Trait juniper::ScalarValue

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pub trait ScalarValue: Debug + Display + PartialEq + Clone + DeserializeOwned + Serialize + From<String> + From<bool> + From<i32> + From<f64> + 'static {
    // Required methods
    fn as_int(&self) -> Option<i32>;
    fn as_string(&self) -> Option<String>;
    fn into_string(self) -> Option<String>;
    fn as_str(&self) -> Option<&str>;
    fn as_float(&self) -> Option<f64>;
    fn as_bool(&self) -> Option<bool>;

    // Provided methods
    fn is_type<'a, T>(&'a self) -> bool
       where T: 'a,
             Option<&'a T>: From<&'a Self> { ... }
    fn into_another<S: ScalarValue>(self) -> S { ... }
}
Expand description

A trait marking a type that could be used as internal representation of scalar values in juniper

The main objective of this abstraction is to allow other libraries to replace the default representation with something that better fits their needs. There is a custom derive (#[derive(ScalarValue)]) available that implements most of the required traits automatically for a enum representing a scalar value. However, Serialize and Deserialize implementations are expected to be provided.

§Implementing a new scalar value representation

The preferred way to define a new scalar value representation is defining a enum containing a variant for each type that needs to be represented at the lowest level. The following example introduces an new variant that is able to store 64 bit integers.

#[derive(Clone, Debug, PartialEq, ScalarValue, Serialize)]
#[serde(untagged)]
enum MyScalarValue {
    #[value(as_float, as_int)]
    Int(i32),
    Long(i64),
    #[value(as_float)]
    Float(f64),
    #[value(as_str, as_string, into_string)]
    String(String),
    #[value(as_bool)]
    Boolean(bool),
}

impl<'de> Deserialize<'de> for MyScalarValue {
    fn deserialize<D: Deserializer<'de>>(de: D) -> Result<Self, D::Error> {
        struct Visitor;

        impl<'de> de::Visitor<'de> for Visitor {
            type Value = MyScalarValue;

            fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
                f.write_str("a valid input value")
            }

            fn visit_bool<E: de::Error>(self, b: bool) -> Result<Self::Value, E> {
                Ok(MyScalarValue::Boolean(b))
            }

            fn visit_i32<E: de::Error>(self, n: i32) -> Result<Self::Value, E> {
                Ok(MyScalarValue::Int(n))
            }

            fn visit_i64<E: de::Error>(self, n: i64) -> Result<Self::Value, E> {
                if n <= i64::from(i32::MAX) {
                    self.visit_i32(n.try_into().unwrap())
                } else {
                    Ok(MyScalarValue::Long(n))
                }
            }

            fn visit_u32<E: de::Error>(self, n: u32) -> Result<Self::Value, E> {
                if n <= i32::MAX as u32 {
                    self.visit_i32(n.try_into().unwrap())
                } else {
                    self.visit_u64(n.into())
                }
            }

            fn visit_u64<E: de::Error>(self, n: u64) -> Result<Self::Value, E> {
                if n <= i64::MAX as u64 {
                    self.visit_i64(n.try_into().unwrap())
                } else {
                    // Browser's `JSON.stringify()` serialize all numbers
                    // having no fractional part as integers (no decimal
                    // point), so we must parse large integers as floating
                    // point, otherwise we would error on transferring large
                    // floating point numbers.
                    Ok(MyScalarValue::Float(n as f64))
                }
            }

            fn visit_f64<E: de::Error>(self, f: f64) -> Result<Self::Value, E> {
                Ok(MyScalarValue::Float(f))
            }

            fn visit_str<E: de::Error>(self, s: &str) -> Result<Self::Value, E> {
                self.visit_string(s.into())
            }

            fn visit_string<E: de::Error>(self, s: String) -> Result<Self::Value, E> {
                Ok(MyScalarValue::String(s))
            }
        }

        de.deserialize_any(Visitor)
    }
}

Required Methods§

source

fn as_int(&self) -> Option<i32>

Represents this ScalarValue as an integer value.

This function is used for implementing GraphQLValue for i32 for all possible ScalarValues. Implementations should convert all the supported integer types with 32 bit or less to an integer, if requested.

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fn as_string(&self) -> Option<String>

Represents this ScalarValue as a String value.

This function is used for implementing GraphQLValue for String for all possible ScalarValues.

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fn into_string(self) -> Option<String>

Converts this ScalarValue into a String value.

Same as ScalarValue::as_string(), but takes ownership, so allows to omit redundant cloning.

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fn as_str(&self) -> Option<&str>

Represents this ScalarValue as a str value.

This function is used for implementing GraphQLValue for str for all possible ScalarValues.

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fn as_float(&self) -> Option<f64>

Represents this ScalarValue as a float value.

This function is used for implementing GraphQLValue for f64 for all possible ScalarValues. Implementations should convert all supported integer types with 64 bit or less and all floating point values with 64 bit or less to a float, if requested.

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fn as_bool(&self) -> Option<bool>

Represents this ScalarValue as a boolean value

This function is used for implementing GraphQLValue for bool for all possible ScalarValues.

Provided Methods§

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fn is_type<'a, T>(&'a self) -> bool
where T: 'a, Option<&'a T>: From<&'a Self>,

Checks whether this ScalarValue contains the value of the given type.

let value = DefaultScalarValue::Int(42);

assert_eq!(value.is_type::<i32>(), true);
assert_eq!(value.is_type::<f64>(), false);
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fn into_another<S: ScalarValue>(self) -> S

Converts this ScalarValue into another one.

Object Safety§

This trait is not object safe.

Implementors§