DM-54471: Add backward compatible fix for pydantic 1

python/lsst/ci/models.py

@@ -364,7 +364,10 @@ def save(self, build_dir: str) -> None:
         # Write to build_dir
         try:
             with open(path, "w", encoding="utf-8") as f:
-                f.write(self.model_dump_json(indent=2))
+                if hasattr(self, "model_dump_json"):
+                    f.write(self.model_dump_json(indent=2))
+                else:  # fallback for pydantic v1
+                    f.write(self.json(indent=2))
         except OSError as os_err:
             print(f"Failed to write to {path}: {os_err}", file=sys.stderr)
 
@@ -384,6 +387,7 @@ def from_build_dir(cls, build_dir: str) -> AllProductPRCollections:
             The Pydantic model. If `pr_info.json` does not exist or fails
             to parse or validate, returns an empty model
             (`AllProductPRCollections(items=[])`).
+
         Warns
         -----
         Prints to `sys.stderr` on read, decode, or validation failures.
@@ -401,7 +405,11 @@ def from_build_dir(cls, build_dir: str) -> AllProductPRCollections:
             return cls(items=[])
 
         try:
-            return cls.model_validate_json(data)
+            if hasattr(cls, "model_validate_json"):
+                return cls.model_validate_json(data)
+            else:  # fallback for pydantic v1
+                return cls.parse_raw(data)
+
         except json.JSONDecodeError as decode_err:
             print(f"Invalid JSON in {path}: {decode_err}", file=sys.stderr)
         except pydantic.ValidationError as val_err: