fix: resolve arrow-pg panic when encoding dictionary arrays (#142)

* added dict bug fix

* formatted

Author: savs02

arrow-pg/src/encoder.rs

@@ -513,38 +513,31 @@ pub fn encode_value<T: Encoder>(
             if arr.is_null(idx) {
                 return encoder.encode_field_with_type_and_format(&None::<i8>, type_, format);
             }
-            // Get the dictionary values, ignoring keys
-            // We'll use Int32Type as a common key type, but we're only interested in values
-            macro_rules! get_dict_values {
+            // Get the dictionary values and the mapped row index
+            macro_rules! get_dict_values_and_index {
                 ($key_type:ty) => {
                     arr.as_any()
                         .downcast_ref::<DictionaryArray<$key_type>>()
-                        .map(|dict| dict.values())
+                        .map(|dict| (dict.values(), dict.keys().value(idx) as usize))
                 };
             }
 
             // Try to extract values using different key types
-            let values = get_dict_values!(Int8Type)
-                .or_else(|| get_dict_values!(Int16Type))
-                .or_else(|| get_dict_values!(Int32Type))
-                .or_else(|| get_dict_values!(Int64Type))
-                .or_else(|| get_dict_values!(UInt8Type))
-                .or_else(|| get_dict_values!(UInt16Type))
-                .or_else(|| get_dict_values!(UInt32Type))
-                .or_else(|| get_dict_values!(UInt64Type))
+            let (values, idx) = get_dict_values_and_index!(Int8Type)
+                .or_else(|| get_dict_values_and_index!(Int16Type))
+                .or_else(|| get_dict_values_and_index!(Int32Type))
+                .or_else(|| get_dict_values_and_index!(Int64Type))
+                .or_else(|| get_dict_values_and_index!(UInt8Type))
+                .or_else(|| get_dict_values_and_index!(UInt16Type))
+                .or_else(|| get_dict_values_and_index!(UInt32Type))
+                .or_else(|| get_dict_values_and_index!(UInt64Type))
                 .ok_or_else(|| {
                     ToSqlError::from(format!(
                         "Unsupported dictionary key type for value type {value_type}"
                     ))
                 })?;
 
-            // If the dictionary has only one value, treat it as a primitive
-            if values.len() == 1 {
-                encode_value(encoder, values, 0, type_, format)?
-            } else {
-                // Otherwise, use value directly indexed by values array
-                encode_value(encoder, values, idx, type_, format)?
-            }
+            encode_value(encoder, values, idx, type_, format)?
         }
         _ => {
             return Err(PgWireError::ApiError(ToSqlError::from(format!(
@@ -557,3 +550,48 @@ pub fn encode_value<T: Encoder>(
 
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn encodes_dictionary_array() {
+        #[derive(Default)]
+        struct MockEncoder {
+            encoded_value: String,
+        }
+
+        impl Encoder for MockEncoder {
+            fn encode_field_with_type_and_format<T>(
+                &mut self,
+                value: &T,
+                data_type: &Type,
+                _format: FieldFormat,
+            ) -> PgWireResult<()>
+            where
+                T: ToSql + ToSqlText + Sized,
+            {
+                let mut bytes = BytesMut::new();
+                let _sql_text = value.to_sql_text(data_type, &mut bytes);
+                let string = String::from_utf8((&bytes).to_vec());
+                self.encoded_value = string.unwrap();
+                Ok(())
+            }
+        }
+
+        let val = "~!@&$[]()@@!!";
+        let value = StringArray::from_iter_values([val]);
+        let keys = Int8Array::from_iter_values([0, 0, 0, 0]);
+        let dict_arr: Arc<dyn Array> =
+            Arc::new(DictionaryArray::<Int8Type>::try_new(keys, Arc::new(value)).unwrap());
+
+        let mut encoder = MockEncoder::default();
+
+        let result = encode_value(&mut encoder, &dict_arr, 2, &Type::TEXT, FieldFormat::Text);
+
+        assert!(result.is_ok());
+
+        assert!(encoder.encoded_value == val);
+    }
+}