Virtuals as schematypes: validators, type casting, etc.

[mhombach]

Do you want to request a feature or report a bug?
Feature

What is the current behavior?
Virtuals are just functions and not real object which can hold information.

My request:
As other ORM allow (this isn't implying mongoose should always "do what others do"), i am missing the possibility to store additional data on a document on runtime, which isn't saved to the database.
As @vkarpov15 already wrote you can just save data to some attribute called _myAttr and create a virtual getter/setter to access this.
This "works" but in my opinion it would be much more understandable and easier to add a new Attribute-Type "Virtual", which is a property that exists on the document but is never saved to the database.
I could think of something like

tempAttr: { type: Virtual, of: String, required: false }

This way there could be any data stored on the document which can be accessed/changed from multiple sources (parent-code, hooks, validation).

Use-case would be, for example, if i want to have a virtual attribute which contains some calculated value that is processing-intensive (and needs to query the database).
It's not performant to always process and query the needed data everytime it's needed during runtime.
What do you think of this?
If you want to have a look how this could look like, "sequelize" uses this new datatype and i think "TypeORM" does it too.

[x-o1d]

possible use case #7457

[vkarpov15]

There's nothing that stops you from setting arbitrary properties on a doc. doc.foo = 'bar'; does exactly what you expect if foo isn't in the schema, just stores a temporary property on doc that isn't stored in the database.

[mhombach]

@vkarpov15 the pro of making these available as official schema-type would be for example:

• write validators
• give errors of the provided value does not fit the specififcation (string/number/objId)

IMHO this also would be better fitting for an ODM because you can define the clean data-structure within the schema, regardless of what and how data is saved in the end. Is there really no way you could think of such a thing to become real?

[vkarpov15]

Validators for virtuals is an interesting idea. I'll re-open this.