Re: [PR] arrow_json: support decimal 128 and 256 types in json writer [arrow-rs]

["tustvold (via GitHub)" <gi...@apache.org>]

tustvold commented on code in PR #5197:
URL: https://github.com/apache/arrow-rs/pull/5197#discussion_r1422118258


##########
arrow-json/src/writer.rs:
##########
@@ -469,11 +469,67 @@ fn set_column_for_json_rows(
                 row.insert(col_name.to_string(), serde_json::Value::Object(obj));
             }
         }
+        DataType::Decimal128(_precision, _scale) | DataType::Decimal256(_precision, _scale) => {
+            to_json_float(rows, array, col_name, explicit_nulls)?;
+        }
         _ => {
             return Err(ArrowError::JsonError(format!(
-                "data type {:?} not supported in nested map for json writer",
+                "data type {:?} not supported for json writer",
                 array.data_type()
-            )))
+            )));
+        }
+    }
+    Ok(())
+}
+
+fn to_json_float(
+    rows: &mut [Option<JsonMap<String, Value>>],
+    array: &ArrayRef,
+    col_name: &str,
+    explicit_nulls: bool,
+) -> Result<(), ArrowError> {
+    let options = FormatOptions::default();
+    let formatter = ArrayFormatter::try_new(array.as_ref(), &options)?;

Review Comment:
   This will result in precision loss, decimals need to use the formatting logic in arrow-cast



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