Dependent Fields

A dependent field is a purely output field whose value changes whenever at least one field it depends on is provided and accepted (e.g. username_last_updated_at should only update whenever username changes).

• It must have either a default static value or a resolver for the default value.
• It must depend on at least one other field - lax, required, virtual, or another dependent field (no circular dependencies). The parent fields are supplied as the second argument to dependent_field.
• It must have a resolver to generate new values whenever a parent field is provided and accepted.
• It may use readonly to stop accepting further updates once its value differs from its default.
• It may have on_delete and on_success event handlers.

Example

value is a lax field with a default of 0. computed is a dependent field that equals value + 1 (with its own fallback default of 1). The dependency on value is declared as the second argument to dependent_field:

use std::{future::ready, sync::LazyLock};
use ivo::{dependent_field, lax_field, IvoContext, IvoInputStruct, IvoModel, IvoStruct};

type Ctx = IvoContext<DataInput, Data>;

#[derive(Clone, Debug, PartialEq, IvoInputStruct)]
struct DataInput {
    pub value: i32,
}

#[derive(Debug, Clone, PartialEq, IvoStruct)]
struct Data {
    pub value: i32,
    pub computed: i32,
}

static MODEL: LazyLock<IvoModel<DataInput, Data>> = LazyLock::new(|| {
    IvoModel::new(
        |f| {
            f.field(lax_field("value").default(0)).field(
                dependent_field("computed", ["value"])
                    .default(1)
                    .resolve(|ctx: Ctx, _| ready(ctx.values().value.unwrap_or(0) + 1)),
            )
        },
        |o| o,
    )
});

Examples

• Default values
• Dependent on dependent
• Readonly

Try it in the browser

value is a lax field with a default of 0. computed is a dependent field that equals value + 1 (with its own fallback default of 1).

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