reference to the schema for this table
fn schema(&self) -> SchemaRef;
/// Get primary key indices, if one exists.
fn constraints(&self) -> Option<&Constraints> {
None
}
/// Get the type of this table for metadata/catalog purposes.
fn table_type(&self) -> TableType {
TableType::Base
}
/// Tests whether the table provider can make use of a filter expression
/// to optimise data retrieval.
#[deprecated(since = "20.0.0", note = "use supports_filters_pushdown instead")]
fn supports_filter_pushdown(
&self,
_filter: &Expr,
) -> Result<TableProviderFilterPushDown> {
Ok(TableProviderFilterPushDown::Unsupported)
}
/// Tests whether the table provider can make use of any or all filter expressions
/// to optimise data retrieval.
#[allow(deprecated)]
fn supports_filters_pushdown(
&self,
filters: &[&Expr],
) -> Result<Vec<TableProviderFilterPushDown>> {
filters
.iter()
.map(|f| self.supports_filter_pushdown(f))
.collect()
}
/// Get the Logical plan of this table provider, if available.
fn get_logical_plan(&self) -> Option<&LogicalPlan> {
None
}
/// Get the default value for a column, if available.
fn get_column_default(&self, _column: &str) -> Option<&Expr> {
None
}
}