implement variant_get_json

Author: friendlymatthew

src/variant_get.rs

@@ -296,6 +296,25 @@ impl_variant_get_typed!(
     |value: Variant<'_, '_>| -> Result<Option<bool>> { Ok(value.as_boolean()) },
 );
 
+impl_variant_get_typed!(
+    /// Extracts a value from a Variant by path and returns it as a JSON string.
+    ///
+    /// `variant_get_json(variant, path)` returns the value at `path` as a JSON string.
+    /// - All values are JSON-serialized (strings include quotes, unlike `variant_get_str`)
+    /// - Returns NULL if the path does not exist
+    VariantGetJsonUdf,
+    "variant_get_json",
+    DataType::Utf8View,
+    ScalarValue::Utf8View,
+    |values: Vec<Option<String>>| -> ArrayRef {
+        let out: StringViewArray = values.into_iter().collect();
+        Arc::new(out)
+    },
+    |value: Variant<'_, '_>| -> Result<Option<String>> {
+        Ok(Some(value.to_json_string()?))
+    },
+);
+
 #[derive(Debug, Hash, PartialEq, Eq)]
 pub struct VariantGetUdf {
     signature: Signature,

tests/sqllogictests.rs

@@ -2,9 +2,9 @@ use datafusion::{logical_expr::ScalarUDF, prelude::*};
 use datafusion_sqllogictest::{DataFusion, TestContext};
 use datafusion_variant::{
     CastToVariantUdf, IsVariantNullUdf, JsonToVariantUdf, VariantGetBoolUdf, VariantGetFieldUdf,
-    VariantGetFloatUdf, VariantGetIntUdf, VariantGetStrUdf, VariantGetUdf, VariantListConstruct,
-    VariantListDelete, VariantListInsert, VariantObjectConstruct, VariantObjectDelete,
-    VariantObjectInsert, VariantObjectKeys, VariantPretty, VariantToJsonUdf,
+    VariantGetFloatUdf, VariantGetIntUdf, VariantGetJsonUdf, VariantGetStrUdf, VariantGetUdf,
+    VariantListConstruct, VariantListDelete, VariantListInsert, VariantObjectConstruct,
+    VariantObjectDelete, VariantObjectInsert, VariantObjectKeys, VariantPretty, VariantToJsonUdf,
 };
 use indicatif::ProgressBar;
 use sqllogictest::strict_column_validator;
@@ -54,6 +54,7 @@ async fn run_sqllogictests() -> Result<(), Box<dyn std::error::Error>> {
         ctx.register_udf(ScalarUDF::new_from_impl(VariantGetFloatUdf::default()));
         ctx.register_udf(ScalarUDF::new_from_impl(VariantGetIntUdf::default()));
         ctx.register_udf(ScalarUDF::new_from_impl(VariantGetBoolUdf::default()));
+        ctx.register_udf(ScalarUDF::new_from_impl(VariantGetJsonUdf::default()));
         ctx.register_udf(ScalarUDF::new_from_impl(VariantGetFieldUdf::default()));
         ctx.register_udf(ScalarUDF::new_from_impl(VariantPretty::default()));
         ctx.register_udf(ScalarUDF::new_from_impl(VariantObjectConstruct::default()));

tests/test_files/variant_get_json.slt

@@ -0,0 +1,112 @@
+statement ok
+CREATE TABLE json_data (id INT, json_str TEXT) AS VALUES
+  (1, '{"name": "Alice", "age": 30}'),
+  (2, '{"name": "Bob", "age": 25}'),
+  (3, '{"items": [1, 2, 3], "count": 3}'),
+  (4, 'null'),
+  (5, '"simple string"'),
+  (6, '123'),
+  (7, 'true'),
+  (8, '{"pi": 3.14, "active": true}');
+
+# string values are returned with json quotes (unlike variant_get_str)
+query T
+select variant_get_json(json_to_variant(json_str), 'name') from json_data;
+----
+"Alice"
+"Bob"
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+
+# integer values are json-serialized
+query T
+select variant_get_json(json_to_variant(json_str), 'age') from json_data;
+----
+30
+25
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+
+# float values are json-serialized
+query T
+select variant_get_json(json_to_variant(json_str), 'pi') from json_data;
+----
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+3.14
+
+# boolean values are json-serialized
+query T
+select variant_get_json(json_to_variant(json_str), 'active') from json_data;
+----
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+true
+
+# array values are json-serialized
+query T
+select variant_get_json(json_to_variant(json_str), 'items') from json_data;
+----
+NULL
+NULL
+[1,2,3]
+NULL
+NULL
+NULL
+NULL
+NULL
+
+# missing paths return null
+query T
+select variant_get_json(json_to_variant(json_str), 'nonexistent') from json_data;
+----
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+
+# scalar variant with nested object
+query T
+select variant_get_json(json_to_variant('{"obj": {"a": 1}}'), 'obj');
+----
+{"a":1}
+
+# scalar variant with null value
+query T
+select variant_get_json(json_to_variant('{"key": null}'), 'key');
+----
+null
+
+# nested path
+query T
+select variant_get_json(json_to_variant('{"obj": {"a": "hello"}}'), 'obj.a');
+----
+"hello"
+
+# nested numeric path
+query T
+select variant_get_json(json_to_variant('{"obj": {"a": 42}}'), 'obj.a');
+----
+42