Add `enum` type

[Didas-git]

I saw this issue on the official redis-om repository (here: redis/redis-om-node#86) and got a bit confused.

Today while writing some code i got an idea on how to do it that i will probably implement in the future:

// create a enum on the schema
somefield: {
    type: "enum",
    fields: [
        "FieldWithValue0",
        "FieldWithValue1",
        // You could also use strings as values
        { FieldWithValue300: 300 },
        "FieldWithValue301"
    ]
}

// using it (this is the complicated part)
// the database would return a number which would need to be mapped back

const data = await model.get(someId)
data.somefield // this is a number (lets say 1 for the sake of the example)

// this is how you would map it back
model.enums.somefield[data.somefield] // returns "FieldWithValue1"

[Didas-git]

There are also other alternatives.
One that comes to mind is:

const data = await model.get(someId);

data.somefield.$value // returns the actuall value in the db
data.somefield.FieldWithValue0 // returns 0
data.somefield[data.somefield.$value] // returns the string equivalent to the number aka the enum field

This is duable but however it could have some impact in both performance and memory if you are using enums with more than 30~50 fields/elements in it

[timolson]

Consider making this more generic, to support any kind of user-extended types. For example, I'm re-wrapping the ORM object in order to provide conversion of bigints to/from strings.

[Didas-git]

Consider making this more generic, to support any kind of user-extended types. For example, I'm re-wrapping the ORM object in order to provide conversion of bigints to/from strings.

There are some issues when it comes to making it more generic, the main one being handling parsing for said user extended types thats something i never planed for and would need some discussion about.

The current problem im facing regarding enum implementation is what syntax im going to be using for them which would also affect how easy it would be to add some kind of support for user extended types, with that said, i do think that tuples would cause more trouble than enums to some extend...

Regarding BinInts, it would be a good idea to support them as well, i always forget they exist and now that you talked about it i might add it to the backlog for 0.12 or 0.13.