Struct frame_support::storage::types::CountedStorageMap

pub struct CountedStorageMap<Prefix, Hasher, Key, Value, QueryKind = OptionQuery, OnEmpty = GetDefault, MaxValues = GetDefault>(_);

A wrapper around a StorageMap and a StorageValue<Value=u32> to keep track of how many items are in a map, without needing to iterate all the values.

This storage item has additional storage read and write overhead when manipulating values compared to a regular storage map.

For functions where we only add or remove a value, a single storage read is needed to check if that value already exists. For mutate functions, two storage reads are used to check if the value existed before and after the mutation.

Whenever the counter needs to be updated, an additional read and write occurs to update that counter.

Implementations

impl<Prefix, Hasher, Key, Value, QueryKind, OnEmpty, MaxValues> CountedStorageMap<Prefix, Hasher, Key, Value, QueryKind, OnEmpty, MaxValues> where
    Prefix: CountedStorageMapInstance,
    Hasher: StorageHasher,
    Key: FullCodec,
    Value: FullCodec,
    QueryKind: QueryKindTrait<Value, OnEmpty>,
    OnEmpty: Get<QueryKind::Query> + 'static,
    MaxValues: Get<Option<u32>>, 

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

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

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

Does the value (explicitly) exist in storage?

pub fn get<KeyArg: EncodeLike<Key>>(key: KeyArg) -> QueryKind::Query

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

pub fn try_get<KeyArg: EncodeLike<Key>>(key: KeyArg) -> Result<Value, ()>

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

Returns Ok if it exists, Err if not.

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

Swap the values of two keys.

pub fn insert<KeyArg: EncodeLike<Key> + Clone, ValArg: EncodeLike<Value>>(
    key: KeyArg,
    val: ValArg
)

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

pub fn remove<KeyArg: EncodeLike<Key> + Clone>(key: KeyArg)

Remove the value under a key.

pub fn mutate<KeyArg: EncodeLike<Key> + Clone, R, F: FnOnce(&mut QueryKind::Query) -> R>(
    key: KeyArg,
    f: F
) -> R

Mutate the value under a key.

pub fn try_mutate<KeyArg, R, E, F>(key: KeyArg, f: F) -> Result<R, E> where
    KeyArg: EncodeLike<Key> + Clone,
    F: FnOnce(&mut QueryKind::Query) -> Result<R, E>, 

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

pub fn mutate_exists<KeyArg: EncodeLike<Key> + Clone, R, F: FnOnce(&mut Option<Value>) -> R>(
    key: KeyArg,
    f: F
) -> R

Mutate the value under a key. Deletes the item if mutated to a None.

pub fn try_mutate_exists<KeyArg, R, E, F>(key: KeyArg, f: F) -> Result<R, E> where
    KeyArg: EncodeLike<Key> + Clone,
    F: FnOnce(&mut Option<Value>) -> Result<R, E>, 

Mutate the item, only if an Ok value is returned. Deletes the item if mutated to a None.

pub fn take<KeyArg: EncodeLike<Key> + Clone>(key: KeyArg) -> QueryKind::Query

Take the value under a key.

pub fn append<Item, EncodeLikeItem, EncodeLikeKey>(
    key: EncodeLikeKey,
    item: EncodeLikeItem
) where
    EncodeLikeKey: EncodeLike<Key> + Clone,
    Item: Encode,
    EncodeLikeItem: EncodeLike<Item>,
    Value: StorageAppend<Item>, 

Append the given items to the value in the storage.

Value 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.

pub fn decode_len<KeyArg: EncodeLike<Key>>(key: KeyArg) -> Option<usize> where
    Value: StorageDecodeLength, 

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

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.

pub fn migrate_key<OldHasher: StorageHasher, KeyArg: EncodeLike<Key>>(
    key: KeyArg
) -> Option<Value>

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.

pub fn remove_all(maybe_limit: Option<u32>)

Remove all value of the storage.

pub fn iter_values() -> PrefixIterator<Value, OnRemovalCounterUpdate<Prefix>>

Iter over all value of the storage.

NOTE: If a value failed to decode because storage is corrupted then it is skipped.

pub fn translate_values<OldValue: Decode, F: FnMut(OldValue) -> Option<Value>>(
    f: F
)

Translate the values of all elements by a function f, in the map in no particular order.

By returning None from f for an element, you’ll remove it from the map.

NOTE: If a value fail to decode because storage is corrupted then it is skipped.

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.

pub fn try_append<KArg, Item, EncodeLikeItem>(
    key: KArg,
    item: EncodeLikeItem
) -> Result<(), ()> where
    KArg: EncodeLike<Key> + Clone,
    Item: Encode,
    EncodeLikeItem: EncodeLike<Item>,
    Value: StorageTryAppend<Item>, 

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

Is only available if Value of the storage implements StorageTryAppend.

pub fn initialize_counter() -> u32

Initialize the counter with the actual number of items in the map.

This function iterates through all the items in the map and sets the counter. This operation can be very heavy, so use with caution.

Returns the number of items in the map which is used to set the counter.

pub fn count() -> u32

Return the count.

impl<Prefix, Hasher, Key, Value, QueryKind, OnEmpty, MaxValues> CountedStorageMap<Prefix, Hasher, Key, Value, QueryKind, OnEmpty, MaxValues> where
    Prefix: CountedStorageMapInstance,
    Hasher: StorageHasher + ReversibleStorageHasher,
    Key: FullCodec,
    Value: FullCodec,
    QueryKind: QueryKindTrait<Value, OnEmpty>,
    OnEmpty: Get<QueryKind::Query> + 'static,
    MaxValues: Get<Option<u32>>, 

pub fn iter() -> PrefixIterator<(Key, Value), OnRemovalCounterUpdate<Prefix>>

Enumerate all elements in the map in no particular order.

If you alter the map while doing this, you’ll get undefined results.

pub fn drain() -> PrefixIterator<(Key, Value), OnRemovalCounterUpdate<Prefix>>

Remove all elements from the map and iterate through them in no particular order.

If you add elements to the map while doing this, you’ll get undefined results.

pub fn translate<O: Decode, F: FnMut(Key, O) -> Option<Value>>(f: F)

Translate the values of all elements by a function f, in the map in no particular order.

By returning None from f for an element, you’ll remove it from the map.

NOTE: If a value fail to decode because storage is corrupted then it is skipped.

Trait Implementations

impl<Prefix, Hasher, Key, Value, QueryKind, OnEmpty, MaxValues> PartialStorageInfoTrait for CountedStorageMap<Prefix, Hasher, Key, Value, QueryKind, OnEmpty, MaxValues> where
    Prefix: CountedStorageMapInstance,
    Hasher: StorageHasher,
    Key: FullCodec,
    Value: FullCodec,
    QueryKind: QueryKindTrait<Value, OnEmpty>,
    OnEmpty: Get<QueryKind::Query> + 'static,
    MaxValues: Get<Option<u32>>, 

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

fn partial_storage_info() -> Vec<StorageInfo>

impl<Prefix, Hasher, Key, Value, QueryKind, OnEmpty, MaxValues> StorageEntryMetadataBuilder for CountedStorageMap<Prefix, Hasher, Key, Value, QueryKind, OnEmpty, MaxValues> where
    Prefix: CountedStorageMapInstance,
    Hasher: StorageHasher,
    Key: FullCodec + StaticTypeInfo,
    Value: FullCodec + StaticTypeInfo,
    QueryKind: QueryKindTrait<Value, OnEmpty>,
    OnEmpty: Get<QueryKind::Query> + 'static,
    MaxValues: Get<Option<u32>>, 

fn build_metadata(
    docs: Vec<&'static str>,
    entries: &mut Vec<StorageEntryMetadata>
)

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

impl<Prefix, Hasher, Key, Value, QueryKind, OnEmpty, MaxValues> StorageInfoTrait for CountedStorageMap<Prefix, Hasher, Key, Value, QueryKind, OnEmpty, MaxValues> where
    Prefix: CountedStorageMapInstance,
    Hasher: StorageHasher,
    Key: FullCodec + MaxEncodedLen,
    Value: FullCodec + MaxEncodedLen,
    QueryKind: QueryKindTrait<Value, OnEmpty>,
    OnEmpty: Get<QueryKind::Query> + 'static,
    MaxValues: Get<Option<u32>>, 

fn storage_info() -> Vec<StorageInfo>