React-GraphQL-Apollo-Mongoose中Mutation传对象数组触发‘Cannot read property 'get' of undefined’错误

Let’s break down what’s going on here: your database operation succeeds, but GraphQL throws an error because Mongoose fails to process the embedded product array when converting the saved document into a GraphQL-compatible response. The error stack points to a virtual property getter on an embedded document trying to call .get() on an undefined value—so the root issue is almost certainly a mismatch between your Mongoose Order model schema and the GraphQL input structure, or a problematic virtual field in your Mongoose schemas.

Step 1: Verify Your Mongoose Order Model Schema #

First, ensure your Mongoose model exactly mirrors the structure you’ve defined in GraphQL. Your GraphQL schema expects product to be an array of objects with prodId and a nested value array—your Mongoose schema needs to use embedded document arrays to match this. Here’s the correct setup:

// Define the nested Value schema first
const ValueSchema = new mongoose.Schema({
  name: String,
  props: String
});

// Define the Product schema (embedded in Order)
const ProductSchema = new mongoose.Schema({
  prodId: String,
  value: [ValueSchema] // Must be a DocumentArray, not a plain array
});

// Define the main Order schema
const OrderSchema = new mongoose.Schema({
  orderId: Number,
  product: [ProductSchema] // Again, use a DocumentArray for embedded products
});

// Create the model
const Order = mongoose.model('Order', OrderSchema);

If your existing model uses plain arrays instead of embedded document schemas, or if field names/types don’t match, Mongoose will struggle to parse incoming data and throw that "get of undefined" error during document conversion.

Step 2: Clean Up Your Resolver Logic #

Your current resolver has redundant code, and adding validation can prevent bad data from reaching Mongoose. Update it to:

addOrder(parent, args, context, info) {
  const updateData = {};

  // Only add fields if they're provided and valid
  if (args.orderId !== undefined) {
    updateData.orderId = args.orderId;
  }
  if (args.product && Array.isArray(args.product)) {
    // Filter out invalid product entries to avoid Mongoose parsing issues
    updateData.product = args.product.filter(prod => prod && prod.prodId);
  }

  return context.Order.findOneAndUpdate(
    { orderId: args.orderId },
    { $setOnInsert: updateData },
    { 
      new: true, 
      upsert: true,
      runValidators: true // Critical: ensures data matches your Mongoose schema
    }
  );
}

The runValidators: true flag is key—it makes Mongoose validate the incoming product array against your schema before insertion, catching mismatches early instead of letting them cause cryptic errors later.

Step 3: Check for Problematic Virtual Fields #

If you’ve defined virtual properties in your Product or Value Mongoose schemas, double-check their getter functions. For example, a virtual like this would cause exactly the error you’re seeing:

// Bad example—fails if `someProperty` is undefined
ProductSchema.virtual('customField').get(function() {
  return this.someProperty.get();
});

Fix virtual getters to guard against undefined values:

// Fixed version
ProductSchema.virtual('customField').get(function() {
  return this.someProperty ? this.someProperty.get() : null;
});

Testing the Fix #

After updating your Mongoose schema and resolver, re-run your mutation with a product array. The error should disappear, and GraphQL will return the saved Order object correctly—Mongoose can now properly process the embedded document array without hitting undefined properties.

内容的提问来源于stack exchange，提问作者Mike Will