[−][src]Trait juniper::ScalarValue

pub trait ScalarValue: Debug + Display + PartialEq + Clone + Serialize + From<String> + From<bool> + From<i32> + From<f64> + 'static {
    type Visitor: for<'de> Visitor<'de, Value = Self> + Default;
    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_boolean(&self) -> Option<bool>;

    fn is_type<'a, T>(&'a self) -> bool
    where
        T: 'a,
        &'a Self: Into<Option<&'a T>>,
    { ... }

    fn into_another<S: ScalarValue>(self) -> S { ... }
}

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(juniper::GraphQLScalarValue)]) available that implements most of the required traits automatically for a enum representing a scalar value. This derives needs a additional annotation of the form #[juniper(visitor = "VisitorType")] to specify a type that implements serde::de::Visitor and that is used to deserialize the value.

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(Debug, Clone, PartialEq, juniper::GraphQLScalarValue)]
enum MyScalarValue {
    Int(i32),
    Long(i64),
    Float(f64),
    String(String),
    Boolean(bool),
}

impl ScalarValue for MyScalarValue {
    type Visitor = MyScalarValueVisitor;

     fn as_int(&self) -> Option<i32> {
       match *self {
           Self::Int(ref i) => Some(*i),
           _ => None,
       }
   }

   fn as_string(&self) -> Option<String> {
       match *self {
           Self::String(ref s) => Some(s.clone()),
           _ => None,
       }
   }

   fn into_string(self) -> Option<String> {
       match self {
           Self::String(s) => Some(s),
           _ => None,
       }
   }

   fn as_str(&self) -> Option<&str> {
       match *self {
           Self::String(ref s) => Some(s.as_str()),
           _ => None,
       }
   }

   fn as_float(&self) -> Option<f64> {
       match *self {
           Self::Int(ref i) => Some(*i as f64),
           Self::Float(ref f) => Some(*f),
           _ => None,
       }
   }

   fn as_boolean(&self) -> Option<bool> {
       match *self {
           Self::Boolean(ref b) => Some(*b),
           _ => None,
       }
   }
}

#[derive(Default)]
struct MyScalarValueVisitor;

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

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

    fn visit_bool<E>(self, value: bool) -> Result<MyScalarValue, E> {
        Ok(MyScalarValue::Boolean(value))
    }

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

    fn visit_i64<E>(self, value: i64) -> Result<MyScalarValue, E>
    where
        E: de::Error,
    {
        if value <= i32::max_value() as i64 {
            self.visit_i32(value as i32)
        } else {
            Ok(MyScalarValue::Long(value))
        }
    }

    fn visit_u32<E>(self, value: u32) -> Result<MyScalarValue, E>
    where
        E: de::Error,
    {
        if value <= i32::max_value() as u32 {
            self.visit_i32(value as i32)
        } else {
            self.visit_u64(value as u64)
        }
    }

    fn visit_u64<E>(self, value: u64) -> Result<MyScalarValue, E>
    where
        E: de::Error,
    {
        if value <= i64::max_value() as u64 {
            self.visit_i64(value as i64)
        } 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(value as f64))
        }
    }

    fn visit_f64<E>(self, value: f64) -> Result<MyScalarValue, E> {
        Ok(MyScalarValue::Float(value))
    }

    fn visit_str<E>(self, value: &str) -> Result<MyScalarValue, E>
    where
        E: de::Error,
    {
        self.visit_string(value.into())
    }

    fn visit_string<E>(self, value: String) -> Result<MyScalarValue, E> {
        Ok(MyScalarValue::String(value))
    }
}

Associated Types

type Visitor: for<'de> Visitor<'de, Value = Self> + Default[src]

Serde visitor used to deserialize this scalar value

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Required methods

fn as_int(&self) -> Option<i32>[src]

Convert the given scalar value into an integer value

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

fn as_string(&self) -> Option<String>[src]

Represents this ScalarValue a String value.

This function is used for implementing GraphQLValue for String for all scalar values

fn into_string(self) -> Option<String>[src]

Converts this ScalarValue into a String value.

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

fn as_str(&self) -> Option<&str>[src]

Convert the given scalar value into a string value

This function is used for implementing GraphQLValue for String for all scalar values

fn as_float(&self) -> Option<f64>[src]

Convert the given scalar value into a float value

This function is used for implementing GraphQLValue for f64 for all scalar values. 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.

fn as_boolean(&self) -> Option<bool>[src]

Convert the given scalar value into a boolean value

This function is used for implementing GraphQLValue for bool for all scalar values.

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Provided methods

fn is_type<'a, T>(&'a self) -> bool where
    T: 'a,
    &'a Self: Into<Option<&'a T>>, [src]

Checks if the current value contains the a value of the current type


let value = DefaultScalarValue::Int(42);

assert_eq!(value.is_type::<i32>(), true);
assert_eq!(value.is_type::<f64>(), false);

fn into_another<S: ScalarValue>(self) -> S[src]

Converts this ScalarValue into another one.

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Implementors

impl ScalarValue for DefaultScalarValue[src]

type Visitor = DefaultScalarValueVisitor

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