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Reword guide-level explanation of optional query parameters.

This commit is contained in:
Damir Vandic 2019-01-18 14:49:28 +01:00 committed by Jeb Rosen
parent c86f4312fb
commit ecc17d191f
1 changed files with 8 additions and 10 deletions
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18
site/guide/4-requests.md
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@ -276,14 +276,9 @@ string contains all of the static components of a route's query string, the
request will be routed to that route. This allows for optional parameters,
validating even when a parameter is missing.
More specifically, types that return `Some` from their
[`FromFormValue::default()`] implementations will validate even when a value for
the given parameter is missing, using the value returned from the `default()`
method as the parameter's value. On such type is `Option<T>`, which returns
`None` from its `default()` implementation. By using a type of `Option<T>` for a
query parameter, `Some(T)` will be returned only when the parameter is present
and represents a valid `T`. In all other cases, `None` will be returned. A route
using `Option<T>` looks as follows:
To achieve this, use `Option<T>` as the parameter type. Whenever the query
parameter is missing in a request, `None` will be provided as the value. A
route using `Option<T>` looks as follows:
```rust
#[get("/hello?wave&<name>")]
@ -298,8 +293,11 @@ routed to this route. If a `name=value` query segment is present, the route
returns the string `"Hi, value!"`. If no `name` query segment is present, the
route returns `"Hello!"`.
Other defaultable `FromFormValue` types include `Result<T, E>` and `bool`. As
always, your types can implement `FromFormValue` in a defaultable manner, too!
Just like a parameter of type `Option<T>` will have the value `None` if the
parameter is missing from a query, a parameter of type `bool` will have the
value `false` if it is missing. The default value for a missing parameter can be
customized for your own types that implement `FromFormValue` by implementing
[`FromFormValue::default()`].
[`FromFormValue::default()`]: @api/rocket/request/trait.FromFormValue.html#method.default