Conditional Schemas

Angular Signal Forms already provide a declarative way to apply schemas conditionally with applyWhen.

applyWhen(
  path.billingAddress,
  (ctx) => ctx.valueOf(path.useDifferentBillingAddress),
  AddressSchema
);

This works well for simple “apply this schema when…” cases.

However, many forms also need an explicit fallback state.

For example, when a billing address is not used, the section should not only stop applying AddressSchema. It may also need to become disabled, hidden, reset, or replaced by another schema.

With Angular Signal Forms this usually requires a second condition with manual negation:

applyWhen(
  path.billingAddress,
  (ctx) => ctx.valueOf(path.useDifferentBillingAddress),
  AddressSchema
);

applyWhen(
  path.billingAddress,
  (ctx) => !ctx.valueOf(path.useDifferentBillingAddress),
  InactiveBillingAddressSchema
);

applyIf makes this branching explicit:

applyIf(
  path.billingAddress,
  valueEquals(path.useDifferentBillingAddress, true),
  AddressSchema,
  InactiveBillingAddressSchema
);

This is the main difference:

applyWhen = apply schema when a condition is true

applyIf = apply one schema when true, another schema when false

So applyIf is not a replacement for applyWhen.

It is useful when a conditional form section has two meaningful states.