Document must have an _id before saving

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When dealing with MongoDB, the “document must have an _id before saving” error occurs when trying to save a document without providing a value for the “_id” field. This error is thrown because MongoDB requires every document to have a unique identifier, which is usually set to the “_id” field.

To resolve this error, you need to ensure that the document you are trying to save contains an “_id” field with a unique value. You can manually set the “_id” field before saving, or let MongoDB generate a unique value for you.

Manually setting _id

You can manually set the “_id” field by providing a unique value of your choice. For example:

      {
        "_id": "uniqueId123",
        "name": "John Doe",
        "age": 30
      }

In this case, the document will be saved with “_id” value set to “uniqueId123”.

Letting MongoDB generate _id

If you don’t explicitly set the “_id” field, MongoDB will automatically generate a unique identifier for you. For example:

      {
        "name": "Jane Smith",
        "age": 25
      }

In this case, MongoDB will add an “_id” field with a unique value to the document before saving it.

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In the above code snippet, the answer is wrapped within a `

` tag. It starts with two paragraphs explaining the cause of the error and the requirement of having an “_id” field. Then, it provides two different solutions for resolving the error – manually setting the “_id” and letting MongoDB generate it automatically. Each solution is explained with an example document. The headers are included using `

` tags for better organization and readability.

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