Function useResolveHaystackValue

A hook to use a value from an haystack-server as react state.

This hook should be used when input flexibility is required. It is meant to abstract how data is actually retrieved/polled/written, enabling at the same time a data driven approach.

It takes a ResolvableDict that contains the record data and a meta tag that indicates how to interact with that record to poll and write an HVal.

See

• ResolvableDict for the options available.

IMPORTANT: this hook requires a ClientContext to work.

• https://github.com/j2inn/haystack-nclient

Example

Here’s a usage example:

const [point] = useReadByFilter('point and temp and zone and sp').grid // One-shot reading the first point that matches the filter

//Adding meta data to the dict (this could be done server side)
const resolvableDict1 = point?.newCopy().set('meta', {resolveType: 'point'}) as Resolvable<HNum>
const resolvableDict2 = point?.newCopy().set('meta', {resolveType: 'tag', readTag: 'precision'}) as Resolvable<HNum>

// The actual state used depends on the metadata in the dict:
const [pointValue, setPointValue, point] = useResolveHaystackValue<HNum>(resolvableDict1)
const [pointPrecision, setPointPrecision, point] = useResolveHaystackValue<HNum>(resolvableDict2)

Returns

a resolved value and a function to update it on the server, if the value is not resolved it is passed through.