diff --git a/readme.md b/readme.md
index 57672034..434d2a95 100644
--- a/readme.md
+++ b/readme.md
@@ -27,7 +27,11 @@ export interface TodoEntity extends Entity {
 import factory from '@js-entity-repos/express/dist/factory';
 
 const todosFacade = factory<TodoEntity>({
-  // Optional property that determines the default pagination limit.
+  // Optional property that modifies a filter for the service.
+  constructFilter: (filter) => {
+    return filter;
+  },
+  // Optional property.
   defaultPaginationLimit: 10,
   // Optional property that catches errors from handlers.
   errorCatcher: (handler) => (req, res) => {
diff --git a/src/FacadeConfig.ts b/src/FacadeConfig.ts
index da97650e..e1f7d41e 100644
--- a/src/FacadeConfig.ts
+++ b/src/FacadeConfig.ts
@@ -1,8 +1,10 @@
 import Facade from '@js-entity-repos/core/dist/Facade';
 import Entity from '@js-entity-repos/core/dist/types/Entity';
+import Filter from '@js-entity-repos/core/dist/types/Filter';
 import ErrorCatcher from './utils/ErrorCatcher';
 
 export default interface FacadeConfig<E extends Entity> {
+  readonly constructFilter: (filter: Filter<E>) => any;
   readonly service: Facade<E>;
   readonly errorCatcher: ErrorCatcher;
   readonly defaultPaginationLimit: number;
diff --git a/src/factory.ts b/src/factory.ts
index 1f9d542e..7b397947 100644
--- a/src/factory.ts
+++ b/src/factory.ts
@@ -15,6 +15,7 @@ import catchErrors from './utils/catchErrors';
 
 export default <E extends Entity>(factoryConfig: FactoryConfig<E>): Router => {
   const facadeConfig: FacadeConfig<E> = {
+    constructFilter: (filter) => filter,
     defaultPaginationLimit: 10,
     errorCatcher: catchErrors,
     ...factoryConfig,
diff --git a/src/functions/countEntities.ts b/src/functions/countEntities.ts
index 453c08a8..f75e697e 100644
--- a/src/functions/countEntities.ts
+++ b/src/functions/countEntities.ts
@@ -8,7 +8,7 @@ import getJsonQueryParam from '../utils/getJsonQueryParam';
 export default <E extends Entity>(config: FacadeConfig<E>) => {
   return catchErrors(async (req: Request, res: Response) => {
     const { count } = await config.service.countEntities({
-      filter: getJsonQueryParam(req.query, 'filter'),
+      filter: config.constructFilter(getJsonQueryParam(req.query, 'filter')),
     });
     res.status(OK).json(count);
   });
diff --git a/src/functions/getEntities.ts b/src/functions/getEntities.ts
index 75720e1f..d40202e3 100644
--- a/src/functions/getEntities.ts
+++ b/src/functions/getEntities.ts
@@ -10,7 +10,7 @@ export default <E extends Entity>(config: FacadeConfig<E>) => {
   return catchErrors(async (req: Request, res: Response) => {
     const limit = getNumberQueryParam(req.query, 'limit', config.defaultPaginationLimit);
     const result = await config.service.getEntities({
-      filter: getJsonQueryParam(req.query, 'filter'),
+      filter: config.constructFilter(getJsonQueryParam(req.query, 'filter')),
       pagination: {
         cursor: req.query.cursor,
         forward: req.query.forward === 'true',
diff --git a/src/functions/getEntity.ts b/src/functions/getEntity.ts
index f2262efb..f1aed8a8 100644
--- a/src/functions/getEntity.ts
+++ b/src/functions/getEntity.ts
@@ -8,7 +8,7 @@ import getJsonQueryParam from '../utils/getJsonQueryParam';
 export default <E extends Entity>(config: FacadeConfig<E>) => {
   return catchErrors(async (req: Request, res: Response) => {
     const { entity } = await config.service.getEntity({
-      filter: getJsonQueryParam(req.query, 'filter'),
+      filter: config.constructFilter(getJsonQueryParam(req.query, 'filter')),
       id: req.params.id,
     });
     res.status(OK).json(entity);
diff --git a/src/functions/patchEntities.ts b/src/functions/patchEntities.ts
index 843d2c79..e11e40dd 100644
--- a/src/functions/patchEntities.ts
+++ b/src/functions/patchEntities.ts
@@ -8,7 +8,7 @@ import getJsonQueryParam from '../utils/getJsonQueryParam';
 export default <E extends Entity>(config: FacadeConfig<E>) => {
   return catchErrors(async (req: Request, res: Response) => {
     const { entity } = await config.service.patchEntity({
-      filter: getJsonQueryParam(req.query, 'filter'),
+      filter: config.constructFilter(getJsonQueryParam(req.query, 'filter')),
       id: req.params.id,
       patch: req.body,
     });
diff --git a/src/functions/removeEntities.ts b/src/functions/removeEntities.ts
index 39981ac4..7a0952ae 100644
--- a/src/functions/removeEntities.ts
+++ b/src/functions/removeEntities.ts
@@ -8,7 +8,7 @@ import getJsonQueryParam from '../utils/getJsonQueryParam';
 export default <E extends Entity>(config: FacadeConfig<E>) => {
   return catchErrors(async (req: Request, res: Response) => {
     await config.service.removeEntities({
-      filter: getJsonQueryParam(req.query, 'filter'),
+      filter: config.constructFilter(getJsonQueryParam(req.query, 'filter')),
     });
     res.status(NO_CONTENT).send();
   });
diff --git a/src/functions/removeEntity.ts b/src/functions/removeEntity.ts
index e4af6d08..c9fb7b76 100644
--- a/src/functions/removeEntity.ts
+++ b/src/functions/removeEntity.ts
@@ -8,7 +8,7 @@ import getJsonQueryParam from '../utils/getJsonQueryParam';
 export default <E extends Entity>(config: FacadeConfig<E>) => {
   return catchErrors(async (req: Request, res: Response) => {
     await config.service.removeEntity({
-      filter: getJsonQueryParam(req.query, 'filter'),
+      filter: config.constructFilter(getJsonQueryParam(req.query, 'filter')),
       id: req.params.id,
     });
     res.status(NO_CONTENT).send();
diff --git a/src/functions/replaceEntity.ts b/src/functions/replaceEntity.ts
index 85279b29..f7d5ee38 100644
--- a/src/functions/replaceEntity.ts
+++ b/src/functions/replaceEntity.ts
@@ -9,7 +9,7 @@ export default <E extends Entity>(config: FacadeConfig<E>) => {
   return catchErrors(async (req: Request, res: Response) => {
     const { entity } = await config.service.replaceEntity({
       entity: req.body,
-      filter: getJsonQueryParam(req.query, 'filter'),
+      filter: config.constructFilter(getJsonQueryParam(req.query, 'filter')),
       id: req.params.id,
     });
     res.status(OK).json(entity);
diff --git a/src/utils/getJsonQueryParam.ts b/src/utils/getJsonQueryParam.ts
index 8a093ecd..0c8c4fa9 100644
--- a/src/utils/getJsonQueryParam.ts
+++ b/src/utils/getJsonQueryParam.ts
@@ -3,5 +3,5 @@ import Query from './Query';
 
 export default (data: Query, paramName: string) => {
   const paramValue = data[paramName];
-  return paramValue === undefined ? undefined : parseJson(paramValue, [paramName]);
+  return paramValue === undefined ? {} : parseJson(paramValue, [paramName]);
 };