Allow SessionContext::read_csv, etc to read multiple files (#4908)

* Added a traitDataFilePaths to convert strings and vector of strings to a vector of URLs.

* Added docs and tests. Updated DataFilePaths to accept any vector containing AsRef<str> trait.

* Added docs to read_ methods and extended the SessionContext doc.

* Ran Cargo fmt

* removed CallReadTrait methods

* Update read_csv example

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

* removed addition to SessionContext example

---------

Co-authored-by: Lakkam Sai Krishna Reddy <lakkam.saikrishnareddy@gmail.com>
Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: 3 people

datafusion/core/src/execution/context.rs

@@ -106,6 +106,43 @@ use super::options::{
     AvroReadOptions, CsvReadOptions, NdJsonReadOptions, ParquetReadOptions, ReadOptions,
 };
 
+/// DataFilePaths adds a method to convert strings and vector of strings to vector of [`ListingTableUrl`] URLs.
+/// This allows methods such [`SessionContext::read_csv`] and `[`SessionContext::read_avro`]
+/// to take either a single file or multiple files.
+pub trait DataFilePaths {
+    /// Parse to a vector of [`ListingTableUrl`] URLs.
+    fn to_urls(self) -> Result<Vec<ListingTableUrl>>;
+}
+
+impl DataFilePaths for &str {
+    fn to_urls(self) -> Result<Vec<ListingTableUrl>> {
+        Ok(vec![ListingTableUrl::parse(self)?])
+    }
+}
+
+impl DataFilePaths for String {
+    fn to_urls(self) -> Result<Vec<ListingTableUrl>> {
+        Ok(vec![ListingTableUrl::parse(self)?])
+    }
+}
+
+impl DataFilePaths for &String {
+    fn to_urls(self) -> Result<Vec<ListingTableUrl>> {
+        Ok(vec![ListingTableUrl::parse(self)?])
+    }
+}
+
+impl<P> DataFilePaths for Vec<P>
+where
+    P: AsRef<str>,
+{
+    fn to_urls(self) -> Result<Vec<ListingTableUrl>> {
+        self.iter()
+            .map(ListingTableUrl::parse)
+            .collect::<Result<Vec<ListingTableUrl>>>()
+    }
+}
+
 /// SessionContext is the main interface for executing queries with DataFusion. It stands for
 /// the connection between user and DataFusion/Ballista cluster.
 /// The context provides the following functionality
@@ -627,22 +664,18 @@ impl SessionContext {
     ///
     /// For more control such as reading multiple files, you can use
     /// [`read_table`](Self::read_table) with a [`ListingTable`].
-    async fn _read_type<'a>(
+    async fn _read_type<'a, P: DataFilePaths>(
         &self,
-        table_path: impl AsRef<str>,
+        table_paths: P,
         options: impl ReadOptions<'a>,
     ) -> Result<DataFrame> {
-        let table_path = ListingTableUrl::parse(table_path)?;
+        let table_paths = table_paths.to_urls()?;
         let session_config = self.copied_config();
         let listing_options = options.to_listing_options(&session_config);
-        let resolved_schema = match options
-            .get_resolved_schema(&session_config, self.state(), table_path.clone())
-            .await
-        {
-            Ok(resolved_schema) => resolved_schema,
-            Err(e) => return Err(e),
-        };
-        let config = ListingTableConfig::new(table_path)
+        let resolved_schema = options
+            .get_resolved_schema(&session_config, self.state(), table_paths[0].clone())
+            .await?;
+        let config = ListingTableConfig::new_with_multi_paths(table_paths)
             .with_listing_options(listing_options)
             .with_schema(resolved_schema);
         let provider = ListingTable::try_new(config)?;
@@ -653,24 +686,28 @@ impl SessionContext {
     ///
     /// For more control such as reading multiple files, you can use
     /// [`read_table`](Self::read_table) with a [`ListingTable`].
-    pub async fn read_avro(
+    ///
+    /// For an example, see [`read_csv`](Self::read_csv)
+    pub async fn read_avro<P: DataFilePaths>(
         &self,
-        table_path: impl AsRef<str>,
+        table_paths: P,
         options: AvroReadOptions<'_>,
     ) -> Result<DataFrame> {
-        self._read_type(table_path, options).await
+        self._read_type(table_paths, options).await
     }
 
     /// Creates a [`DataFrame`] for reading an JSON data source.
     ///
     /// For more control such as reading multiple files, you can use
     /// [`read_table`](Self::read_table) with a [`ListingTable`].
-    pub async fn read_json(
+    ///
+    /// For an example, see [`read_csv`](Self::read_csv)
+    pub async fn read_json<P: DataFilePaths>(
         &self,
-        table_path: impl AsRef<str>,
+        table_paths: P,
         options: NdJsonReadOptions<'_>,
     ) -> Result<DataFrame> {
-        self._read_type(table_path, options).await
+        self._read_type(table_paths, options).await
     }
 
     /// Creates an empty DataFrame.
@@ -685,24 +722,42 @@ impl SessionContext {
     ///
     /// For more control such as reading multiple files, you can use
     /// [`read_table`](Self::read_table) with a [`ListingTable`].
-    pub async fn read_csv(
+    ///
+    /// Example usage is given below:
+    ///
+    /// ```
+    /// use datafusion::prelude::*;
+    /// # use datafusion::error::Result;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<()> {
+    /// let ctx = SessionContext::new();
+    /// // You can read a single file using `read_csv`
+    /// let df = ctx.read_csv("tests/data/example.csv", CsvReadOptions::new()).await?;
+    /// // you can also read multiple files:
+    /// let df = ctx.read_csv(vec!["tests/data/example.csv", "tests/data/example.csv"], CsvReadOptions::new()).await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn read_csv<P: DataFilePaths>(
         &self,
-        table_path: impl AsRef<str>,
+        table_paths: P,
         options: CsvReadOptions<'_>,
     ) -> Result<DataFrame> {
-        self._read_type(table_path, options).await
+        self._read_type(table_paths, options).await
     }
 
     /// Creates a [`DataFrame`] for reading a Parquet data source.
     ///
     /// For more control such as reading multiple files, you can use
     /// [`read_table`](Self::read_table) with a [`ListingTable`].
-    pub async fn read_parquet(
+    ///
+    /// For an example, see [`read_csv`](Self::read_csv)
+    pub async fn read_parquet<P: DataFilePaths>(
         &self,
-        table_path: impl AsRef<str>,
+        table_paths: P,
         options: ParquetReadOptions<'_>,
     ) -> Result<DataFrame> {
-        self._read_type(table_path, options).await
+        self._read_type(table_paths, options).await
     }
 
     /// Creates a [`DataFrame`] for a [`TableProvider`] such as a