Trait frame_support::storage::StorageMap

pub trait StorageMap<K: FullEncode, V: FullCodec> {
    type Query;

    // Required methods
    fn hashed_key_for<KeyArg: EncodeLike<K>>(key: KeyArg) -> Vec<u8> ;
    fn contains_key<KeyArg: EncodeLike<K>>(key: KeyArg) -> bool;
    fn get<KeyArg: EncodeLike<K>>(key: KeyArg) -> Self::Query;
    fn set<KeyArg: EncodeLike<K>>(key: KeyArg, query: Self::Query);
    fn try_get<KeyArg: EncodeLike<K>>(key: KeyArg) -> Result<V, ()>;
    fn swap<KeyArg1: EncodeLike<K>, KeyArg2: EncodeLike<K>>(
        key1: KeyArg1,
        key2: KeyArg2
    );
    fn insert<KeyArg: EncodeLike<K>, ValArg: EncodeLike<V>>(
        key: KeyArg,
        val: ValArg
    );
    fn remove<KeyArg: EncodeLike<K>>(key: KeyArg);
    fn mutate<KeyArg: EncodeLike<K>, R, F: FnOnce(&mut Self::Query) -> R>(
        key: KeyArg,
        f: F
    ) -> R;
    fn try_mutate<KeyArg: EncodeLike<K>, R, E, F: FnOnce(&mut Self::Query) -> Result<R, E>>(
        key: KeyArg,
        f: F
    ) -> Result<R, E>;
    fn mutate_exists<KeyArg: EncodeLike<K>, R, F: FnOnce(&mut Option<V>) -> R>(
        key: KeyArg,
        f: F
    ) -> R;
    fn try_mutate_exists<KeyArg: EncodeLike<K>, R, E, F: FnOnce(&mut Option<V>) -> Result<R, E>>(
        key: KeyArg,
        f: F
    ) -> Result<R, E>;
    fn take<KeyArg: EncodeLike<K>>(key: KeyArg) -> Self::Query;
    fn append<Item, EncodeLikeItem, EncodeLikeKey>(
        key: EncodeLikeKey,
        item: EncodeLikeItem
    )
       where EncodeLikeKey: EncodeLike<K>,
             Item: Encode,
             EncodeLikeItem: EncodeLike<Item>,
             V: StorageAppend<Item>;
    fn migrate_key<OldHasher: StorageHasher, KeyArg: EncodeLike<K>>(
        key: KeyArg
    ) -> Option<V>;

    // Provided methods
    fn mutate_extant<KeyArg: EncodeLike<K>, R: Default, F: FnOnce(&mut V) -> R>(
        key: KeyArg,
        f: F
    ) -> R { ... }
    fn decode_len<KeyArg: EncodeLike<K>>(key: KeyArg) -> Option<usize>
       where V: StorageDecodeLength { ... }
    fn migrate_key_from_blake<KeyArg: EncodeLike<K>>(key: KeyArg) -> Option<V> { ... }
}

A strongly-typed map in storage.

Details on implementation can be found at [generator::StorageMap].

Required Associated Types

type Query

The type that get/take return.

Required Methods

fn hashed_key_for<KeyArg: EncodeLike<K>>(key: KeyArg) -> Vec<u8>

Get the storage key used to fetch a value corresponding to a specific key.

fn contains_key<KeyArg: EncodeLike<K>>(key: KeyArg) -> bool

Does the value (explicitly) exist in storage?

fn get<KeyArg: EncodeLike<K>>(key: KeyArg) -> Self::Query

Load the value associated with the given key from the map.

fn set<KeyArg: EncodeLike<K>>(key: KeyArg, query: Self::Query)

Store or remove the value to be associated with key so that get returns the query.

fn try_get<KeyArg: EncodeLike<K>>(key: KeyArg) -> Result<V, ()>

Try to get the value for the given key from the map.

Returns Ok if it exists, Err if not.

fn swap<KeyArg1: EncodeLike<K>, KeyArg2: EncodeLike<K>>( key1: KeyArg1, key2: KeyArg2 )

Swap the values of two keys.

fn insert<KeyArg: EncodeLike<K>, ValArg: EncodeLike<V>>( key: KeyArg, val: ValArg )

Store a value to be associated with the given key from the map.

fn remove<KeyArg: EncodeLike<K>>(key: KeyArg)

Remove the value under a key.

fn mutate<KeyArg: EncodeLike<K>, R, F: FnOnce(&mut Self::Query) -> R>( key: KeyArg, f: F ) -> R

Mutate the value under a key.

fn try_mutate<KeyArg: EncodeLike<K>, R, E, F: FnOnce(&mut Self::Query) -> Result<R, E>>( key: KeyArg, f: F ) -> Result<R, E>

Mutate the item, only if an Ok value is returned.

fn mutate_exists<KeyArg: EncodeLike<K>, R, F: FnOnce(&mut Option<V>) -> R>( key: KeyArg, f: F ) -> R

Mutate the value under a key.

Deletes the item if mutated to a None.

fn try_mutate_exists<KeyArg: EncodeLike<K>, R, E, F: FnOnce(&mut Option<V>) -> Result<R, E>>( key: KeyArg, f: F ) -> Result<R, E>

Mutate the item, only if an Ok value is returned. Deletes the item if mutated to a None. f will always be called with an option representing if the storage item exists (Some<V>) or if the storage item does not exist (None), independent of the QueryType.

fn take<KeyArg: EncodeLike<K>>(key: KeyArg) -> Self::Query

Take the value under a key.

fn append<Item, EncodeLikeItem, EncodeLikeKey>( key: EncodeLikeKey, item: EncodeLikeItem )where EncodeLikeKey: EncodeLike<K>, Item: Encode, EncodeLikeItem: EncodeLike<Item>, V: StorageAppend<Item>,

Append the given items to the value in the storage.

V is required to implement codec::EncodeAppend.

Warning

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

fn migrate_key<OldHasher: StorageHasher, KeyArg: EncodeLike<K>>( key: KeyArg ) -> Option<V>

Migrate an item with the given key from a defunct OldHasher to the current hasher.

If the key doesn’t exist, then it’s a no-op. If it does, then it returns its value.

Provided Methods

fn mutate_extant<KeyArg: EncodeLike<K>, R: Default, F: FnOnce(&mut V) -> R>( key: KeyArg, f: F ) -> R

Mutate the value under a key if the value already exists. Do nothing and return the default value if not.

fn decode_len<KeyArg: EncodeLike<K>>(key: KeyArg) -> Option<usize>where V: StorageDecodeLength,

Read the length of the storage value without decoding the entire value under the given key.

V 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.

fn migrate_key_from_blake<KeyArg: EncodeLike<K>>(key: KeyArg) -> Option<V>

Migrate an item with the given key from a blake2_256 hasher to the current hasher.

If the key doesn’t exist, then it’s a no-op. If it does, then it returns its value.

Implementors

impl<K: FullEncode, V: FullCodec, G: StorageMap<K, V>> StorageMap<K, V> for G

type Query = <G as StorageMap<K, V>>::Query