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I am trying to select an object by Id from the entity state. Below is my reducer.

 export interface MessageState extends EntityState<Message> 
 // additional entities state properties
 loaded: boolean;
 loading: boolean;


export const adapter: EntityAdapter<Message> = createEntityAdapter<Message>(
 selectId: (msg: Message) => msg.messageId,
);

export const initialState: MessageState = adapter.getInitialState(
 // additional entity state properties
 loaded: false,
 loading: false,
);

export function reducer(state = initialState, action: MessageActionsUnion): MessageState 
 switch (action.type) 

 case MessageActionTypes.UPSERT_Message: 
 return ...state, loading: true, loaded: false ;
 

 case MessageActionTypes.UPSERT_Message_SUCCESS: 
 return adapter.upsertOne(action.payload.Message,
 
 ...state, loaded: true, loading: false,
 );

 

 default: 
 return state;
 
 

Below is my index.ts file

export interface State extends fromRoot.AppState 
 queueModule: QueueState;


export interface QueueState 
 msgHeaders: fromMsgHeaders.MessageHeaderState


export const reducers: ActionReducerMap<QueueState> = 
 msgHeaders: fromMsgHeaders.reducer

;

export const getQueueState$ = createFeatureSelector<QueueState>('queueModule');

I am trying to form a selector when passed an Id will return the value from the entity.

 export const selectMessages = createSelector(
 fromFeatures.getQueueState$,
 (state: fromFeatures.QueueState) => state.msgs
 );

 export const 
 selectAll: selectAllMessages,
 selectEntities: selectMessagesEntities,
 selectIds: selectMessagesIds,
 selectTotal: selectMessagesTotal
 = adapter.getSelectors(selectMessages);

I looked at many resources, but none are clear on how to select an object by passing the id.

@ngrx/entity doesn't provide a getOneById selector.

In most of the cases, this is something you shouldn't have to do.

That being said there are ways of creating a selector which does exactly this, for more info see (NgRx: Parameterized selectors)[https://blog.angularindepth.com/ngrx-parameterized-selector-e3f610529f8].

For example:

export const getCount = createSelector(
 getCounterValue, 
 (counter, props) => counter * props.multiply
);

export const selectCustomer = (id: string) => createSelector(
 selectCustomers,
 customers => customers[id]
);

@ngrx/entity does provide a getEntityValueById after their release of v6.1.0 (ngrx entity changelog) where they have introduced dictionary.

Thus using this, I was able to pull a single value of an entity by its id in the below way.

// in the selector
import Dictionary from '@ngrx/entity;

export const getMessageById = () => 
 return createSelector(
 selectMessagesEntities, 
 (entities: Dictionary<Message>, props: messageId: number ) => 
 return entities[props.messageId];
 ,
 );
;


//to call the selector


this.msg$ = this.store.pipe(select(
 fromStore.getMessageById(), messageId: 10 
 )).pipe(
 map(
 (message: Message) => 
 return this.msg = message;
 ,
 )
 );

Also a great reference for this approach has been documented
here.