anonymous_scan.rs

use std::any::Any;
use std::fmt::{Debug, Formatter};

use polars_core::prelude::*;

use crate::dsl::Expr;

pub struct AnonymousScanArgs {
    pub n_rows: Option<usize>,
    pub with_columns: Option<Arc<[PlSmallStr]>>,
    pub schema: SchemaRef,
    pub output_schema: Option<SchemaRef>,
    pub predicate: Option<Expr>,
}

pub trait AnonymousScan: Send + Sync {
    fn as_any(&self) -> &dyn Any;
    /// Creates a DataFrame from the supplied function & scan options.
    fn scan(&self, scan_opts: AnonymousScanArgs) -> PolarsResult<DataFrame>;

    /// Produce the next batch Polars can consume. Implement this method to get proper
    /// streaming support.
    fn next_batch(&self, scan_opts: AnonymousScanArgs) -> PolarsResult<Option<DataFrame>> {
        self.scan(scan_opts).map(Some)
    }

    /// function to supply the schema.
    /// Allows for an optional infer schema argument for data sources with dynamic schemas
    fn schema(&self, _infer_schema_length: Option<usize>) -> PolarsResult<SchemaRef> {
        polars_bail!(ComputeError: "must supply either a schema or a schema function");
    }
    /// Specify if the scan provider should allow predicate pushdowns.
    ///
    /// Defaults to `false`
    fn allows_predicate_pushdown(&self) -> bool {
        false
    }
    /// Specify if the scan provider should allow projection pushdowns.
    ///
    /// Defaults to `false`
    fn allows_projection_pushdown(&self) -> bool {
        false
    }
    /// Specify if the scan provider should allow slice pushdowns.
    ///
    /// Defaults to `false`
    fn allows_slice_pushdown(&self) -> bool {
        false
    }
}

impl Debug for dyn AnonymousScan {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        write!(f, "anonymous_scan")
    }
}