added option to supply a custom from and to json converter function

[Manuelbaun]

What kind of change does this PR introduce?

It adds the option to supply a converter object with a from and to json converter function in the PostgrestBuilder-class.

What is the current behavior?

When fetching from the backend, the data gets parsed as regular JSON. This is fine, if no additionally processing is needed. But in case a replacer is needed in order to convert a ISO DateString to a Date Object. It is very handy to do that in the JSON.parse function call.

What is the new behavior?

With this change it is now possible to supply a convertor object, which is basically just a object with two props: fromJSON, toJSON

Example:

import { parseISO } from 'date-fns';

/// ...
client<MyType>('my_table')
.select('*')
.match({id: '1234'})
.withConverter({fromJSON: (k:string, v:any)=>{
      return ['start', 'end'].includes(k)? parseISO(v): v;
}
/// ...

Additional context

feel free to suggest another name.

[soedirgo]

Any reason this couldn't just be:

import { parseISO } from 'date-fns';

/// ...
client<MyType>('my_table')
.select('*')
.match({id: '1234'})
.then(res => { ...res, data: transformData(data) })
/// ...

?

[Manuelbaun]

When I see it correctly, the then-method of the PostgrestBuilder-class already uses JSON.parse/JSON.stringify. If I do it like you suggested, then data would be already parsed and I had to walk the received object manually.

Lets assume, that is the structure/interface of MyType:

interface MyType {
    name: string;
    start: Date; // from the DB, we receive actually an string
    end: Date; // same here
    // some other important fields
    embeddedResource: {
        start: Date; // same here
        end: Date; // and here
        // some other important fields
        someOtherEmbeddedResource: {
            start: Date; // and here
            end: Date; // and here
            // some other important fields
        }[];
    }[];
}

So when JSON.parse parses the JSON, I could check the keys and convert the DateISO String, which I receive from postgrest, and parse it to date. Therefore I dont have to walk the structure by hand. The replacer does it already. So when I call then( ...., then the data start, end attributes would be parsed as a Date-Object.

[soedirgo]

If you really have to, you can always do:

const transformData = data => data.map(row => JSON.parse(JSON.stringify(row), fromJSON))

I can see the value of using reviver/replacer (e.g. performance in the above case), but I think the use case is not general enough to warrant extending the API.

[Manuelbaun]

Previously I used your posted suggestion, but the performance aspect lead to this pull request. parse -> stringify-> parse doesnt seem right, if it can happen in one go. Besides, the api would be optional.

But I also understand not to easily extending the API. If more from the comunity have use for this pull request, you could revisit it.