Migrate data models to pydantic (#267)

This PR introduces `pydantic` to handle all validation, parsing and serialising.

Author: jm-rivera

datacommons_client/client.py

@@ -3,8 +3,8 @@
 from datacommons_client.endpoints.base import API
 from datacommons_client.endpoints.node import NodeEndpoint
 from datacommons_client.endpoints.observation import ObservationEndpoint
-from datacommons_client.endpoints.payloads import ObservationDate
 from datacommons_client.endpoints.resolve import ResolveEndpoint
+from datacommons_client.models.observation import ObservationDate
 from datacommons_client.utils.dataframes import add_entity_names_to_observations_dataframe
 from datacommons_client.utils.decorators import requires_pandas
 from datacommons_client.utils.error_handling import NoDataForPropertyError
@@ -184,7 +184,7 @@ def observations_dataframe(
           filter_facet_ids=facets)
 
     # Convert the observations to a DataFrame
-    df = pd.DataFrame(observations.to_observation_records())
+    df = pd.DataFrame(observations.to_observation_records().model_dump())
 
     # Add entity names to the DataFrame
     df = add_entity_names_to_observations_dataframe(

datacommons_client/endpoints/node.py

@@ -7,7 +7,7 @@
 from datacommons_client.endpoints.base import API
 from datacommons_client.endpoints.base import Endpoint
 from datacommons_client.endpoints.payloads import NodeRequestPayload
-from datacommons_client.endpoints.payloads import normalize_properties_to_string
+from datacommons_client.endpoints.payloads import normalize_list_to_string
 from datacommons_client.endpoints.response import NodeResponse
 from datacommons_client.models.node import Name
 from datacommons_client.models.node import Node
@@ -115,10 +115,10 @@ def fetch(
 
     # Create the payload
     payload = NodeRequestPayload(node_dcids=node_dcids,
-                                 expression=expression).to_dict
+                                 expression=expression).to_dict()
 
     # Make the request and return the response.
-    return NodeResponse.from_json(
+    return NodeResponse.model_validate(
         self.post(payload, all_pages=all_pages, next_token=next_token))
 
   def fetch_property_labels(
@@ -199,7 +199,7 @@ def fetch_property_values(
         """
 
     # Normalize the input to a string (if it's a list), otherwise use the string as is.
-    properties = normalize_properties_to_string(properties)
+    properties = normalize_list_to_string(properties)
 
     # Construct the expression based on the direction and constraints.
     direction = "->" if out else "<-"

datacommons_client/endpoints/observation.py

@@ -2,10 +2,10 @@
 
 from datacommons_client.endpoints.base import API
 from datacommons_client.endpoints.base import Endpoint
-from datacommons_client.endpoints.payloads import ObservationDate
 from datacommons_client.endpoints.payloads import ObservationRequestPayload
-from datacommons_client.endpoints.payloads import ObservationSelect
 from datacommons_client.endpoints.response import ObservationResponse
+from datacommons_client.models.observation import ObservationDate
+from datacommons_client.models.observation import ObservationSelect
 from datacommons_client.utils.data_processing import group_variables_by_entity
 
 
@@ -58,10 +58,12 @@ def fetch(
         entity_expression=entity_expression,
         filter_facet_domains=filter_facet_domains,
         filter_facet_ids=filter_facet_ids,
-    ).to_dict
+    ).to_dict()
+
+    response = self.post(payload)
 
     # Send the request
-    return ObservationResponse.from_json(self.post(payload))
+    return ObservationResponse.model_validate(response)
 
   def fetch_observations_by_entity_type(
       self,