1. user can choose to show nested type when write to csv 2. Add features to show struct type data as json format

arrow-cast/Cargo.toml

@@ -39,6 +39,7 @@ features = ["prettyprint"]
 [features]
 prettyprint = ["comfy-table"]
 force_validate = []
+struct_display_json =[]
 
 [dependencies]
 arrow-array = { workspace = true }
@@ -54,6 +55,7 @@ atoi = "2.0.0"
 comfy-table = { version = "7.0", optional = true, default-features = false }
 base64 = "0.22"
 ryu = "1.0.16"
+serde_json = "1.0"
 
 [dev-dependencies]
 criterion = { version = "0.5", default-features = false }

arrow-cast/src/display.rs

@@ -23,8 +23,10 @@
 //! record batch pretty printing.
 //!
 //! [`pretty`]: crate::pretty
+use std::collections::BTreeMap;
 use std::fmt::{Display, Formatter, Write};
 use std::ops::Range;
+use std::str::FromStr;
 
 use arrow_array::cast::*;
 use arrow_array::temporal_conversions::*;
@@ -938,7 +940,33 @@ impl<'a> DisplayIndexState<'a> for &'a StructArray {
             })
             .collect()
     }
+    #[cfg(feature = "struct_display_json")]
+    fn write(&self, s: &Self::State, idx: usize, f: &mut dyn Write) -> FormatResult {
+        let mut iter = s.iter();
 
+        let mut json = BTreeMap::<String, serde_json::Value>::new();
+        if let Some((name, display)) = iter.next() {
+            let mut display_str = String::new();
+            display.write(idx, &mut display_str)?;
+            json.insert(
+                name.to_string(),
+                serde_json::Value::from_str(&display_str)
+                    .unwrap_or(serde_json::Value::String(display_str)),
+            );
+        }
+        for (name, display) in iter {
+            let mut display_str = String::new();
+            display.write(idx, &mut display_str)?;
+            json.insert(
+                name.to_string(),
+                serde_json::Value::from_str(&display_str)
+                    .unwrap_or(serde_json::Value::String(display_str)),
+            );
+        }
+        let _ = f.write_str(&serde_json::to_string(&json).unwrap_or_default());
+        Ok(())
+    }
+    #[cfg(not(feature = "struct_display_json"))]
     fn write(&self, s: &Self::State, idx: usize, f: &mut dyn Write) -> FormatResult {
         let mut iter = s.iter();
         f.write_char('{')?;

arrow-csv/src/writer.rs

@@ -93,6 +93,9 @@ pub struct Writer<W: Write> {
     beginning: bool,
     /// The value to represent null entries, defaults to [`DEFAULT_NULL_VALUE`]
     null_value: Option<String>,
+
+    /// Show nested types to csv
+    show_nested: bool,
 }
 
 impl<W: Write> Writer<W> {
@@ -132,7 +135,7 @@ impl<W: Write> Writer<W> {
             .columns()
             .iter()
             .map(|a| {
-                if a.data_type().is_nested() {
+                if a.data_type().is_nested() && !self.show_nested {
                     Err(ArrowError::CsvError(format!(
                         "Nested type {} is not supported in CSV",
                         a.data_type()
@@ -211,6 +214,8 @@ pub struct WriterBuilder {
     time_format: Option<String>,
     /// Optional value to represent null
     null_value: Option<String>,
+    /// Show nested types to csv
+    show_nested: bool,
 }
 
 impl Default for WriterBuilder {
@@ -227,6 +232,7 @@ impl Default for WriterBuilder {
             timestamp_tz_format: None,
             time_format: None,
             null_value: None,
+            show_nested: false,
         }
     }
 }
@@ -389,6 +395,12 @@ impl WriterBuilder {
         self.null_value.as_deref().unwrap_or(DEFAULT_NULL_VALUE)
     }
 
+    /// Set whether to show nested fields
+    pub fn with_show_nested(mut self, show_nested: bool) -> Self {
+        self.show_nested = show_nested;
+        self
+    }
+
     /// Create a new `Writer`
     pub fn build<W: Write>(self, writer: W) -> Writer<W> {
         let mut builder = csv::WriterBuilder::new();
@@ -408,6 +420,7 @@ impl WriterBuilder {
             timestamp_format: self.timestamp_format,
             timestamp_tz_format: self.timestamp_tz_format,
             null_value: self.null_value,
+            show_nested: self.show_nested,
         }
     }
 }

arrow/Cargo.toml

@@ -66,6 +66,8 @@ csv = ["arrow-csv"]
 ipc = ["arrow-ipc"]
 json = ["arrow-json"]
 prettyprint = ["arrow-cast/prettyprint"]
+struct_display_json =["arrow-cast/struct_display_json"]
+
 # The test utils feature enables code used in benchmarks and tests but
 # not the core arrow code itself. Be aware that `rand` must be kept as
 # an optional dependency for supporting compile to wasm32-unknown-unknown