Struct frame_support::pallet_prelude::StorageValue[][src]

pub struct StorageValue<Prefix, Value, QueryKind = OptionQuery, OnEmpty = GetDefault>(_);
Expand description

A type that allow to store a value.

Each value is stored at:

Twox128(Prefix::pallet_prefix()) ++ Twox128(Prefix::STORAGE_PREFIX)

Implementations

Get the storage key.

Does the value (explicitly) exist in storage?

Load the value from the provided storage instance.

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

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).

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

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

this uses the query type rather than the underlying value.

Mutate the value

Mutate the value if closure returns Ok

Clear the storage value.

Take a value from storage, removing it afterwards.

Append the given item to the value in the storage.

Value 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.

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

Value 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.

Try and append the given item to the value in the storage.

Is only available if Value of the storage implements StorageTryAppend.

Trait Implementations

It doesn’t require to implement MaxEncodedLen and give no information for max_size.

Build into entries the storage metadata entries of a storage given some docs.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Convert from a value of T into an equivalent instance of Option<Self>. Read more

Consume self to return Some equivalent value of Option<T>. Read more

Convert Box<dyn Trait> (where Trait: Downcast) to Box<dyn Any>. Box<dyn Any> can then be further downcast into Box<ConcreteType> where ConcreteType implements Trait. Read more

Convert Rc<Trait> (where Trait: Downcast) to Rc<Any>. Rc<Any> can then be further downcast into Rc<ConcreteType> where ConcreteType implements Trait. Read more

Convert &Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &Any’s vtable from &Trait’s. Read more

Convert &mut Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &mut Any’s vtable from &mut Trait’s. Read more

Convert Arc<Trait> (where Trait: Downcast) to Arc<Any>. Arc<Any> can then be further downcast into Arc<ConcreteType> where ConcreteType implements Trait. Read more

Performs the conversion.

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more

Instruments this type with the current Span, returning an Instrumented wrapper. Read more

Performs the conversion.

Get a reference to the inner from the outer.

Get a mutable reference to the inner from the outer.

Should always be Self

Convert from a value of T into an equivalent instance of Self. Read more

Consume self to return an equivalent value of T. Read more

The type that get/take return.

Get the storage key.

Does the value (explicitly) exist in storage?

Load the value from the provided storage instance.

Try to get the underlying value from the provided storage instance. Read more

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

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

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

Clear the storage value.

Mutate the value

Mutate the value if closure returns Ok

Take a value from storage, removing it afterwards.

Append the given item to the value in the storage. Read more

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

Try and append the item into the storage item. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.

The counterpart to unchecked_from.

Consume self to return an equivalent value of T.

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more