fix(core): allow filter condition callbacks without arguments

Closes #847

docs/docs/filters.md

@@ -59,6 +59,23 @@ const books = await orm.em.find(Book, {}, {
 });
 ```
 
+### Filters without parameters
+
+If we want to have a filter condition that do not need arguments, but we want
+to access the `type` parameter, we will need to explicitly set `args: false`, 
+otherwise error will be raised due to missing parameters:
+
+```ts
+@Filter({
+  name: 'withoutParams',
+  cond(_, type) {
+    return { ... };
+  },
+  args: false,
+  default: true,
+})
+```
+
 ## Global filters
 
 We can also register filters dynamically via `EntityManager` API. We call such filters 

docs/versioned_docs/version-4.0/filters.md

@@ -59,6 +59,23 @@ const books = await orm.em.find(Book, {}, {
 });
 ```
 
+### Filters without parameters
+
+If we want to have a filter condition that do not need arguments, but we want
+to access the `type` parameter, we will need to explicitly set `args: false`, 
+otherwise error will be raised due to missing parameters:
+
+```ts
+@Filter({
+  name: 'withoutParams',
+  cond(_, type) {
+    return { ... };
+  },
+  args: false,
+  default: true,
+})
+```
+
 ## Global filters
 
 We can also register filters dynamically via `EntityManager` API. We call such filters 

packages/core/src/EntityManager.ts

@@ -157,7 +157,7 @@ export class EntityManager<D extends IDatabaseDriver = IDatabaseDriver> {
       if (filter.cond instanceof Function) {
         const args = Utils.isPlainObject(options[filter.name]) ? options[filter.name] : this.filterParams[filter.name];
 
-        if (!args && filter.cond.length > 0) {
+        if (!args && filter.cond.length > 0 && filter.args !== false) {
           throw new Error(`No arguments provided for filter '${filter.name}'`);
         }
 

packages/core/src/typings.ts

@@ -252,6 +252,7 @@ export type FilterDef<T extends AnyEntity<T>> = {
   cond: FilterQuery<T> | ((args: Dictionary, type: 'read' | 'update' | 'delete') => FilterQuery<T> | Promise<FilterQuery<T>>);
   default?: boolean;
   entity?: string[];
+  args?: boolean;
 };
 
 export type ExpandProperty<T> = T extends Reference<infer U> ? NonNullable<U> : T extends Collection<infer U> ? NonNullable<U> : NonNullable<T>;

tests/entities/Author.ts

@@ -11,9 +11,11 @@ import { BaseEntity } from './BaseEntity';
 @Index({ name: 'custom_idx_1', properties: ['name', 'email'] })
 @Filter({
   name: 'withoutParams1',
-  cond() {
+  cond(_, type) {
+    expect(['read', 'update', 'delete'].includes(type)).toBe(true);
     return {};
   },
+  args: false,
   default: true,
 })
 export class Author extends BaseEntity<Author> {