Allow specifying required fields on Realm.Object

[tomduncalf]

What, How & Why?

The current types for Realm.Object (post-class based models) make it so that when you construct an object with new MyObject(realm: Realm, objectValues: Record<string, whatever>), you are required to specify a value for every property of the schema in objectValues.

In the case of schemas with default values specified, this means you would need to work around type errors if you do not want to specify an explicit value for the properties with defaults – e.g. you could specify fieldName: undefined which would result in the default being used, which works but is a little clumsy.

This is likely to become a more common use case post-Typescript models, as we are making it very natural to specify schema defaults.

This change makes it so that all fields of the schema are optional, unless explicitly specified as part of a union type for the second type parameter: class MyObject extends Realm.Object<MyObject, 'requiredField1' | 'requiredField2'> – so users should specify any required fields (i.e. ones which do not have a default value) in this type parameter.

If required fields are not specified in the type parameter, TypeScript will treat them as optional, which could lead to errors where required fields are not being passed in. On the other hand, this will not break existing code as we are by default relaxing the strictness of the type.

The reason behind making all fields optional by default rather than required is that core has an internal default value for all types, so this will not lead to runtime errors. It would of course be much nicer to be able to infer which fields have a default value being assigned but I don't think there's any way to express this in TypeScript.

☑️ ToDos

• 📝 Changelog entry
• 📝 Compatibility label is updated or copied from previous entry
• 📝 Update COMPATIBILITY.md
• 🚦 Tests
• 🔀 Executed flexible sync tests locally if modifying flexible sync
• 📦 Updated internal package version in consuming package.jsons (if updating internal packages)
• 📱 Check the React Native/other sample apps work if necessary
• 📝 Public documentation PR created or is not necessary
• 💥 Breaking label has been applied or is not necessary

If this PR adds or changes public API's:

• typescript definitions file is updated
• jsdoc files updated
• Chrome debug API is updated if API is available on React Native