#119: Allow entity objects to be fetched from plural field names

- This feature will be needed when there's camelCase field names for related entities, e.g. for user input on include filters
- This change also moves the location of get_entity_object_from_name() to prevent any issues with circular imports. Since the function no longer makes use of globals(), there's no requirement for the function to be in models.py

datagateway_api/common/database/backend.py

@@ -19,9 +19,9 @@
     requires_session_id,
     update_row_from_id,
 )
-from datagateway_api.common.database.models import EntityHelper, SESSION
+from datagateway_api.common.database.models import SESSION
 from datagateway_api.common.exceptions import AuthenticationError
-from datagateway_api.common.helpers import queries_records
+from datagateway_api.common.helpers import get_entity_object_from_name, queries_records
 
 
 log = logging.getLogger()
@@ -63,49 +63,49 @@ def logout(self, session_id):
     @requires_session_id
     @queries_records
     def get_with_filters(self, session_id, entity_type, filters):
-        table = EntityHelper.get_entity_object_from_name(entity_type)
+        table = get_entity_object_from_name(entity_type)
         return get_rows_by_filter(table, filters)
 
     @requires_session_id
     @queries_records
     def create(self, session_id, entity_type, data):
-        table = EntityHelper.get_entity_object_from_name(entity_type)
+        table = get_entity_object_from_name(entity_type)
         return create_rows_from_json(table, data)
 
     @requires_session_id
     @queries_records
     def update(self, session_id, entity_type, data):
-        table = EntityHelper.get_entity_object_from_name(entity_type)
+        table = get_entity_object_from_name(entity_type)
         return patch_entities(table, data)
 
     @requires_session_id
     @queries_records
     def get_one_with_filters(self, session_id, entity_type, filters):
-        table = EntityHelper.get_entity_object_from_name(entity_type)
+        table = get_entity_object_from_name(entity_type)
         return get_first_filtered_row(table, filters)
 
     @requires_session_id
     @queries_records
     def count_with_filters(self, session_id, entity_type, filters):
-        table = EntityHelper.get_entity_object_from_name(entity_type)
+        table = get_entity_object_from_name(entity_type)
         return get_filtered_row_count(table, filters)
 
     @requires_session_id
     @queries_records
     def get_with_id(self, session_id, entity_type, id_):
-        table = EntityHelper.get_entity_object_from_name(entity_type)
+        table = get_entity_object_from_name(entity_type)
         return get_row_by_id(table, id_).to_dict()
 
     @requires_session_id
     @queries_records
     def delete_with_id(self, session_id, entity_type, id_):
-        table = EntityHelper.get_entity_object_from_name(entity_type)
+        table = get_entity_object_from_name(entity_type)
         return delete_row_by_id(table, id_)
 
     @requires_session_id
     @queries_records
     def update_with_id(self, session_id, entity_type, id_, data):
-        table = EntityHelper.get_entity_object_from_name(entity_type)
+        table = get_entity_object_from_name(entity_type)
         return update_row_from_id(table, id_, data)
 
     @requires_session_id

datagateway_api/common/database/filters.py

@@ -12,6 +12,7 @@
     SkipFilter,
     WhereFilter,
 )
+from datagateway_api.common.helpers import get_entity_object_from_name
 
 
 log = logging.getLogger()
@@ -65,9 +66,8 @@ def apply_filter(self, query):
                 included_included_table,
             )
             field = getattr(included_included_table, self.included_included_field)
-
         elif self.included_field:
-            included_table = getattr(models, self.field)
+            included_table = get_entity_object_from_name(self.field)
             query.base_query = query.base_query.join(included_table)
             field = getattr(included_table, self.included_field)
 

datagateway_api/common/database/models.py

@@ -20,7 +20,7 @@
 from sqlalchemy.orm import relationship
 from sqlalchemy.orm.collections import InstrumentedList
 
-from datagateway_api.common.exceptions import ApiError, DatabaseError, FilterError
+from datagateway_api.common.exceptions import DatabaseError, FilterError
 
 Base = declarative_base()
 
@@ -58,25 +58,6 @@ class EntityHelper(ABC):
     EntityHelper class that contains methods to be shared across all entities
     """
 
-    @staticmethod
-    def get_entity_object_from_name(entity_name):
-        """
-        From an entity name, this function gets a Python version of that entity for the
-        database backend
-
-        :param entity_name: Name of the entity to fetch a version from this model
-        :type entity_name: :class:`str`
-        :return: Object of the entity requested (e.g.
-            :class:`datagateway_api.common.database.models.INVESTIGATIONINSTRUMENT`)
-        :raises: KeyError: If an entity model cannot be found as a class in this model
-        """
-        try:
-            return globals()[entity_name.upper()]
-        except KeyError:
-            raise ApiError(
-                f"Entity class cannot be found, missing class for {entity_name}",
-            )
-
     def to_dict(self):
         """
         Turns the columns and values of an entity into a dictionary

datagateway_api/common/helpers.py

@@ -6,6 +6,7 @@
 from flask_restful import reqparse
 from sqlalchemy.exc import IntegrityError
 
+from datagateway_api.common.database import models
 from datagateway_api.common.exceptions import (
     ApiError,
     AuthenticationError,
@@ -101,3 +102,27 @@ def get_filters_from_query_string():
         return filters
     except Exception as e:
         raise FilterError(e)
+
+
+def get_entity_object_from_name(entity_name):
+    """
+    From an entity name, this function gets a Python version of that entity for the
+    database backend
+
+    :param entity_name: Name of the entity to fetch a version from this model
+    :type entity_name: :class:`str`
+    :return: Object of the entity requested (e.g.
+        :class:`datagateway_api.common.database.models.INVESTIGATIONINSTRUMENT`)
+    :raises: KeyError: If an entity model cannot be found as a class in this model
+    """
+    try:
+        # If a plural is given, fetch the singular field name
+        if entity_name[-1] == "s":
+            entity_name = entity_name[0].upper() + entity_name[1:]
+            entity_name = endpoints[entity_name]
+
+        return getattr(models, entity_name.upper())
+    except KeyError:
+        raise ApiError(
+            f"Entity class cannot be found, missing class for {entity_name}",
+        )

datagateway_api/src/resources/entities/entity_map.py

@@ -2,6 +2,7 @@
 
 from sqlalchemy.inspection import inspect
 
+from datagateway_api.common.helpers import get_entity_object_from_name
 from datagateway_api.src.resources.entities.entity_endpoint_dict import endpoints
 
 
@@ -36,7 +37,7 @@ def create_entity_models():
     for endpoint in endpoints:
         params = {}
         required = []
-        endpoint_table = EntityHelper.get_entity_object_from_name(endpoints[endpoint])
+        endpoint_table = get_entity_object_from_name(endpoints[endpoint])
         endpoint_inspection = inspect(endpoint_table)
         for column in endpoint_inspection.columns:
             # Needed to ensure camelCase field names are used, rather than SNAKE_CASE