added initial internal overview.mdx

Author: riqts

docs/rtk-query/internal/overview.mdx

@@ -0,0 +1,61 @@
+# RTKQ internal
+
+## Overview
+When `createApi()` is called it takes the options provided and calls internally the `buildCreateApi()` function passing into it two modules:
+
+*Modules are RTK-Query's method of customizing how the `createApi` method handles endpoints.*
+
+- `coreModule()` - responsible for the majority of the internal handling using core redux logic i.e. slices, reducers, asyncThunks.
+- `reactHooksModule()` - a module that generates react hooks from endpoints using react-redux
+
+## Core Module
+
+The core module takes the `api` and the options passed to `createApi()`. In turn an internal set of "build" methods are called. Each of these build methods create a set of functions which are assigned to either `api.util` or `api.internalActions` and/or passed to a future "build" step.
+
+### buildThunks
+RTK-Query's internal functionality operates using the same `asyncThunk` exposed from RTK. In the first "build" method, a number of thunks are generated for the core module to use:
+
+- `queryThunk`
+- `mutationThunk`
+- `patchedQueryData`
+- `updateQueryData`
+- `upsertQueryData`
+- `prefetch`
+- `buildMatchThunkActions`
+
+### buildSlice
+RTK-Query uses a very familiar redux-centric architecture. Where the `api` is a slice of your store, the `api` has its own slices created within it. These slices are where the majority of the RTKQ magic happens.
+
+The slices built inside this "build" are:
+*Some of which have their own actions*
+- querySlice
+- mutationSlice
+- invalidationSlice
+- subscriptionSlice (used as a dummy slice to generate actions internally)
+- internalSubscriptionsSlice
+- configSlice (internal tracking of focus state, online state, hydration etc)
+
+buildSlice also exposes the core action `resetApiState` which is subsequently added to the `api.util`
+
+### buildMiddleware
+RTK-Query has a series of custom middlewares established within its store to handle additional responses in addition to the core logic established within the slices from buildSlice.
+
+Each middleware built during this step is referred to internally as a "Handler" and are as follows:
+
+- `buildDevCheckHandler
+- `buildCacheCollectionHandler
+- `buildInvalidationByTagsHandler
+- `buildPollingHandler
+- `buildCacheLifecycleHandler
+- `buildQueryLifecycleHandler
+
+### buildSelectors
+build selectors is a crucial step that exposes to the `api` and utils:
+
+- `buildQuerySelector
+- `buildMutationSelector
+- `selectInvalidatedBy
+- `selectCachedArgsForQuery
+
+### return
+Finally each endpoint passed into the `createApi()` is iterated over and assigned either the query or the mutation selectors, initiators and match cases.

website/sidebars.json

@@ -149,6 +149,7 @@
           "label": "Internal Docs",
           "collapsed": true,
           "items": [
+            "rtk-query/internal/overview",
             "rtk-query/internal/queryThunk",
             {
               "type": "category",