Got it, let's fix this together! You already have the logic to add exercises to the array, so we just need to tweak that update operation to set previousWeight to 0 at the same time. Here are a couple of straightforward approaches:

1. Directly Include $set in Your Update Query #

This is the simplest way—just add a $set clause right alongside your $push when updating the document. Let's assume your Mongoose model looks something like this first:

// Example User Schema
const UserSchema = new mongoose.Schema({
  exercises: [{
    name: String,
    weight: Number,
    // other exercise fields...
  }],
  previousWeight: Number
});

const User = mongoose.model('User', UserSchema);

Then modify your existing update code to include the $set for previousWeight:

const userId = "your-user-id-here";
const newExercise = { name: "Squats", weight: 120 };

User.findOneAndUpdate(
  { _id: userId },
  {
    $push: { exercises: newExercise }, // Your existing exercise push
    $set: { previousWeight: 0 } // Sync set to 0
  },
  { new: true, runValidators: true } // Return updated doc + enforce schema rules
)
.then(updatedUser => console.log("Updated user:", updatedUser))
.catch(err => console.error("Update error:", err));

This ensures every time you add an exercise, previousWeight gets set to 0 immediately.

2. Use a Mongoose Pre-Hook for Automatic Sync #

If you want this behavior to happen automatically every time an exercise is added (without writing $set every time), you can add a pre-update hook to your schema:

UserSchema.pre("findOneAndUpdate", function(next) {
  // Check if we're pushing a new exercise
  if (this._update.$push && this._update.$push.exercises) {
    // Ensure $set exists, then set previousWeight to 0
    this._update.$set = this._update.$set || {};
    this._update.$set.previousWeight = 0;
  }
  next();
});

Now any findOneAndUpdate call that pushes to the exercises array will automatically set previousWeight to 0—no extra code needed in your update logic!

Quick Notes: #

• If previousWeight might already have a value, this will overwrite it—make sure that's the behavior you want.
• If your schema has validations for previousWeight (like required: true), adding runValidators: true in the update options ensures the 0 value passes those checks.

内容的提问来源于stack exchange，提问作者Gromit