`FormField` causes infinite update loop when given non-primitive `defaultValue` about admin-on-rest

[hon2a]

Reward for tracing it to the source was at least finding a work-around, which is to pass in a constant.

const defaultValue = []
const form = () => (
  <SimpleForm>
    <SelectArrayInput defaultValue={defaultValue} />
  </SimpleForm>
)

[fzaninotto]

That's a common React gotcha: you're passing a new empty array object each time the form rerenders, and specifying a default value rerenders the form. You have to define the default value as a constant (as we've explained for the validators, too).

[hon2a]

I'm aware the code is creating a new Array instance on each render. The fact that it creates infinite update loop is clearly not a "React gotcha", but a bug in how defaultValue is being handled - re-rendering the whole form on defaultValue change has nothing to do with React, it's your choice and it's not obvious in the least. (And if I needed the defaultValue to actually change, I'd have to do some shenanigans like keeping it in an instance property to work around this behaviour.)

I'd say this warrants a clear warning in the docs at the very least. Additionally, the setup seemed to work not too far back, so maybe this changed with some dependency update.

Even more interesting (but unrelated) is how a function in defaultValue is handled. Accepting a function without arguments only makes sense if it's not expected to be pure. Then resolving it only when the function changes doesn't seem to make much sense.

[hon2a]

Btw. the docs actually contain code samples with the same issue (see defaultValue={new Date()} and defaultValue={() => uuid()}), which illustrates my point pretty well.

[fzaninotto]

We're relying on redux-form for handling default values. I believe the problem lies there.

[hon2a]

Nope, you're in control of dispatching its INITIALIZE action. redux-form only reacts by updating the form but doesn't control how this affects the place where you dispatch the action from. (It has no insight into the structure of the app using it.)