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Description

MongoDB Error 211, "Key Not Found", indicates that an operation attempted to access or modify data using a key, _id, or index entry that does not exist within the specified collection or index. This typically occurs during read, update, or delete operations when the target data cannot be located.

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Error Message

Key Not Found

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Known Causes

3 known causes

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Document Not Found

The query attempted to retrieve, update, or delete a document using an _id or specific key that does not exist in the collection.

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Incorrect Index Usage

An operation tried to utilize an index key that is not present, valid, or correctly defined for the specified index.

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Typo or Mismatch in Key/ID

The provided key, _id, or field name in the query contains a typo, incorrect casing, or does not exactly match the stored data.

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Solutions

4 solutions available

1. Check _id Value easy

Verify document with _id exists

1

Check if document exists

db.collection.findOne({ _id: ObjectId("...") })

2

List some documents

db.collection.find().limit(5)

2. Fix ObjectId Format easy

Ensure correct ObjectId type

1

Convert string to ObjectId

// Wrong:
db.collection.findOne({ _id: "507f1f77bcf86cd799439011" })

// Right:
db.collection.findOne({ _id: ObjectId("507f1f77bcf86cd799439011") })

2

Validate ObjectId string

// Check if valid 24-char hex string
const isValid = /^[0-9a-fA-F]{24}$/.test(idString);

3. Check Index Exists easy

For index operations, verify index exists

1

List indexes

db.collection.getIndexes()

2

Drop with correct name

db.collection.dropIndex("index_name")

4. Handle Document Deletion Race medium

Document deleted between find and update

1

Use findOneAndUpdate atomically

const result = db.collection.findOneAndUpdate(
  { _id: ObjectId("...") },
  { $set: { status: "updated" } },
  { returnNewDocument: true }
);

if (!result) {
  console.log("Document not found");
}

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Related Errors

5 related errors

MongoDB Error 211: Key Not Found Error