Mikey P Mikey P - 1 year ago 253
Node.js Question

How to work with async code in Mongoose virtual properties?

I'm trying to work with associating documents in different collections (not embedded documents) and while there is an issue for that in Mongooose, I'm trying to work around it now by lazy loading the associated document with a virtual property as documented on the Mongoose website.

The problem is that the getter for a virtual takes a function as an argument and uses the return value for the virtual property. This is great when the virtual doesn't require any async calls to calculate it's value, but doesn't work when I need to make an async call to load the other document. Here's the sample code I'm working with:

.get( function() { // <-- the return value of this function is used as the property value
Notebook.findById(this.notebookId, function(err, notebook) {
return notebook; // I can't use this value, since the outer function returns before we get to this code
// undefined is returned here as the properties value

This doesn't work since the function returns before the async call is finished. Is there a way I could use a flow control library to make this work, or could I modify the first function so that I pass the findById call to the getter instead of an anonymous function?

Answer Source

You can define a virtual method, for which you can define a callback.

Using your example:

TransactionSchema.method('getNotebook', function(cb) {
  Notebook.findById(this.notebookId, function(err, notebook) {

And while the sole commenter appears to be one of those pedantic types, you also should not be afraid of embedding documents. Its one of mongos strong points from what I understand.

One uses the above code like so:

    // hey man, I have my notebook and stuff
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