Sequelize TypeError: Cannot read properties of undefined (reading 'split')

Question

I am trying to update a sequelize model partially that contains a string array value separated by semicolons.

languages: {
      type: Sequelize.STRING,
      allowNull: false,
      get() {
        if (this.getDataValue('languages') === null) {
          return [];
        } else {
          return this.getDataValue('languages').split(';');
        }
      },
      set(val) {
        if (val.length === 0) {
          this.setDataValue('languages', null);
        } else {
          this.setDataValue('languages', val.join(';'));
        }
      },
    },

Answer 1

I found a solution. Before updating the value it reads the current value and it gives as undefined when it is null in the database. By enhancing the if check it resolves the issue.

 languages: {
  type: Sequelize.STRING,
  allowNull: false,
  get() {
    if (this.getDataValue('languages') === null || this.getDataValue('languages') === undefined) {
      return [];
    } else {
      return this.getDataValue('languages').split(';');
    }
  },
  set(val) {
    if (val.length === 0) {
      this.setDataValue('languages', null);
    } else {
      this.setDataValue('languages', val.join(';'));
    }
  },
},

Answer 2

Short answer

It is better to check if the variable is null or undefined , remember that both values are different. null means nothing, null was assigned, whereas undefined means a variable was declared but no value was assigned to it.

You could do that

 if (!!this.getDataValue('languages')) {
      return this.getDataValue('languages').split(';');
    } else {
      return [];
    }

Long answer

If you want to intercept all your request and replace values, Eg: In case it is a nullable list, I want to display [] , In case it is a nullable boolean, I want to display false .

You may want to use a middleware to do that.

It would be something like below code:

const app = express();

app.set("json replacer", (k, v) => {
  return formatJSONNull(k, v);
});

var formatJSONNull = function (k, v) {
  if (v === null || v === undefined) {
    if (listValues.indexOf(k) >= 0) {
      return [];
    } else if (integerValues.indexOf(k) >= 0) {
      return 0;
    } else if (boolValues.indexOf(k) >= 0) {
      return false;
    } else {
      return "";
    }
  }
  return v;
};

const listValues = ['languages'];

const boolValues = ['language_count'];

const integerValues = ['language_count'];