fix: fallback limit-skip-logic when used last and before args without sorting

Related graphql-compose/graphql-compose-mongoose#120
Related #7

Author: nodkz

src/__tests__/github-issues/graphql-compose-mongoose-120-test.js

@@ -11,7 +11,7 @@ describe('check last/before args', () => {
     sort: sortOptions,
   });
 
-  it('should use defaultLimit option', async () => {
+  it('with sort arg', async () => {
     const res1 = await defaultResolver.resolve({
       args: {
         last: 2,
@@ -36,4 +36,28 @@ describe('check last/before args', () => {
       { cursor: 'eyJpZCI6MTN9', node: { age: 45, gender: 'f', id: 13, name: 'user13' } },
     ]);
   });
+
+  it('without sort arg', async () => {
+    const res1 = await defaultResolver.resolve({
+      args: {
+        last: 2,
+        before: '',
+      },
+    });
+    expect(res1.edges).toEqual([
+      { cursor: 'MTM=', node: { age: 45, gender: 'm', id: 14, name: 'user14' } },
+      { cursor: 'MTQ=', node: { age: 45, gender: 'f', id: 13, name: 'user13' } },
+    ]);
+
+    const res2 = await defaultResolver.resolve({
+      args: {
+        last: 2,
+        before: 'MTM=',
+      },
+    });
+    expect(res2.edges).toEqual([
+      { cursor: 'MTE=', node: { age: 47, gender: 'f', id: 12, name: 'user12' } },
+      { cursor: 'MTI=', node: { age: 45, gender: 'm', id: 15, name: 'user15' } },
+    ]);
+  });
 });

src/connectionResolver.js

@@ -152,10 +152,9 @@ export function prepareConnectionResolver(
         description: 'Sort argument for data ordering',
       },
     },
-    // eslint-disable-next-line
-    resolve: async /* :: <TContext> */(
-      resolveParams/* : $Shape<ConnectionResolveParams<TContext>> */
-    ) => {
+    async resolve /* :: <TContext> */(
+      resolveParams /* : $Shape<ConnectionResolveParams<TContext>> */
+    ) {
       let countPromise;
       let findManyPromise;
       const { projection = {}, args, rawQuery } = resolveParams;
@@ -381,7 +380,9 @@ export function prepareLimitSkipFallback(
       newSkip = skip + afterSkip;
     }
   } else if (beforeSkip) {
-    newSkip = skip - beforeSkip;
+    // just simple backward listing (without after arg)
+    // so we simple take previous records reducing skip by limit value
+    newSkip = beforeSkip - limit;
     if (newSkip < 0) {
       newSkip = 0;
       newLimit = limit;