How do I add a Firestore document with DocumentReference fields in Flutter?

Below is an approach to troubleshoot and fix the issue when storing references:

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Verify the DocumentReference Values

Make sure the references themselves are valid. For example, check that

• _selectedBrand is not null.
• _activeCategory.toList() isn’t empty.
• Both items are coming from the same Firestore instance (or constructed the same way).

Print or log the values before saving:

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print('Brand Reference: ${_selectedBrand!.reference}');
print('Category Reference: ${_activeCategory.toList()[0].doc.reference}');

This helps verify that the references actually point to the expected locations.

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Confirm the Map is Correct

Since Firestore accepts DocumentReference types as field values, your conversion to a Map should work as long as the fields are non-null. For example, your toMap() method is correct:

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Map<String, dynamic> toMap() {
  return {
    'name': name,
    'ean': ean,
    'brand': brand,
    'category': category,
  };
}

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Check the Firestore Service Implementation

If your custom _firestoreService.addDocument method isn’t handling DocumentReference fields properly (or if it was built with the assumption that fields are simple types), it might cause the app to close. Verify this method is a wrapper around the standard Firestore API (such as using addDoc or set).

For example, using the modular API directly:

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import 'package:cloud_firestore/cloud_firestore.dart';

Future<void> addProduct(Products product) async {
  try {
    await FirebaseFirestore.instance
        .collection('products')
        .doc(product.name)  // or use auto-generated ID if preferred
        .set(product.toMap());
    print('Product successfully added');
  } catch (e) {
    print('Error adding document: $e');
    // Optionally rethrow or handle the error
  }
}

Testing using the vanilla Firestore call can help narrow down if the issue is in your service wrapper.

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Confirm Exception Handling

Even if you have try/catch in the async method, if an exception occurs outside of that (for example, in building the data) it might crash the application. Make sure you surround all possible null-unsafe access with proper checks.

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Summary

1. Verify that both _selectedBrand and _activeCategory provide valid DocumentReference values.
2. Ensure your custom addDocument method correctly passes the Map (with DocumentReference objects) to Firestore.
3. Add logging to pinpoint if the error occurs before or during the Firestore operation.

If after these checks the app still closes without a visible error, consider using more detailed debug logs or breakpoints to see where the failure occurs.

Let me know if you need more help troubleshooting!