EC
2
MongoDBERRORNotableWrite ErrorHIGH confidence

Invalid BSON field value provided

What this means

This error occurs when an operation attempts to use a value of an incorrect or unsupported BSON type for a field. MongoDB's strict schema validation or data type constraints trigger this error when the provided data does not match the expected format.

Why it happens
  1. 1Providing a string where a number is expected in a document field, or vice-versa
  2. 2Using an unsupported data type like 'undefined' in a document field, which is not a valid BSON type
  3. 3Attempting to update a field with a value that violates a collection's defined schema validation rules
  4. 4Corrupted data being sent from the application layer due to a bug or incorrect data manipulation
How to reproduce

An update operation tries to set a field to an invalid BSON type, such as `undefined`.

trigger — this will error
trigger — this will error
db.products.insertOne({ sku: "123-abc", price: 99.99 });
// The following update fails because 'undefined' is not a valid BSON type for a field value.
db.products.updateOne({ sku: "123-abc" }, { $set: { description: undefined } });

expected output

MongoServerError: BSON field 'update.$set.description' is the wrong type 'undefined', expected types...

Fix 1

Sanitize Input and Use Correct Data Types

WHEN Always before performing any write or update operation.

Sanitize Input and Use Correct Data Types
// Correct: Use null to represent an empty or non-existent value.
db.products.updateOne(
  { sku: "123-abc" },
  { $set: { description: null } }
);

Why this works

Always validate and sanitize application input to ensure all fields conform to valid BSON data types. Using `null` is the correct BSON-compatible way to represent a non-value, whereas JavaScript's `undefined` is not.

Fix 2

Implement Stricter Schema Validation

WHEN When you need to enforce data integrity and consistency at the database level.

Implement Stricter Schema Validation
db.createCollection("products", {
  validator: {
    $jsonSchema: {
      bsonType: "object",
      required: ["sku", "price"],
      properties: {
        sku: { bsonType: "string" },
        price: { bsonType: "double" },
        description: { bsonType: ["string", "null"] }
      }
    }
  }
})

Why this works

MongoDB's server-side schema validation feature rejects any insert or update operations that do not meet the specified criteria, preventing BadValue errors from occurring at the source and ensuring data quality.

What not to do

✕ Remove or disable schema validation just to force a write operation through

Disabling validation rules undermines data consistency, pollutes the collection with malformed documents, and inevitably leads to more complex, data-related bugs in the application logic.

Sources
Official documentation ↗

mongodb/mongo src/mongo/base/error_codes.yml

BSON Types ↗

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