Add support for specifying column type.

Instead of having to set the whole column, we can just override the type
of the field itself. This works much nicer with the rest of sqlmodel.

Author: tasn

sqlmodel/main.py

@@ -1,4 +1,5 @@
 import ipaddress
+from sqlalchemy.sql.type_api import TypeEngine
 import uuid
 import weakref
 from datetime import date, datetime, time, timedelta
@@ -72,6 +73,7 @@ def __init__(self, default: Any = Undefined, **kwargs: Any) -> None:
         foreign_key = kwargs.pop("foreign_key", Undefined)
         index = kwargs.pop("index", Undefined)
         sa_column = kwargs.pop("sa_column", Undefined)
+        sa_column_type = kwargs.pop("sa_column_type", Undefined)
         sa_column_args = kwargs.pop("sa_column_args", Undefined)
         sa_column_kwargs = kwargs.pop("sa_column_kwargs", Undefined)
         if sa_column is not Undefined:
@@ -91,6 +93,7 @@ def __init__(self, default: Any = Undefined, **kwargs: Any) -> None:
         self.foreign_key = foreign_key
         self.index = index
         self.sa_column = sa_column
+        self.sa_column_type = sa_column_type
         self.sa_column_args = sa_column_args
         self.sa_column_kwargs = sa_column_kwargs
 
@@ -153,6 +156,7 @@ def Field(
     nullable: Union[bool, UndefinedType] = Undefined,
     index: Union[bool, UndefinedType] = Undefined,
     sa_column: Union[Column, UndefinedType] = Undefined,
+    sa_column_type: Union[TypeEngine, UndefinedType] = Undefined,
     sa_column_args: Union[Sequence[Any], UndefinedType] = Undefined,
     sa_column_kwargs: Union[Mapping[str, Any], UndefinedType] = Undefined,
     schema_extra: Optional[Dict[str, Any]] = None,
@@ -183,6 +187,7 @@ def Field(
         nullable=nullable,
         index=index,
         sa_column=sa_column,
+        sa_column_type=sa_column_type,
         sa_column_args=sa_column_args,
         sa_column_kwargs=sa_column_kwargs,
         **current_schema_extra,
@@ -412,7 +417,11 @@ def get_column_from_field(field: ModelField) -> Column:
     sa_column = getattr(field.field_info, "sa_column", Undefined)
     if isinstance(sa_column, Column):
         return sa_column
-    sa_type = get_sqlachemy_type(field)
+    sa_column_type = getattr(field.field_info, "sa_column_type", Undefined)
+    if sa_column_type is not Undefined:
+        sa_type = sa_column_type
+    else:
+        sa_type = get_sqlachemy_type(field)
     primary_key = getattr(field.field_info, "primary_key", False)
     nullable = not field.required
     index = getattr(field.field_info, "index", Undefined)