validations

Crate validations provides an interface to check the validity of arbitrary types.

• validations on crates.io
• Documentation for the latest crates.io release

Overview

The Validate trait provides the validate method, which runs arbitrary validation logic and returns a result indicating whether or not the value is valid. A return value of Ok(()) indicates a valid value. A return value of Err(Errors) indicates an invalid value, and includes details of why the value failed validation.

Errors is a container that can hold both general and field-specific validation errors for an invalid value. An individual validation error is represented by Error, which contains a human-readable error message, and an optional type of the programmer's choice that includes additional contextual information about the error.

Types that implement Validate should handle validation logic for each of their fields, as necessary. If the type of a field implements Validate itself, it's also possible to delegate to the field to validate itself and assign any resulting errors back to the parent type's errors.

Instead of implementing Validate, another approach is to implement validation logic inside the constructor function of a type T, and return Result<T, Errors>, preventing an invalid value from being created in the first place. This may not always be possible, as the value may be created through other means. For example, the value may be deserialized from a format like JSON from an external source. In this case, the Validate trait allows deserialization logic to be decoupled from domain-level validation logic.

Examples

Validating a value:

let entry = AddressBookEntry {
    cell_number: None,
    email: Some(Email("rcohle@dps.la.gov")),
    home_number: Some(PhoneNumber {
        area_code: "555",
        number: "555-5555",
    }),
    name: "Rust Cohle",
};

assert!(entry.validate().is_ok());

Validating a value with a non-field-specific error:

let entry = AddressBookEntry {
    cell_number: None,
    email: Some(Email("rcohle@dps.la.gov")),
    home_number: None,
    name: "Rust Cohle",
};

let errors = entry.validate().err().unwrap();

assert_eq!(
    errors.base().unwrap()[0].message(),
    "at least one phone number is required".to_string()
);

Validating a value with a field error:

let entry = AddressBookEntry {
    cell_number: None,
    email: Some(Email("rcohle@dps.la.gov")),
    home_number: Some(PhoneNumber {
        area_code: "555",
        number: "555-5555",
    }),
    name: "",
};

let errors = entry.validate().err().unwrap();

assert_eq!(
    errors.field("name").unwrap().base().unwrap()[0].message(),
    "can't be blank".to_string()
);

License

MIT