fix: changes empty result query to be $expr with object, otherwise mongoose throws error

But mongo works OK with `{ $expr: false }` however official docs says it should be an object

Author: stalniy

packages/casl-mongoose/spec/accessibleBy.spec.ts

@@ -16,7 +16,7 @@ describe('accessibleBy', () => {
 
     const query = accessibleBy(ability, 'update').Post
 
-    expect(query).toEqual({ $expr: false })
+    expect(query).toEqual({ $expr: { $eq: [0, 1] } })
   })
 
   it('returns `{ $expr: false }` if there is a rule that forbids previous one', () => {
@@ -27,7 +27,7 @@ describe('accessibleBy', () => {
 
     const query = accessibleBy(ability, 'update').Post
 
-    expect(query).toEqual({ $expr: false })
+    expect(query).toEqual({ $expr: { $eq: [0, 1] } })
   })
 
   describe('it behaves like `toMongoQuery` when converting rules', () => {

packages/casl-mongoose/src/accessible_records.ts

@@ -1,14 +1,14 @@
 import { Normalize, AnyMongoAbility, Generics, ForbiddenError } from '@casl/ability';
 import { Schema, QueryWithHelpers, Model, Document, HydratedDocument, Query } from 'mongoose';
-import { toMongoQuery } from './mongo';
+import { EMPTY_RESULT_QUERY, toMongoQuery } from './mongo';
 
 function failedQuery(
   ability: AnyMongoAbility,
   action: string,
   modelName: string,
   query: QueryWithHelpers<Document, Document>
 ) {
-  query.where({ $expr: false }); // rule that returns empty result set
+  query.where(EMPTY_RESULT_QUERY);
   const anyQuery: any = query;
 
   if (typeof anyQuery.pre === 'function') {

packages/casl-mongoose/src/mongo.ts

@@ -37,9 +37,10 @@ export function accessibleBy<T extends AnyMongoAbility>(
   }, accessibleByProxyHandlers) as unknown as Record<StringOrKeysOf<RecordTypes>, AbilityQuery>;
 }
 
+export const EMPTY_RESULT_QUERY = { $expr: { $eq: [0, 1] } };
 const accessibleByProxyHandlers: ProxyHandler<{ _ability: AnyMongoAbility, _action: string }> = {
   get(target, subjectType) {
     const query = rulesToQuery(target._ability, target._action, subjectType, convertToMongoQuery);
-    return query === null ? { $expr: false } : query;
+    return query === null ? EMPTY_RESULT_QUERY : query;
   }
 };