cisaacson commented on code in PR #9988:
URL: https://github.com/apache/arrow-datafusion/pull/9988#discussion_r1559349670
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datafusion/core/src/datasource/provider.rs:
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@@ -161,20 +161,83 @@ pub trait TableProvider: Sync + Send {
/// Specify if DataFusion should provide filter expressions to the
/// TableProvider to apply *during* the scan.
///
- /// The return value must have one element for each filter expression
passed
- /// in. The value of each element indicates if the TableProvider can apply
- /// that particular filter during the scan.
- ///
/// Some TableProviders can evaluate filters more efficiently than the
/// `Filter` operator in DataFusion, for example by using an index.
///
- /// By default, returns [`Unsupported`] for all filters, meaning no filters
- /// will be provided to [`Self::scan`]. If the TableProvider can implement
- /// filter pushdown, it should return either [`Exact`] or [`Inexact`].
+ /// # Parameters and Return Value
+ ///
+ /// The return `Vec` must have one element for each element of the
`filters`
+ /// argument. The value of each element indicates if the TableProvider can
+ /// apply the corresponding filter during the scan. The position in the
return
+ /// value corresponds to the expression in the `filters` parameter.
+ ///
+ /// If the length of the resulting `Vec` does not match the `filters` input
+ /// an error will be thrown.
+ ///
+ /// Each element in the resulting `Vec` is one of the following:
+ /// * [`Exact`] or [`Inexact`]: The TableProvider can apply the filter
+ /// during scan
+ /// * [`Unsupported`]: The TableProvider cannot apply the filter during
scan
+ ///
+ /// By default, this function returns [`Unsupported`] for all filters,
+ /// meaning no filters will be provided to [`Self::scan`].
///
/// [`Unsupported`]: TableProviderFilterPushDown::Unsupported
/// [`Exact`]: TableProviderFilterPushDown::Exact
/// [`Inexact`]: TableProviderFilterPushDown::Inexact
+ /// # Example
+ ///
+ /// ```rust
+ /// # use std::any::Any; /// #
+ /// # use std::sync::Arc;
+ /// # use arrow_schema::SchemaRef;
+ /// # use async_trait::async_trait;
+ /// # use datafusion::datasource::TableProvider;
+ /// # use datafusion::error::{Result, DataFusionError};
+ /// # use datafusion::execution::context::SessionState;
+ /// # use datafusion_expr::{Expr, TableProviderFilterPushDown, TableType};
+ /// # use datafusion_physical_plan::ExecutionPlan;
+ /// // Define a struct that implements the TableProvider trait
+ /// struct TestDataSource {}
+ ///
+ /// #[async_trait]
+ /// impl TableProvider for TestDataSource {
+ /// # fn as_any(&self) -> &dyn Any { todo!() }
+ /// # fn schema(&self) -> SchemaRef { todo!() }
+ /// # fn table_type(&self) -> TableType { todo!() }
+ /// # async fn scan(&self, s: &SessionState, p: Option<&Vec<usize>>, f:
&[Expr], l: Option<usize>) -> Result<Arc<dyn ExecutionPlan>> {
+ /// todo!()
+ /// # }
+ /// // Override the supports_filters_pushdown to evaluate which
expressions
+ /// // to accept as pushdown predicates.
+ /// fn supports_filters_pushdown(&self, filters: &[&Expr]) ->
Result<Vec<TableProviderFilterPushDown>> {
Review Comment:
@alamb Very nice, now I can see how to do this the right way, the code and
comments look very good. And understanding the `#` in doc comments helps too.
Looks great to me.
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