Crate model_mapper

Expand description

§Model Mapper

A powerful Rust macro to generate boilerplate-free declarations of From, Into, TryFrom, and TryInto traits for converting between structs and enums.

It is designed to handle common patterns like detailed DTOs to internal entities, handling optional fields, nested collections, and even disparate generic types.

§Features

Zero Boilerplate: Automatically implements From, Into, TryFrom, and TryInto.
Flexible Mapping: Handle renamed fields, skipped fields, and additional fields.
Custom Logic: Inject custom conversion logic for specific fields using functions or expressions.
Generics Support: Seamless mapping between generic types with different parameters.
Multiple Targets: Map a single type to multiple other types with conditional configurations.
Nested Mapping: Built-in support for mapping inner values within Option, iterators, and maps.
no_std compatible: Works in no_std environments (with default features disabled).

§Quick Start

The most common use case is mapping between domain entities and DTOs.

#[derive(Mapper)]
#[mapper(from, ty = Entity)]
pub struct Model {
    id: i64,
    name: String,
}

The macro expansion above would generate something like:

impl From<Entity> for Model {
    fn from(Entity { id, name }: Entity) -> Self {
        Self {
            id: Into::into(id),
            name: Into::into(name),
        }
    }
}

Because types doesn’t always fit like a glove, you can provide additional fields on runtime, at the cost of not being able to use the From trait:

pub mod service {
    pub struct UpdateUserInput {
        pub user_id: i64,
        pub name: Option<String>,
        pub surname: Option<String>,
    }
}

#[derive(Mapper)]
#[mapper(
    into(custom = "into_update_user"),
    ty = service::UpdateUserInput,
    add(field = user_id, ty = i64),
    add(field = surname, default(value = None))
)]
pub struct UpdateProfileRequest {
    pub name: String,
}

Would generate something like:

impl UpdateProfileRequest {
    /// Builds a new [service::UpdateUserInput] from a [UpdateProfileRequest]
    pub fn into_update_user(self, user_id: i64) -> service::UpdateUserInput {
        let UpdateProfileRequest { name } = self;
        service::UpdateUserInput {
            user_id,
            surname: None,
            name: Into::into(name),
        }
    }
}

Other advanced use cases are available on the examples folder.

§Detailed Usage

A mapper attribute is required at type-level and it’s optional at field or variant level.

The following attributes are available.

Type level attributes:
- ty = PathType (mandatory): The other type to derive the conversion
- from (optional): Whether to derive From the other type for self
  - custom (optional): Derive a custom function instead of the trait
  - custom = from_other (optional): Derive a custom function instead of the trait, with the given name
- into (optional): Whether to derive From self for the other type
  - custom (optional): Derive a custom function instead of the trait
  - custom = from_other (optional): Derive a custom function instead of the trait, with the given name
- try_from (optional): Whether to derive TryFrom the other type for self
  - custom (optional): Derive a custom function instead of the trait
  - custom = from_other (optional): Derive a custom function instead of the trait, with the given name
- try_into (optional): Whether to derive TryFrom self for the other type
  - custom (optional): Derive a custom function instead of the trait
  - custom = from_other (optional): Derive a custom function instead of the trait, with the given name
- add (optional, multiple): Additional fields (for structs with named fields) or variants (for enums) the other type has and this one doesn’t ¹
  - field = other_field (mandatory): The field or variant name
  - ty = bool (optional): The field type, mandatory for into and try_into if no default value is provided
  - default (optional): The field or variant will be populated using Default::default() (mandatory for enums, with or without value)
    - value = true (optional): The field or variant will be populated with the given expression instead
- ignore_extra (optional): Whether to ignore all extra fields (for structs) or variants (for enums) of the other type ²
Variant level attributes:
- rename = OtherVariant (optional): To rename this variant on the other enum
- add (optional, multiple): Additional fields of the variant that the other type variant has and this one doesn’t ¹
  - field = other_field (mandatory): The field name
  - ty = bool (optional): The field type, mandatory for into and try_into if no default value is provided
  - default (optional): The field or variant will be populated using Default::default()
    - value = true (optional): The field or variant will be populated with the given expression instead
- skip (optional): Whether to skip this variant because the other enum doesn’t have it
  - default (mandatory): The field or variant will be populated using Default::default()
    - value = get_default_value() (optional): The field or variant will be populated with the given expression instead
- ignore_extra (optional): Whether to ignore all extra fields of the other variant (only valid for from and try_from) ²
Field level attributes:
- rename = other_name (optional): To rename this field on the other type
- skip (optional): Whether to skip this field because the other type doesn’t have it
  - default (optional): The field or variant will be populated using Default::default()
    - value = get_default_value() (optional): The field or variant will be populated with the given expression instead
- with = mod::my_function (optional): If the field type doesn’t implement Into or TryInto the other, this property allows you to customize the behavior by providing a conversion function
- into_with = mod::my_function (optional): The same as above but only for the into or try_into derives
- from_with = mod::my_function (optional): The same as above but only for the from or try_from derives
Additional hints on how to map fields:
- opt (optional): The field is an Option and the inner value shall be mapped ³
- iter (optional): The field is an iterator and the inner value shall be mapped ³
- map (optional): The field is a hashmap-like iterator and the inner value shall be mapped ³
- with = mod::my_function (optional): If the field type doesn’t implement Into or TryInto the other, this property allows you to customize the behavior by providing a conversion function
- from_with = mod::my_function (optional): The same as above but only for the from or try_from derives
- from_with = mod::my_function (optional): The same as above but only for the from or try_from derives

¹ When providing additional fields without defaults, the From and TryFrom traits can’t be derived and a custom function will be required instead. When deriving into or try_into, the ty must be provided as well.

² When ignoring fields or variants it might be required that the enum or the struct implements Default in order to properly populate it.

³ Hints can be nested, for example: opt(vec), vec(opt(with = "my_custom_fn"))

§Multiple derives

When deriving conversions for a single type, attributes can be set directly:

#[mapper(from, into, ty = OtherType, add(field = field_1, default), add(field = field_2, default))]
struct MyStruct;

But we can also derive conversions for multiple types by wrapping the properties on a derive attribute:

#[mapper(derive(try_into, ty = OtherType, add(field = field_1, default)))]
#[mapper(derive(from, ty = YetAnotherType))]
struct MyStruct;

If multiple conversions are involved, both variant and field level attributes can also be wrapped in a when attribute and must set the ty they refer to:

#[mapper(when(ty = OtherType, with = ToString::to_string))]
#[mapper(when(ty = YetAnotherType, skip(default)))]
struct MyStruct;