i am new to redux and react i am trying to update the nested state in REDUX store, but unable to sort it out

Question

where am i missing? please help in sorting this out _/_ i have trouble in updating the redux store state correctly without breaking

This is my current state in redux store state before posting the data

next state Object {
  "highlights": Object {
    "errMess": null,
    "highlights": Array [],
    "isLoading": true,
  },
  "posts": Object {
    "errMess": null,
    "isLoading": false,
    "posts": Array [
      Object {
        "__v": 0,
        "_id": "5f37c3ebc8cb6a46c89bc33c",
        "by": Object {
          "_id": "5ed8d7fcfd3da42bc426992a",
          "name": "mad",
          "username": "mad",
        },
        "content": "this is first post",
        "contentWarn": false,
        "createdAt": "2020-08-15T11:15:55.986Z",
        "flaged": false,
        "heading": "first pot",
        "report": 0,
        "updatedAt": "2020-08-15T11:15:55.986Z",
      },
    ],
  },
}

then add new post action is performed using reducer====>

export const posts = (
  state = { isLoading: true, errMess: null, posts: [] },
  action
) => {
  switch (action.type) {
 
   case ActionTypes.UPDATE_POSTS:
      return {
        posts: state.posts.posts.concat(action.payload),
      };
    default:
      return state;
  }
};

this is the error returned

 action     Object {
  "payload": [TypeError: undefined is not an object (evaluating 'state.posts.posts.concat')],
  "type": "UPDATE_POSTS_FAILED",
}

undefined is not an object (evaluating 'state.posts.posts.concat')
* Redux\posts.js:24:13 in posts

this is the result i wanted to happen

next state Object {
  "highlights": Object {
    "errMess": null,
    "highlights": Array [],
    "isLoading": true,
  },
  "posts": Object {
    "errMess": null,
    "isLoading": false,
    "posts": Array [
      Object {
        "__v": 0,
        "_id": "5f37c3ebc8cb6a46c89bc33c",
        "by": Object {
          "_id": "5ed8d7fcfd3da42bc426992a",
          "name": "mad",
          "username": "mad",
        },
        "content": "this is first post",
        "contentWarn": false,
        "createdAt": "2020-08-15T11:15:55.986Z",
        "flaged": false,
        "heading": "first pot",
        "report": 0,
        "updatedAt": "2020-08-15T11:15:55.986Z",
      },
     Object {
        "__v": 0,
        "_id": "5f37c3ebc8cb6a46c89bc33c",
        "by": Object {
          "_id": "5ed8d7fcfd3da42bc426992a",
          "name": "mad",
          "username": "mad",
        },
        "content": "this is second post",
        "contentWarn": false,
        "createdAt": "2020-08-15T11:15:55.986Z",
        "flaged": false,
        "heading": "second post",
        "report": 0,
        "updatedAt": "2020-08-15T11:15:55.986Z",
      }
    ],
  },
}

Answer 1

Your reducer should have this structures with two level posts:

export const posts = (
  state = {
    highlights: {
      errMess: null,
      highlights: [],
      isLoading: true,
    },
    posts: { isLoading: true, errMess: null, posts: [] },
  },
  action
) => {
  switch (action.type) {
    case ActionTypes.UPDATE_POSTS:
      return {
        ...state,
        posts: state.posts.posts.concat(action.payload),
      };
    default:
      return state;
  }
};

and try to keep the same data structure in the state, like highlights !

Answer 2

      return {
        ...state,
        posts: state.posts.concat(action.payload),
      }

this reducer worked Note: I am using highlight reducer in separate file