typesafe post edit with author checking

src/api/posts/edit.ts

@@ -0,0 +1,22 @@
+import { Post } from '@/models/PostModel';
+import { editPost } from '@/controller/PostController';
+import { Post as PrismaPost } from '@prisma/client';
+import { Request, Response } from 'express';
+
+export default async (req: Request, res: Response) => {
+  try {
+    const post: Post = Post.parse(req.body);
+    const userId = 1; // hardcoded for now, use userId from token
+    const editedPost: PrismaPost | null | Error = await editPost(post, userId);
+    if (editedPost === null) {
+      return res.status(404).send('Post not found');
+    }
+    if (editedPost instanceof Error) {
+      return res.status(403).send(editedPost.message);
+    }
+
+    return res.status(200).send(editedPost);
+  } catch (error) {
+    return res.status(500).send(error);
+  }
+};

src/controller/PostController.ts

@@ -10,6 +10,15 @@ const exclude = <User, Key extends keyof User>(user: User, ...keys: Key[]): User
   return user;
 };
 
+const getPostById = async (id: number): Promise<PrismaPost | null> => {
+  const post = await prisma.post.findUnique({
+    where: {
+      id,
+    },
+  });
+  return post;
+};
+
 const getAllPosts = async (): Promise<PrismaPost[]> => {
   const posts = prisma.post.findMany({
     include: {
@@ -35,4 +44,33 @@ const createPost = async (post: Post): Promise<PrismaPost> => {
   return newPost;
 };
 
-export { getAllPosts, createPost };
+const editPost = async (post: Post, userId: number): Promise<PrismaPost | null | Error> => {
+  if (post.id === undefined) {
+    return new Error('Post id is undefined');
+  }
+  const originalPost = await getPostById(post.id);
+  if (originalPost === null) {
+    return null;
+  }
+  if (originalPost.authorId !== userId) {
+    return new Error('User is not the author of this post');
+  }
+  const editedPost = await prisma.post.update({
+    where: {
+      id: post.id,
+    },
+    data: {
+      title: post.title,
+      content: post.content,
+      image: post.image,
+    },
+  });
+
+  if (!editedPost) {
+    return null;
+  }
+
+  return editedPost;
+};
+
+export { getAllPosts, createPost, editPost };

src/models/PostModel.ts

@@ -1,7 +1,7 @@
 import { z } from 'zod';
 
 interface Post {
-  id?: number | null;
+  id?: number | undefined;
   title: string;
   content?: string | undefined;
   image?: string | undefined;