createSelector
createSelector
createSelector
The createSelector
utility from the Reselect library, re-exported for ease of use.
For more details on using createSelector
, see:
Note: Prior to v0.7, RTK re-exported
createSelector
fromselectorator
, which allowed using string keypaths as input selectors. This was removed, as it ultimately did not provide enough benefits, and the string keypaths made static typing for selectors difficult.
createDraftSafeSelector
createDraftSafeSelector
In general, we recommend against using selectors inside of reducers:
Selectors typically expect the entire Redux state object as an argument, while slice reducers only have access to a specific subset of the entire Redux state
Reselect's
createSelector
relies on reference comparisons to determine if inputs have changed, and if an Immer Proxy-wrapped draft value is passed in to a selector, the selector may see the same reference and think nothing has changed.
However, some users have requested the ability to create selectors that will work correctly inside of Immer-powered reducers. One use case for this might be collecting an ordered set of items when using createEntityAdapter
, such as const orderedTodos = todosSelectors.selectAll(todosState)
, and then using orderedTodos
in the rest of the reducer logic.
Besides re-exporting createSelector
, RTK also exports a wrapped version of createSelector
named createDraftSafeSelector
that allows you to create selectors that can safely be used inside of createReducer
and createSlice
reducers with Immer-powered mutable logic. When used with plain state values, the selector will still memoize normally based on the inputs. But, when used with Immer draft values, the selector will err on the side of recalculating the results, just to be safe.
All selectors created by entityAdapter.getSelectors
are "draft safe" selectors by default.
Example:
After executing that, unsafe1
and unsafe2
will be of the same value, because the memoized selector was executed on the same object - but safe2
will actually be different from safe1
(with the updated value of 2
), because the safe selector detected that it was executed on a Immer draft object and recalculated using the current value instead of returning a cached value.
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