Initial code, spec and test, pushing for review

Author: anupkalburgi

dbldatagen/spec/compat.py

@@ -7,12 +7,25 @@
 
 except ImportError:
     # This will be executed on environments with only Pydantic V1.x
-    from pydantic import BaseModel, Field, validator, constr
+    from pydantic import BaseModel, Field, validator, constr, root_validator, field_validator
 
 # In your application code, do this:
 # from .compat import BaseModel
 # NOT this:
 # from pydantic import BaseModel
 
 # FastAPI Notes
-# https://github.com/fastapi/fastapi/blob/master/fastapi/_compat.py
+# https://github.com/fastapi/fastapi/blob/master/fastapi/_compat.py
+
+
+"""
+## Why This Approach
+No Installation Required: It directly addresses your core requirement.
+You don't need to %pip install anything, which avoids conflicts with the pre-installed libraries on Databricks.
+Single Codebase: You maintain one set of code that is guaranteed to work with the Pydantic V1 API, which is available in both runtimes.
+
+Environment Agnostic: Your application code in models.py has no idea which version of Pydantic is actually installed. The compat.py module handles that complexity completely.
+
+Future-Ready: When you eventually decide to migrate fully to the Pydantic V2 API (to take advantage of its speed and features),
+you only need to change your application code and your compat.py import statements, making the transition much clearer.
+"""