Addcase cannot be called with two reducers for the same action type

The error message “addcase cannot be called with two reducers for the same action type” indicates that you are trying to assign multiple reducers to handle the same action type when using Redux.

Redux follows the principle of having a single reducer function that handles all actions in a predictable manner. When an action is dispatched, Redux needs to determine which reducer should handle that action based on its action type.

Here’s an example to illustrate the issue:

// Redux code
const reducer1 = (state, action) => {
  switch (action.type) {
    case "ADD_CASE":
      // handle add case action for reducer1
      break;
    default:
      return state;
  }
};

const reducer2 = (state, action) => {
  switch (action.type) {
    case "ADD_CASE":
      // handle add case action for reducer2
      break;
    default:
      return state;
  }
};

// Combine reducers
const rootReducer = combineReducers({
  reducer1,
  reducer2,
});

// Redux store
const store = createStore(rootReducer);
  

In the above example, both reducer1 and reducer2 are handling the same action type "ADD_CASE". This is not allowed in Redux and will result in the error you mentioned.

To solve this issue, you need to refactor your reducers and ensure that each action type is handled by only one reducer. If you have shared logic between reducers, you can extract that logic into separate functions or helper files and use them inside the reducers.

// Updated Redux code
const sharedAddCaseLogic = (state /*, other parameters */) => {
  // shared logic for handling add case action
};

const reducer1 = (state, action) => {
  switch (action.type) {
    case "ADD_CASE":
      // handle add case action for reducer1 using shared logic
      state = sharedAddCaseLogic(state /*, other parameters */);
      break;
    default:
      return state;
  }
};

const reducer2 = (state, action) => {
  switch (action.type) {
    case "ADD_CASE":
      // handle add case action for reducer2 using shared logic
      state = sharedAddCaseLogic(state /*, other parameters */);
      break;
    default:
      return state;
  }
};

// Combine reducers
const rootReducer = combineReducers({
  reducer1,
  reducer2,
});

// Redux store
const store = createStore(rootReducer);
  

By extracting the shared logic into a separate function, you can avoid having multiple reducers handling the same action type. The shared logic function can accept the necessary parameters and modify the state accordingly.