andygrove commented on code in PR #9988:
URL: https://github.com/apache/arrow-datafusion/pull/9988#discussion_r1558416804
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datafusion/core/src/datasource/provider.rs:
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@@ -161,20 +161,73 @@ pub trait TableProvider: Sync + Send {
/// Specify if DataFusion should provide filter expressions to the
/// TableProvider to apply *during* the scan.
///
+ /// Some TableProviders can evaluate filters more efficiently than the
+ /// `Filter` operator in DataFusion, for example by using an index.
+ ///
/// 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.
+ /// that particular filter during the scan. The position in the return
value
+ /// Vec corresponds to the expression in the `filters` input.
+ ///
+ /// Here is an example of how this can be done:
+ ///
+ /// ```rust
+ /// use datafusion::error::{Result, DataFusionError};
+ /// use datafusion_expr::{Expr, TableProviderFilterPushDown};
+ ///
+ /// // Override the supports_filters_pushdown to evaluate which
expressions
+ /// // to accept as pushdown predicates.
+ /// fn supports_filters_pushdown(&self, filters: &[&Expr]) ->
Result<Vec<TableProviderFilterPushDown>> {
///
- /// Some TableProviders can evaluate filters more efficiently than the
- /// `Filter` operator in DataFusion, for example by using an index.
+ /// let mut result_vec: Vec<TableProviderFilterPushDown> =
Vec::with_capacity(&filters.len());
///
- /// By default, returns [`Unsupported`] for all filters, meaning no filters
+ /// // Process each filter
+ /// for i in 0..filters.len() {
+ /// let expr = *filters[i];
+ ///
+ /// let table_provider_filter_pushdown = match expr {
+ /// // This example only supports a between expr with a single
column name.
+ /// Expr::Between(between_expr) => {
+ /// between_expr.expr.try_into_col()
+ /// .map(|column| {
+ /// if column.name = "c1".to_string() {
Review Comment:
This needs to be a comparison and not an assignment
```suggestion
/// if column.name == "c1".to_string() {
```
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