fix: 🐛 deep merge nested rule relations

src/applyRuleRelationsQuery.ts

@@ -3,6 +3,7 @@ import { rulesToAST } from '@casl/ability/extra';
 import { createPrismaAbility, PrismaQuery } from '@casl/prisma';
 import { Prisma } from '@prisma/client';
 import { convertCreationTreeToSelect, CreationTree } from './convertCreationTreeToSelect';
+import { deepMerge } from './deepMerge';
 import { getRuleRelationsQuery } from './getRuleRelationsQuery';
 import { relationFieldsByModel } from './helpers';
 
@@ -174,10 +175,10 @@ function getNestedQueryRelations(args: any, abilities: PureAbility<AbilityTuple,
             const relationField = relationFieldsByModel[model][relation]
 
             if (relationField) {
-              const nestedQueryRelations = {
-                ...getNestedQueryRelations(args[method][relation], abilities, action === 'all' ? 'all' : 'read', relationField.type as Prisma.ModelName),
-                ...(queryRelations[relation]?.select ?? {})
-              }
+              const nestedQueryRelations = deepMerge(
+                getNestedQueryRelations(args[method][relation], abilities, action === 'all' ? 'all' : 'read', relationField.type as Prisma.ModelName),
+                (typeof queryRelations[relation]?.select === 'object' ? queryRelations[relation]?.select : {})
+              )
               if (nestedQueryRelations && Object.keys(nestedQueryRelations).length > 0) {
                 queryRelations[relation] = {
                   ...(queryRelations[relation] ?? {}),

src/deepMerge.ts

@@ -0,0 +1,32 @@
+/**
+ * Simple object check.
+ * @param item
+ * @returns {boolean}
+ */
+export function isObject(item: any) {
+  return (item && typeof item === 'object' && !Array.isArray(item));
+}
+
+/**
+ * https://stackoverflow.com/questions/27936772/how-to-deep-merge-instead-of-shallow-merge
+ * Deep merge two objects.
+ * @param target
+ * @param ...sources
+ */
+export function deepMerge(target: any, ...sources: any[]) {
+  if (!sources.length) return target;
+  const source = sources.shift();
+
+  if (isObject(target) && isObject(source)) {
+    for (const key in source) {
+      if (isObject(source[key])) {
+        if (!target[key]) Object.assign(target, { [key]: {} });
+        deepMerge(target[key], source[key]);
+      } else {
+        Object.assign(target, { [key]: source[key] });
+      }
+    }
+  }
+
+  return deepMerge(target, ...sources);
+}