Detect session.validators for derive extraction (#1562)

* Detect session.validators for derive extraction

* Add comment

* Indexed extraction without session

packages/api-derive/src/session/indexes.ts

@@ -6,19 +6,24 @@ import { ApiInterfaceRx } from '@polkadot/api/types';
 import { EraIndex, SessionIndex } from '@polkadot/types/interfaces';
 import { DeriveSessionIndexes } from '../types';
 
-import { Observable } from 'rxjs';
+import { Observable, of } from 'rxjs';
 import { map } from 'rxjs/operators';
-import { u32 } from '@polkadot/types';
+import { createType, u32 as U32 } from '@polkadot/types';
 
 import { drr } from '../util';
 
 export function indexes (api: ApiInterfaceRx): () => Observable<DeriveSessionIndexes> {
   return (): Observable<DeriveSessionIndexes> =>
-    api.queryMulti<[SessionIndex, EraIndex, u32]>([
-      api.query.session.currentIndex,
-      api.query.staking.currentEra,
-      api.query.staking.validatorCount
-    ]).pipe(
+    (
+      // Some chains (eg. very limited node-template), does not have session
+      api.query.session && api.query.staking
+        ? api.queryMulti<[SessionIndex, EraIndex, U32]>([
+          api.query.session.currentIndex,
+          api.query.staking.currentEra,
+          api.query.staking.validatorCount
+        ])
+        : of([createType('SessionIndex', 1), createType('EraIndex', 1), new U32()])
+    ).pipe(
       map(([currentIndex, currentEra, validatorCount]): DeriveSessionIndexes => ({
         currentIndex, currentEra, validatorCount
       })),

packages/api-derive/src/staking/overview.ts

@@ -25,7 +25,7 @@ export function overview (api: ApiInterfaceRx): () => Observable<DerivedStakingO
         combineLatest([
           of({ currentElected, currentEra, currentIndex, validators, validatorCount }),
           // this will change on a per block basis, keep it innermost (and it needs eraIndex)
-          api.query.staking.currentEraPointsEarned
+          api.query.staking?.currentEraPointsEarned
             ? api.query.staking.currentEraPointsEarned<EraPoints>(currentEra)
             : of(createType('EraPoints'))
         ])

packages/api-derive/src/staking/validators.ts

@@ -6,7 +6,7 @@ import { AccountId } from '@polkadot/types/interfaces';
 import { ApiInterfaceRx } from '@polkadot/api/types';
 import { DeriveStakingValidators } from '../types';
 
-import { Observable } from 'rxjs';
+import { Observable, of } from 'rxjs';
 import { map } from 'rxjs/operators';
 import { Vec } from '@polkadot/types';
 
@@ -17,10 +17,16 @@ import { drr } from '../util';
  */
 export function validators (api: ApiInterfaceRx): () => Observable<DeriveStakingValidators> {
   return (): Observable<DeriveStakingValidators> =>
-    api.queryMulti<[Vec<AccountId>, Vec<AccountId>]>([
-      api.query.session.validators,
-      api.query.staking.currentElected
-    ]).pipe(
+    (
+      // Sadly the node-template is (for some obscure reason) not comprehensive, so while the derive works
+      // in all actual real-world deployed chains, it does create some confusion for limited template chains
+      api.query.session && api.query.staking
+        ? api.queryMulti<[Vec<AccountId>, Vec<AccountId>]>([
+          api.query.session.validators,
+          api.query.staking.currentElected
+        ])
+        : of([[], []] as [AccountId[], AccountId[]])
+    ).pipe(
       map(([validators, currentElected]): DeriveStakingValidators => ({
         currentElected, validators
       })),