How to alter keys in immutable map? - immutable.js

Question

I've a data structure like this (generated by normalizr):
const data = fromJS({
templates: {
"83E51B08-5F55-4FA2-A2A0-99744AE7AAD3":
{"uuid": "83E51B08-5F55-4FA2-A2A0-99744AE7AAD3", test: "bla"},
"F16FB07B-EF7C-440C-9C21-F331FCA93439":
{"uuid": "F16FB07B-EF7C-440C-9C21-F331FCA93439", test: "bla"}
}
})
Now I try to figure out how to replace the UUIDs in both the key and the value of the template entries. Basically how can I archive the following output:
const data = fromJS({
templates: {
"DBB0B4B0-565A-4066-88D3-3284803E0FD2":
{"uuid": "DBB0B4B0-565A-4066-88D3-3284803E0FD2", test: "bla"},
"D44FA349-048E-4006-A545-DBF49B1FA5AF":
{"uuid": "D44FA349-048E-4006-A545-DBF49B1FA5AF", test: "bla"}
}
})
A good candidate seems to me the .mapEntries() method, but I'm struggling on how to use it ...
// this don't work ... :-(
const result = data.mapEntries((k, v) => {
const newUUID = uuid.v4()
return (newUUID, v.set('uuid', newUUID))
})
Maybe someone can give me a hand here?

Answer 1

mapEntries is the correct method. From the documentation, the mapping function has the following signature:
mapper: (entry: [K, V], index: number, iter: this) => [KM, VM]
This means that the first argument is the entry passed in as an array of [key, value]. Similarly, the return value of the mapper function should be an array of the new key and the new value. So your mapper function needs to look like this:
([k, v]) => {
const newUUID = uuid.v4()
return [newUUID, v.set('uuid', newUUID)]
}
This is equivalent to the following (more explicit) function:
(entry) => {
const key = entry[0]; // note that key isn't actually used, so this isn't necessary
const value = entry[1];
const newUUID = uuid.v4()
return [newUUID, value.set('uuid', newUUID)]
}
One thing to note is that the templates are nested under the templates property, so you can't map data directly -- instead you'll want to use the update function.
data.update('templates', templates => template.mapEntries(...)))
So putting everything together, your solution should look like the following:
const result = data.update('templates', templates =>
templates.mapEntries(([k, v]) => {
const newUUID = uuid.v4()
return [newUUID, v.set('uuid', newUUID)]
})
);