[][src]Trait frame_support::storage::StorageValue

pub trait StorageValue<T: FullCodec> {
    type Query;
    pub fn hashed_key() -> [u8; 32];
pub fn exists() -> bool;
pub fn get() -> Self::Query;
pub fn try_get() -> Result<T, ()>;
pub fn translate<O: Decode, F: FnOnce(Option<O>) -> Option<T>>(
        f: F
    ) -> Result<Option<T>, ()>;
pub fn put<Arg: EncodeLike<T>>(val: Arg);
pub fn set(val: Self::Query);
pub fn mutate<R, F: FnOnce(&mut Self::Query) -> R>(f: F) -> R;
pub fn try_mutate<R, E, F: FnOnce(&mut Self::Query) -> Result<R, E>>(
        f: F
    ) -> Result<R, E>;
pub fn kill();
pub fn take() -> Self::Query;
pub fn append<Item, EncodeLikeItem>(item: EncodeLikeItem)
    where
        Item: Encode,
        EncodeLikeItem: EncodeLike<Item>,
        T: StorageAppend<Item>
; pub fn decode_len() -> Option<usize>
    where
        T: StorageDecodeLength
, { ... } }

A trait for working with macro-generated storage values under the substrate storage API.

Details on implementation can be found at [generator::StorageValue]

Associated Types

type Query

The type that get/take return.

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Required methods

pub fn hashed_key() -> [u8; 32]

Get the storage key.

pub fn exists() -> bool

Does the value (explicitly) exist in storage?

pub fn get() -> Self::Query

Load the value from the provided storage instance.

pub fn try_get() -> Result<T, ()>

Try to get the underlying value from the provided storage instance; Ok if it exists, Err if not.

pub fn translate<O: Decode, F: FnOnce(Option<O>) -> Option<T>>(
    f: F
) -> Result<Option<T>, ()>

Translate a value from some previous type (O) to the current type.

f: F is the translation function.

Returns Err if the storage item could not be interpreted as the old type, and Ok, along with the new value if it could.

NOTE: This operates from and to Option<_> types; no effort is made to respect the default value of the original type.

Warning

This function must be used with care, before being updated the storage still contains the old type, thus other calls (such as get) will fail at decoding it.

Usage

This would typically be called inside the module implementation of on_runtime_upgrade, while ensuring no usage of this storage are made before the call to on_runtime_upgrade. (More precisely prior initialized modules doesn't make use of this storage).

pub fn put<Arg: EncodeLike<T>>(val: Arg)

Store a value under this key into the provided storage instance.

pub fn set(val: Self::Query)

Store a value under this key into the provided storage instance; this uses the query type rather than the underlying value.

pub fn mutate<R, F: FnOnce(&mut Self::Query) -> R>(f: F) -> R

Mutate the value

pub fn try_mutate<R, E, F: FnOnce(&mut Self::Query) -> Result<R, E>>(
    f: F
) -> Result<R, E>

Mutate the value if closure returns Ok

pub fn kill()

Clear the storage value.

pub fn take() -> Self::Query

Take a value from storage, removing it afterwards.

pub fn append<Item, EncodeLikeItem>(item: EncodeLikeItem) where
    Item: Encode,
    EncodeLikeItem: EncodeLike<Item>,
    T: StorageAppend<Item>, 

Append the given item to the value in the storage.

T is required to implement StorageAppend.

Warning

If the storage item is not encoded properly, the storage item will be overwritten and set to [item]. Any default value set for the storage item will be ignored on overwrite.

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Provided methods

pub fn decode_len() -> Option<usize> where
    T: StorageDecodeLength

Read the length of the storage value without decoding the entire value.

T is required to implement StorageDecodeLength.

If the value does not exists or it fails to decode the length, None is returned. Otherwise Some(len) is returned.

Warning

None does not mean that get() does not return a value. The default value is completly ignored by this function.

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Implementors

impl<T: FullCodec, G: StorageValue<T>> StorageValue<T> for G[src]

type Query = G::Query

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