How Can I Evaluate JavaScript to Dynamically Assign Field Values in MongoDB?

MongoDB: Evaluating JavaScript for Field Values

In MongoDB, you can dynamically assign values to document fields using JavaScript. However, you encountered an issue where a helper function intended to return the current time was stored as a script instead of being evaluated.

Stored JavaScript Functions

To have JavaScript evaluated on the server-side, you need to store the function in the system.js collection. This collection holds JavaScript functions that can be reused.

Go Driver Implementation

To call a stored JavaScript function from Go using the mgo driver, use the Run() method and issue an eval command with the function's name as the argument. For example:

err := db.Run(bson.M{"eval": "myStoredFunction();"})

Note that JavaScript evaluation is not supported in MongoDB insert statements. Therefore, you must insert the field value as a literal or use a stored JavaScript function.

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