Mongooseerror: document must have an _id before saving

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The error message “document must have an _id before saving” is a common error in Mongoose, which occurs when attempting to save a document that does not have a value for the required “_id” field. Every Mongoose document requires an “_id” field, which serves as a unique identifier for the document.

To resolve this error, you need to ensure that your document has an “_id” value before saving it. There are a couple of ways to achieve this:

1. Manually assign an _id:

You can manually assign an “_id” value to your document before saving it. The “_id” value can be a string or a number: 

// Example using a string _id
const exampleSchema = new mongoose.Schema({
  _id: String,
  name: String,
  age: Number
});

const ExampleModel = mongoose.model('Example', exampleSchema);

const example = new ExampleModel({
  _id: 'example-id-1',
  name: 'John Doe',
  age: 30
});

example.save();

2. Let Mongoose automatically generate the _id:

If you don’t provide an “_id” value, Mongoose will automatically generate a unique “_id” for your document. You can achieve this by omitting the “_id” field in the document creation: 

const exampleSchema = new mongoose.Schema({
  name: String,
  age: Number
});

const ExampleModel = mongoose.model('Example', exampleSchema);

const example = new ExampleModel({
  name: 'John Doe',
  age: 30
});

example.save();

In the second example, Mongoose will generate a unique “_id” for the “example” document before saving it.

Make sure to choose the appropriate method based on your requirements. If you have a specific identifier for your documents, you can manually assign the “_id” field. Otherwise, you can let Mongoose handle the generation of a unique “_id” automatically.

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