Generated xxxPrimitives query fragments are not immutable

[godness84]

For each model a xxxPrimitives instance is generated in order to quickly select all the simple fields of a model. It's an instance of QueryBuilder, so you can keep calling its methods to append other complex fields.

Obviously (but it was not so obvious for me at first) if you call methods on your xxxPrimitives instance, whenever you use the same xxxPrimitives instance in other parts of your code then you are going to use the mutated instance, not the original one with just the simple fields.

But in many cases it's very handy to describe the fields that you want as "all the primitive fields plus...". Moreover if you add new fields to your graphql schema and run then generator then your xxxPrimitives instance already catches the fields that you've just added.

I think there are 3 ways of solving this:

1. xxxPrimitives instance should be an immutable one. All of its methods should return a new instance.
2. xxxPrimitives should be a factory function that creates a new QueryBuilder every time.
3. an easy way of cloning a QueryBuilder.

Let's take the 3-twitter-clone example. We have:

export function selectFromMessage() {
  return new MessageModelSelector()
}
export const messageModelPrimitives = selectFromMessage().timestamp.text

In order to clone messageModelPrimitives I think we should write

const clonedMessageModelPrimitives = selectFromMessage()._(messageModelPrimitives.toString())

It's not that beautiful and moreover I should do it for each and every model I have.

I propose solution number 2.
To make it backward compatible, we can name it differently. Taking the example above it would be:

export function createMessageModelPrimitives() {
  return selectFromMessage().timestamp.text
}

Is there a meaning in what I say, or am I completely wrong?

[chrisdrackett]

I haven't run into his myself, but your description makes sense. I would agree that solution 2 is the most desirable way forward with this.

[Aryk]

I've ran into this quite a few times.. I figured out to use:

const clonedMessageModelPrimitives = selectFromMessage()._(messageModelPrimitives.toString())

but yeah...it's super ugly...so a few thoughts from me:

1. Why aren't they just generated like functions rs =>rs.id.field and that's the one and only way to do things instead of having multiple different approaches? So if you want to chain, you just wrap the functions (just like you would components). It works well with typescript and with the react way of things.

2. Results selector should take out dups automatically if you combine them...I don't think that happens currently...

3. primitives should include the id (identifier) field IMO. It's a cheap field and basically always needed so that it gets added to mobx tree correctly. This goes along with Allow configuration options for MSTGQL #242 which would allow people to change a regexp and other options for the default selector that gets made.