# 默认值
你可以为输入值类型定义默认值,下面展示了在不同类型上默认值的定义方法。
## 对象字段参数
```rust
# extern crate async_graphql;
use async_graphql::*;
struct Query;
fn my_default() -> i32 {
30
}
#[Object]
impl Query {
// value 参数的默认值为 0,它会调用 i32::default()
async fn test1(&self, #[graphql(default)] value: i32) -> i32 { todo!() }
// value 参数的默认值为 10
async fn test2(&self, #[graphql(default = 10)] value: i32) -> i32 { todo!() }
// value 参数的默认值使用 my_default 函数的返回结果,值为 30
async fn test3(&self, #[graphql(default_with = "my_default()")] value: i32) -> i32 { todo!() }
}
```
## 接口字段参数
```rust
# extern crate async_graphql;
# fn my_default() -> i32 { 5 }
# struct MyObj;
# #[Object]
# impl MyObj {
# async fn test1(&self, value: i32) -> i32 { todo!() }
# async fn test2(&self, value: i32) -> i32 { todo!() }
# async fn test3(&self, value: i32) -> i32 { todo!() }
# }
use async_graphql::*;
#[derive(Interface)]
#[graphql(
field(name = "test1", ty = "i32", arg(name = "value", ty = "i32", default)),
field(name = "test2", ty = "i32", arg(name = "value", ty = "i32", default = 10)),
field(name = "test3", ty = "i32", arg(name = "value", ty = "i32", default_with = "my_default()")),
)]
enum MyInterface {
MyObj(MyObj),
}
```
## 输入对象 (InputObject)
```rust
# extern crate async_graphql;
# fn my_default() -> i32 { 5 }
use async_graphql::*;
#[derive(InputObject)]
struct MyInputObject {
#[graphql(default)]
value1: i32,
#[graphql(default = 10)]
value2: i32,
#[graphql(default_with = "my_default()")]
value3: i32,
}
```