Merge pull request #58 from ral-facilities/54_use_enum_for_parameter_…

…type

Use enum for parameter type

common/exceptions.py

@@ -1,8 +1,3 @@
-import logging
-
-log = logging.getLogger()
-
-
 class ApiError(Exception):
     pass
 
@@ -21,3 +16,7 @@ class AuthenticationError(ApiError):
 
 class BadRequestError(ApiError):
     pass
+
+
+class DatabaseError(ApiError):
+    pass

common/models/db_models.py

@@ -1,13 +1,41 @@
-from sqlalchemy import Index, Column, BigInteger, String, DateTime, ForeignKey, Integer, Float, FetchedValue
+import enum
+
+from sqlalchemy import Index, Column, BigInteger, String, DateTime, ForeignKey, Integer, Float, FetchedValue, \
+    TypeDecorator
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import relationship
 from sqlalchemy.orm.collections import InstrumentedList
 
-from common.exceptions import BadFilterError
+from common.exceptions import BadFilterError, DatabaseError
 
 Base = declarative_base()
 
 
+class EnumAsInteger(TypeDecorator):
+    """
+    Column type for storing Python enums in a database INTEGER column.
+    """
+    impl = Integer
+
+    def __init__(self, enum_type):
+        super(EnumAsInteger, self).__init__()
+        self.enum_type = enum_type
+
+    def process_bind_param(self, value, dialect):
+        if isinstance(value, self.enum_type):
+            return value.value
+        raise DatabaseError(f"value {value} not in {self.enum_type.__name__}")
+
+    def process_result_value(self, value, dialect):
+        try:
+            return f"{self.enum_type(value)}".replace(f"{self.enum_type.__name__}.", "")  # Strips the enum class name
+        except ValueError:
+            raise DatabaseError(f"value {value} not in {self.enum_type.__name__}")  # This will force a 500 response
+
+    def copy(self, **kwargs):
+        return EnumAsInteger(self.enum_type)
+
+
 class EntityHelper(object):
     """
     EntityHelper class that contains methods to be shared across all entities
@@ -606,6 +634,11 @@ class PARAMETERTYPE(Base, EntityHelper):
         Index('UNQ_PARAMETERTYPE_0', 'FACILITY_ID', 'NAME', 'UNITS'),
     )
 
+    class ValueTypeEnum(enum.Enum):
+        DATE_AND_TIME = 0
+        NUMERIC = 1
+        STRING = 2
+
     ID = Column(BigInteger, primary_key=True)
     APPLICABLETODATACOLLECTION = Column(Integer, server_default=FetchedValue())
     APPLICABLETODATAFILE = Column(Integer, server_default=FetchedValue())
@@ -623,7 +656,7 @@ class PARAMETERTYPE(Base, EntityHelper):
     NAME = Column(String(255), nullable=False)
     UNITS = Column(String(255), nullable=False)
     UNITSFULLNAME = Column(String(255))
-    VALUETYPE = Column(Integer, nullable=False)
+    VALUETYPE = Column(EnumAsInteger(ValueTypeEnum), nullable=False)
     VERIFIED = Column(Integer, server_default=FetchedValue())
     FACILITY_ID = Column(ForeignKey('FACILITY.ID'), nullable=False)