`useLiveQuery` needs a default value.

[thruflo]

Currently, useLiveQuery returns undefined until the initial query has returned. This leads to a bunch of if results !=== undefined checks in your component code.

For example:

function Component() {
  const results = useLiveQuery(`
    SELECT * FROM items
      WHERE foo = $1
  `, ['bar'])
  const items = results !== undefined ? results.rows : []
  // ...

Now, if you look at useState, it avoids this by supporting a default value:

function Component() {
  const [results, setResults] = useState([])
  // ...

I propose the ergonomic improvement of supporting a default value with useLiveQuery:

function Component() {
  const { rows: items } = useLiveQuery(`
    SELECT * FROM items
      WHERE foo = $1
  `, ['bar'], [])
  // ...

Using a third positional argument for it is slightly tricky with query parameters (hence cherry picking an example of a query that uses parameters), because then you need to specify the query parameters arg even if not using them. I guess an alternative would be a {default: value} option (more explicit but also more verbose).

[tdrz]

an alternative would be a {default: value} option (more explicit but also more verbose).

I think it's ok to be more verbose when you need that option. If we default to [] I guess would be fine for most users.

[thruflo]

I think any default value should be explicit. It's useful, when you want to, to be able to distinguish between empty results and no results yet.

[tdrz]

const items = results !== undefined ? results.rows : []

const items = results?.rows ?? []

[samwillis]

The live.query() api excepts both optional arguments of a single options object arguments:

https://github.com/electric-sql/pglite/blob/0c7454d1cef9725c6dc3f1e26352016c6145c3be/packages/pglite/src/live/interface.ts#L29-L51

useLiveQuery also has multiple call signatures:

https://github.com/electric-sql/pglite/blob/0c7454d1cef9725c6dc3f1e26352016c6145c3be/packages/pglite-react/src/hooks.ts#L101-L112

although not a option arg one. Maybe we should add that.