# query.fields.OneRelation.is

- **Module:** query.fields.OneRelation
- **Package:** libtmux
- **Language:** Rust
- **Kind:** method
- **Source:** https://github.com/libtmux/libtmux-rs/blob/f0e37052c232636b61d095817046e6bfc8f2ca40/crates/libtmux/src/query/fields.rs#L240
- **Page:** https://libtmux.org/en/rs/latest/reference/query-fields-onerelation-is/

```
query.fields.OneRelation.is(self, expression: FilterExpr<To>) -> FilterExpr<From>
```

Match when the related candidate exists and satisfies `expression`.

## Example

```rust
use libtmux::query::{BoolField, OneRelation};
use libtmux::query::__private;

struct Parent;
struct Child;
let relation: OneRelation<Parent, Child> =
    __private::one_relation("parent", "child");
let done: BoolField<Child> = __private::bool_field("child", "done");
assert_eq!(relation.is(done.eq(true)), relation.is(done.eq(true)));
```