[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #2284: Remove dependency from `LogicalPlan::TableScan` to `ExecutionPlan`

[GitBox <gi...@apache.org>]

alamb commented on code in PR #2284:
URL: https://github.com/apache/arrow-datafusion/pull/2284#discussion_r854563327


##########
datafusion/core/src/logical_plan/plan.rs:
##########
@@ -125,13 +127,71 @@ pub struct Window {
     pub schema: DFSchemaRef,
 }
 
+/// DataFusion default table source, wrapping TableProvider
+pub struct DefaultTableSource {
+    /// table provider
+    pub table_provider: Arc<dyn TableProvider>,
+}
+
+impl DefaultTableSource {
+    /// Create a new DefaultTableSource to wrap a TableProvider
+    pub fn new(table_provider: Arc<dyn TableProvider>) -> Self {
+        Self { table_provider }
+    }
+}
+
+impl TableSource for DefaultTableSource {
+    /// Returns the table source as [`Any`](std::any::Any) so that it can be
+    /// downcast to a specific implementation.
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    /// Get a reference to the schema for this table
+    fn schema(&self) -> SchemaRef {
+        self.table_provider.schema()
+    }
+
+    /// Tests whether the table provider can make use of a filter expression
+    /// to optimise data retrieval.
+    fn supports_filter_pushdown(
+        &self,
+        filter: &Expr,
+    ) -> datafusion_common::Result<TableProviderFilterPushDown> {
+        self.table_provider.supports_filter_pushdown(filter)
+    }
+}
+
+/// Wrap TableProvider in TableSource
+pub fn provider_as_source(
+    table_provider: Arc<dyn TableProvider>,
+) -> Arc<dyn TableSource> {
+    Arc::new(DefaultTableSource::new(table_provider))
+}
+
+/// Extract TableProvider from TableSource
+pub fn source_as_provider(

Review Comment:
   Maybe it is worth a comment on `TableSource` that it is not intended, initially, to be extended outside of DataFusion.



##########
datafusion/expr/src/table_source.rs:
##########
@@ -0,0 +1,72 @@
+// 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.
+
+use crate::Expr;
+use arrow::datatypes::SchemaRef;
+use std::any::Any;
+
+///! Table source
+
+/// Indicates whether and how a filter expression can be handled by a
+/// TableProvider for table scans.
+#[derive(Debug, Clone, PartialEq)]
+pub enum TableProviderFilterPushDown {
+    /// The expression cannot be used by the provider.
+    Unsupported,
+    /// The expression can be used to help minimise the data retrieved,
+    /// but the provider cannot guarantee that all returned tuples
+    /// satisfy the filter. The Filter plan node containing this expression
+    /// will be preserved.
+    Inexact,
+    /// The provider guarantees that all returned data satisfies this
+    /// filter expression. The Filter plan node containing this expression
+    /// will be removed.
+    Exact,
+}
+
+/// Indicates the type of this table for metadata/catalog purposes.
+#[derive(Debug, Clone, Copy, PartialEq)]
+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,
+}
+
+/// TableSource

Review Comment:
   It is probably worth some comments here about the rationale for this structure existing -- namely so LogicalPlan doesn't directly rely on physical plans



##########
datafusion/core/src/logical_plan/plan.rs:
##########
@@ -125,13 +127,71 @@ pub struct Window {
     pub schema: DFSchemaRef,
 }
 
+/// DataFusion default table source, wrapping TableProvider

Review Comment:
   ```suggestion
   /// DataFusion default table source, wrapping TableProvider
   ///
   /// This structure adapts a `TableProvider` (physical plan trait) to the `TableSource` 
   /// (logical plan trait)
   ```



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