# Input value validators
Arguments to a query ([InputObject](define_input_object.md)) are called `Input Objects` in GraphQL. If the provided input type does not match for a query, the query will return a type mismatch error. But sometimes we want to provide more restrictions on specific types of values. For example, we might want to require that an argument is a valid email address. `Async-graphql` provides an input validators to solve this problem.
An input validator can be combined via `and` and `or` operators.
The following is an input validator which checks that a `String` is a valid Email or MAC address:
```rust
use async_graphql::*;
use async_graphql::validators::{Email, MAC};
struct Query;
#[Object]
impl Query {
async fn input(#[graphql(validator(or(Email, MAC(colon = "false"))))] a: String) {
}
}
```
The following example verifies that the `i32` parameter `a` is greater than 10 and less than 100, or else equal to 0:
```rust
use async_graphql:*;
use async_graphql::validators::{IntGreaterThan, IntLessThan, IntEqual};
struct Query;
#[Object]
impl Query {
async fn input(#[validator(
or(
and(IntGreaterThan(value = "10"), IntLessThan(value = "100")),
IntEqual(value = "0")
))] a: String) {
} {
}
}
```
## Custom validator
Here is an example of a custom validator:
```rust
struct MustBeZero {}
impl InputValueValidator for MustBeZero {
fn is_valid(&self, value: &Value) -> Result<(), String> {
if let Value::Int(n) = value {
if n.as_i64().unwrap() != 0 {
// Validation failed
Err(format!(
"the value is {}, but must be zero",
n.as_i64().unwrap(),
))
} else {
// Validation succeeded
Ok(())
}
} else {
// If the type does not match we can return None and built-in validations
// will pick up on the error
Ok(())
}
}
}
```