Fix: CORE Filter serialization

The Filter class' str method would not be called,
and the pydantic serialization logic could not deduce it.

Add an explicit field serializer to make it str.

Author: Epse

src/obelisk/asynchronous/core.py

@@ -24,6 +24,7 @@
     model_validator,
     SerializerFunctionWrapHandler,
     WrapSerializer,
+    field_serializer,
 )
 from typing import (
     Annotated,
@@ -157,7 +158,7 @@ class QueryParams(BaseModel):
     """List of Field Names, with their potential prefixes and suffixes, to select ordering. None user server defaults."""
     dataType: DataType | None = None
     """Data type expected to be returned, is mandatory if the `value` field is requested in the `fields` parameter"""
-    filter_: Annotated[str | Filter | None, Field(serialization_alias="filter")] = None
+    filter_: Annotated[str | Filter | None, Field(serialization_alias="filter",)] = None
     """
     Obelisk CORE handles filtering in [RSQL format](https://obelisk.pages.ilabt.imec.be/obelisk-core/query.html#rsql-format),
     to make it easier to also programatically write these filters, we provide the `obelisk.types.core.Filter` option as well.
@@ -181,6 +182,13 @@ def to_dict(self) -> dict[str, Any]:
             exclude_none=True, by_alias=True, mode="json", exclude={"dataset"}
         )
 
+    @field_serializer('filter_', mode='plain')
+    def serialize_filter(self, value: Filter | str | None) -> str | None:
+        if value is None or isinstance(value, str):
+            return value
+
+        return str(value)
+
 
 class ChunkedParams(BaseModel):
     """

src/tests/asynchronous/core_test.py

@@ -1,4 +1,5 @@
 from obelisk.asynchronous.core import QueryParams
+from obelisk.types.core import Filter, Comparison
 
 
 def test_query_param_serialize():
@@ -24,3 +25,14 @@ def test_comma_separate_string():
     assert data["groupBy"] == "dataset,timestamp"
     assert data["orderBy"] == "timestamp,value"
 
+
+
+def test_filter_serialize():
+    filter_ = Filter().add_and(Comparison.equal("metric", "smartphone.acceleration::number[]"), Comparison.greater_equal("timestamp", 123456))
+    q = QueryParams(
+        dataset="83989232",
+        filter_=filter_,
+        dataType="number[]",
+    )
+    dump = q.to_dict()
+    assert "filter" in dump