async-graphql/docs/en/src/default_value.md

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# Default value
You can define default values for input value types.
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Below are some examples.
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## Object field
```rust
# extern crate async_graphql;
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use async_graphql::*;
struct Query;
fn my_default() -> i32 {
30
}
#[Object]
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impl Query {
// The default value of the value parameter is 0, it will call i32::default()
async fn test1(&self, #[graphql(default)] value: i32) -> i32 { todo!() }
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// The default value of the value parameter is 10
async fn test2(&self, #[graphql(default = 10)] value: i32) -> i32 { todo!() }
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// The default value of the value parameter uses the return result of the my_default function, the value is 30.
async fn test3(&self, #[graphql(default_with = "my_default()")] value: i32) -> i32 { todo!() }
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}
```
## Interface field
```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!() }
# }
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use async_graphql::*;
#[derive(Interface)]
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#[graphql(
field(name = "test1", type = "i32", arg(name = "value", type = "i32", default)),
field(name = "test2", type = "i32", arg(name = "value", type = "i32", default = 10)),
field(name = "test3", type = "i32", arg(name = "value", type = "i32", default_with = "my_default()")),
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)]
enum MyInterface {
MyObj(MyObj),
}
```
## Input object field
```rust
# extern crate async_graphql;
# fn my_default() -> i32 { 5 }
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use async_graphql::*;
#[derive(InputObject)]
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struct MyInputObject {
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#[graphql(default)]
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value1: i32,
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#[graphql(default = 10)]
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value2: i32,
#[graphql(default_with = "my_default()")]
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value3: i32,
}
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```