# SimpleObject
`SimpleObject` directly maps all the fields of a struct to GraphQL object. You cannot define a resolver function on it - for that, see [Object](define_complex_object.html).
The example below defines an object `MyObject` which includes the fields `a` and `b`. `c` will be not mapped to GraphQL as it is labelled as `#[graphql(skip)]`
```rust
use async_graphql::*;
#[derive(SimpleObject)]
struct MyObject {
/// Value a
a: i32,
/// Value b
b: i32,
#[graphql(skip)]
c: i32,
}
```
## Generic `SimpleObject`s
If you want to reuse an `SimpleObject` for other types, you can define a generic SimpleObject
and specify how its concrete types should be implemented.
In the following example, two `SimpleObject` types are created:
```rust
#[derive(SimpleObject)]
#[graphql(concrete(name = "SomeName", params(SomeType)))]
#[graphql(concrete(name = "SomeOtherName", params(SomeOtherType)))]
pub struct SomeGenericObject<T: OutputType> {
field1: Option<T>,
field2: String
}
```
Note: Each generic parameter must implement `OutputType`, as shown above.
The schema generated is:
```gql
type SomeName {
field1: SomeType
field2: String!
}
type SomeOtherName {
field1: SomeOtherType
field2: String!
}
```
In your resolver method or field of another object, use as a normal generic type:
```rust
#[derive(SimpleObject)]
pub struct YetAnotherObject {
a: SomeGenericObject<SomeType>,
b: SomeGenericObject<SomeOtherType>,
}
```
You can pass multiple generic types to `params()`, separated by a comma.
## Complex resolvers
Sometimes most of the fields of a GraphQL object simply return the value of the structure member, but a few
fields are calculated. Usually we use the `Object` macro to define such a GraphQL object.
But this can be done more beautifully with the `ComplexObject` macro. We can use the `SimpleObject` macro to define
some simple fields, and use the `ComplexObject` macro to define some other fields that need to be calculated.
```rust
#[derive(SimpleObject)]
#[graphql(complex)] // NOTE: If you want the `ComplexObject` macro to take effect, this `complex` attribute is required.
struct MyObj {
a: i32,
b: i32,
}
#[ComplexObject]
impl MyObj {
async fn c(&self) -> i32 {
self.a + self.b
}
}
```