Cast to ObjectId failed for value | Mongodb Error-CodePudding

I'm trying to fetch only the users posts, and i'm using this code:

router.get("/:username", async (req, res) => {
  try {
    const user = await User.findOne({ username: req.params.username });
    const posts = await Post.find({ userId: user._id });
    res.status(200).json(posts);
  } catch (err) {
    res.status(500).json(err);
  }
});

I'm using Postman for testing GET localhost:6000/posts/admin and every time I try it, it gives this error

"name": "CastError",
"message": "Cast to ObjectId failed for value \"admin\" (type string) at path \"_id\" for model \"Post\""

This is my posts collection in Monogodb

And this is the users collection in Mongodb

I don't know what i'm missing here, I just want the link posts/:username shows the posts of this username only

CodePudding user response：

const user = await User.findOne({ username: req.params.username });

This query finds user but user._id comes as object but in your db userId saved as a string so you should probably save userId as object

const blogSchema = new Schema({
    title: {
        type: String,
        required: true,
    },
    content: {
        type: String,
        required: true,
    },
    userId: { type: mongoose.Types.ObjectId, ref: 'user' }, //Example
});

CodePudding user response：

Mongoose's findById method casts the id parameter to the type of the model's _id field so that it can properly query for the matching doc. This is an ObjectId but "foo" is not a valid ObjectId so the cast fails.

This doesn't happen with 41224d776a326fb40f000001 because that string is a valid ObjectId.

One way to resolve this is to add a check prior to your findById call to see if id is a valid ObjectId or not like so:

    if (id.match(/^[0-9a-fA-F]{24}$/)) {
      // Yes, it's a valid ObjectId, proceed with `findById` call.
    }