Realm Object Field Using Default Value Based on Another Field

When working with TypeScript and Realm, you may come across a scenario where you need to set a default value for a field in a Realm object based on the value of another field. In this blog post, we will explore different solutions to achieve this.

Solution 1: Using a Getter Function

One way to set a default value based on another field is by using a getter function in your Realm object. This function will be called whenever the field is accessed, allowing you to dynamically set the default value based on the value of another field.

  import Realm from 'realm';

  class MyObject extends Realm.Object {
    get defaultValueBasedOnAnotherField() {
      if (!this.anotherField) {
        return 'default value';
      }
      // Calculate and return the default value based on anotherField
      return `default value based on ${this.anotherField}`;
    }
  }

  const schema = {
    name: 'MyObject',
    properties: {
      anotherField: 'string',
      defaultValueBasedOnAnotherField: 'string',
    },
  };

  const realm = new Realm({ schema: [schema] });
  

In the above code snippet, we define a getter function defaultValueBasedOnAnotherField in the MyObject class. This function checks if the anotherField is empty and returns a default value if it is. Otherwise, it calculates and returns the default value based on the value of anotherField.

Solution 2: Using a Pre-Save Hook

Another approach is to use a pre-save hook in Realm. This hook will be triggered before saving the object to the database, allowing you to set the default value based on another field.

  import Realm from 'realm';

  class MyObject extends Realm.Object {}

  MyObject.schema = {
    name: 'MyObject',
    properties: {
      anotherField: 'string',
      defaultValueBasedOnAnotherField: 'string',
    },
    // Define a pre-save hook
    preSave() {
      if (!this.anotherField) {
        this.defaultValueBasedOnAnotherField = 'default value';
      } else {
        // Calculate and set the default value based on anotherField
        this.defaultValueBasedOnAnotherField = `default value based on ${this.anotherField}`;
      }
    },
  };

  const realm = new Realm({ schema: [MyObject] });
  

In the above code snippet, we define a pre-save hook using the preSave method in the MyObject class. This hook checks if the anotherField is empty and sets a default value if it is. Otherwise, it calculates and sets the default value based on the value of anotherField.

Conclusion

Setting a default value for a Realm object field based on another field can be achieved using either a getter function or a pre-save hook. Both solutions provide flexibility and allow you to dynamically set the default value based on your specific requirements.

By utilizing these techniques, you can ensure that your Realm objects have default values that are based on the values of other fields, providing a more robust and efficient data model.

Remember to consider the specific needs of your application and choose the solution that best fits your requirements.