How to add a new column/key in mongodb at run time?

@dana 

In MongoDB, you can add a new field/column to a document in a collection by using the update method with the $set operator. Here's how you can add a new column/key in MongoDB at runtime:

1. Connect to MongoDB using a client like the MongoDB shell or a MongoDB driver for your programming language.
2. Select the database and collection where you want to add a new column/key.
3. Use the update method with the $set operator to add the new field/column to the document. Here's an example using the MongoDB shell:

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db.collection.update({ _id: ObjectId("document_id") }, { $set: { new_column: "new_value" }})

Replace collection with the name of your collection, document_id with the ID of the document you want to update, new_column with the name of the new field/column, and new_value with the value you want to set for the new field/column.

1. The above command will add a new field/column to the document with the specified value. You can also add multiple fields/columns by specifying more key-value pairs in the $set operator.
2. If you want to add a new column/key to multiple documents in a collection, you can use the updateMany method instead. Here's an example:

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db.collection.updateMany({ }, { $set: { new_column: "new_value" }})

This will add the new field/column to all documents in the collection with the specified value.

Please note that if the field/column you are trying to add already exists in the document, the $set operator will update the value of the existing field/column instead of adding a new one.