Struct frame_support::storage::types::CountedStorageNMap

pub struct CountedStorageNMap<Prefix, Key, Value, QueryKind = OptionQuery, OnEmpty = GetDefault, MaxValues = GetDefault>(/* private fields */);

A wrapper around a StorageNMap and a StorageValue (with the value being u32) to keep track of how many items are in a map, without needing to iterate all the values.

This storage item has some 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.

For general information regarding the #[pallet::storage] attribute, refer to crate::pallet_macros::storage.

Example

#[frame_support::pallet]
mod pallet {
	/// A kitchen-sink CountedStorageNMap, with all possible additional attributes.
    #[pallet::storage]
	#[pallet::getter(fn foo)]
	#[pallet::storage_prefix = "OtherFoo"]
	#[pallet::unbounded]
    pub type Foo<T> = CountedStorageNMap<
		_,
		(
			NMapKey<Blake2_128Concat, u8>,
			NMapKey<Identity, u16>,
			NMapKey<Twox64Concat, u32>
		),
		u64,
		ValueQuery,
	>;

	/// Alternative named syntax.
    #[pallet::storage]
    pub type Bar<T> = CountedStorageNMap<
		Key = (
			NMapKey<Blake2_128Concat, u8>,
			NMapKey<Identity, u16>,
			NMapKey<Twox64Concat, u32>
		),
		Value = u64,
		QueryKind = ValueQuery,
	>;
}

Implementations

impl<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues> CountedStorageNMap<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: CountedStorageNMapInstance, Key: KeyGenerator, Value: FullCodec, QueryKind: QueryKindTrait<Value, OnEmpty>, OnEmpty: Get<QueryKind::Query> + 'static, MaxValues: Get<Option<u32>>,

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

The key used to store the counter of the map.

pub fn map_storage_final_prefix() -> Vec<u8>

The prefix used to generate the key of the map.

pub fn hashed_key_for<KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter>( key: KArg ) -> Vec<u8>

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

pub fn contains_key<KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter>( key: KArg ) -> bool

Does the value (explicitly) exist in storage?

pub fn get<KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter>( key: KArg ) -> QueryKind::Query

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

pub fn try_get<KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter>( key: KArg ) -> Result<Value, ()>

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

Returns Ok if it exists, Err if not.

pub fn set<KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter>( key: KArg, query: QueryKind::Query )

Store or remove the value to be associated with key so that get returns the query. It decrements the counter when the value is removed.

pub fn take<KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter>( key: KArg ) -> QueryKind::Query

Take a value from storage, removing it afterwards.

pub fn swap<KOther, KArg1, KArg2>(key1: KArg1, key2: KArg2)

where KOther: KeyGenerator, KArg1: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter, KArg2: EncodeLikeTuple<KOther::KArg> + TupleToEncodedIter,

Swap the values of two key-pairs.

pub fn insert<KArg, VArg>(key: KArg, val: VArg)

where KArg: EncodeLikeTuple<Key::KArg> + EncodeLike<Key::KArg> + TupleToEncodedIter, VArg: EncodeLike<Value>,

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

pub fn remove<KArg: EncodeLikeTuple<Key::KArg> + EncodeLike<Key::KArg> + TupleToEncodedIter>( key: KArg )

Remove the value under the given keys.

pub fn clear_prefix<KP>( partial_key: KP, limit: u32, maybe_cursor: Option<&[u8]> ) -> MultiRemovalResults

where Key: HasKeyPrefix<KP>,

Attempt to remove items from the map matching a partial_key prefix.

Returns MultiRemovalResults to inform about the result. Once the resultant maybe_cursor field is None, then no further items remain to be deleted.

NOTE: After the initial call for any given map, it is important that no further items are inserted into the map which match the partial key. If so, then the map may not be empty when the resultant maybe_cursor is None.

Limit

A limit must be provided in order to cap the maximum amount of deletions done in a single call. This is one fewer than the maximum number of backend iterations which may be done by this operation and as such represents the maximum number of backend deletions which may happen. A limit of zero implies that no keys will be deleted, though there may be a single iteration done.

Cursor

A cursor may be passed in to this operation with maybe_cursor. None should only be passed once (in the initial call) for any given storage map and partial_key. Subsequent calls operating on the same map/partial_key should always pass Some, and this should be equal to the previous call result’s maybe_cursor field.

pub fn iter_prefix_values<KP>(partial_key: KP) -> PrefixIterator<Value>

where Key: HasKeyPrefix<KP>,

Iterate over values that share the first key.

pub fn mutate<KArg, R, F>(key: KArg, f: F) -> R

where KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter, F: FnOnce(&mut QueryKind::Query) -> R,

Mutate the value under the given keys.

pub fn try_mutate<KArg, R, E, F>(key: KArg, f: F) -> Result<R, E>

where KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter, F: FnOnce(&mut QueryKind::Query) -> Result<R, E>,

Mutate the value under the given keys when the closure returns Ok.

pub fn mutate_exists<KArg, R, F>(key: KArg, f: F) -> R

where KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter, F: FnOnce(&mut Option<Value>) -> R,

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

pub fn try_mutate_exists<KArg, R, E, F>(key: KArg, f: F) -> Result<R, E>

where KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter, 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. 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.

pub fn append<Item, EncodeLikeItem, KArg>(key: KArg, item: EncodeLikeItem)

where KArg: EncodeLikeTuple<Key::KArg> + EncodeLike<Key::KArg> + TupleToEncodedIter, Item: Encode, EncodeLikeItem: EncodeLike<Item>, Value: StorageAppend<Item>,

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 will be overwritten and set to [item]. Any default value set for the storage item will be ignored on overwrite.

pub fn decode_len<KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter>( key: KArg ) -> Option<usize>

where Value: StorageDecodeLength,

Read the length of the storage value without decoding the entire value under the given key1 and key2.

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 completely ignored by this function.

pub fn migrate_keys<KArg>(key: KArg, hash_fns: Key::HArg) -> Option<Value>

where KArg: EncodeLikeTuple<Key::KArg> + TupleToEncodedIter,

Migrate an item with the given key from defunct hash_fns to the current hashers.

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

pub fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> MultiRemovalResults

Attempt to remove all items from the map.

Returns MultiRemovalResults to inform about the result. Once the resultant maybe_cursor field is None, then no further items remain to be deleted.

NOTE: After the initial call for any given map, it is important that no further items are inserted into the map. If so, then the map may not be empty when the resultant maybe_cursor is None.

Limit

A limit must always be provided through in order to cap the maximum amount of deletions done in a single call. This is one fewer than the maximum number of backend iterations which may be done by this operation and as such represents the maximum number of backend deletions which may happen. A limit of zero implies that no keys will be deleted, though there may be a single iteration done.

Cursor

A cursor may be passed in to this operation with maybe_cursor. None should only be passed once (in the initial call) for any given storage map. Subsequent calls operating on the same map should always pass Some, and this should be equal to the previous call result’s maybe_cursor field.

pub fn iter_values() -> PrefixIterator<Value>

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 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() -> Counter

Return the count.

impl<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues> CountedStorageNMap<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: CountedStorageNMapInstance, Key: ReversibleKeyGenerator, Value: FullCodec, QueryKind: QueryKindTrait<Value, OnEmpty>, OnEmpty: Get<QueryKind::Query> + 'static, MaxValues: Get<Option<u32>>,

pub fn iter_prefix<KP>( kp: KP ) -> PrefixIterator<(<Key as HasKeyPrefix<KP>>::Suffix, Value)>

where Key: HasReversibleKeyPrefix<KP>,

Enumerate all elements in the map with prefix key kp in no particular order.

If you add or remove values whose prefix key is kp to the map while doing this, you’ll get undefined results.

pub fn iter_prefix_from<KP>( kp: KP, starting_raw_key: Vec<u8> ) -> PrefixIterator<(<Key as HasKeyPrefix<KP>>::Suffix, Value), OnRemovalCounterUpdate<Prefix>>

where Key: HasReversibleKeyPrefix<KP>,

Enumerate all elements in the map with prefix key kp after a specified starting_raw_key in no particular order.

If you add or remove values whose prefix key is kp to the map while doing this, you’ll get undefined results.

pub fn iter_key_prefix<KP>( kp: KP ) -> KeyPrefixIterator<<Key as HasKeyPrefix<KP>>::Suffix>

where Key: HasReversibleKeyPrefix<KP>,

Enumerate all suffix keys in the map with prefix key kp in no particular order.

If you add or remove values whose prefix key is kp to the map while doing this, you’ll get undefined results.

pub fn iter_key_prefix_from<KP>( kp: KP, starting_raw_key: Vec<u8> ) -> KeyPrefixIterator<<Key as HasKeyPrefix<KP>>::Suffix>

where Key: HasReversibleKeyPrefix<KP>,

Enumerate all suffix keys in the map with prefix key kp after a specified starting_raw_key in no particular order.

If you add or remove values whose prefix key is kp to the map while doing this, you’ll get undefined results.

pub fn drain_prefix<KP>( kp: KP ) -> PrefixIterator<(<Key as HasKeyPrefix<KP>>::Suffix, Value), OnRemovalCounterUpdate<Prefix>>

where Key: HasReversibleKeyPrefix<KP>,

Remove all elements from the map with prefix key kp and iterate through them in no particular order.

If you add elements with prefix key k1 to the map while doing this, you’ll get undefined results.

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

Enumerate all elements in the map in no particular order.

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

pub fn iter_from( starting_raw_key: Vec<u8> ) -> PrefixIterator<(Key::Key, Value), OnRemovalCounterUpdate<Prefix>>

Enumerate all elements in the map after a specified starting_key in no particular order.

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

pub fn iter_keys() -> KeyPrefixIterator<Key::Key>

Enumerate all keys in the map in no particular order.

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

pub fn iter_keys_from(starting_raw_key: Vec<u8>) -> KeyPrefixIterator<Key::Key>

Enumerate all keys in the map after a specified starting_raw_key in no particular order.

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

pub fn drain( ) -> PrefixIterator<(Key::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::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 can’t be decoded because the storage is corrupted, then it is skipped.

Trait Implementations

impl<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues> PartialStorageInfoTrait for CountedStorageNMap<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: CountedStorageNMapInstance, Key: KeyGenerator, 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, Key, Value, QueryKind, OnEmpty, MaxValues> StorageEntryMetadataBuilder for CountedStorageNMap<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: CountedStorageNMapInstance, Key: KeyGenerator, Value: FullCodec + StaticTypeInfo, QueryKind: QueryKindTrait<Value, OnEmpty>, OnEmpty: Get<QueryKind::Query> + 'static, MaxValues: Get<Option<u32>>,

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

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

impl<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues> StorageInfoTrait for CountedStorageNMap<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: CountedStorageNMapInstance, Key: KeyGenerator + KeyGeneratorMaxEncodedLen, Value: FullCodec + MaxEncodedLen, QueryKind: QueryKindTrait<Value, OnEmpty>, OnEmpty: Get<QueryKind::Query> + 'static, MaxValues: Get<Option<u32>>,

fn storage_info() -> Vec<StorageInfo>

impl<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues> TryDecodeEntireStorage for CountedStorageNMap<Prefix, Key, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: CountedStorageNMapInstance, Key: KeyGenerator, Value: FullCodec, QueryKind: QueryKindTrait<Value, OnEmpty>, OnEmpty: Get<QueryKind::Query> + 'static, MaxValues: Get<Option<u32>>,

fn try_decode_entire_state() -> Result<usize, Vec<TryDecodeEntireStorageError>>

Decode the entire data under the given storage, returning Ok(bytes_decoded) if success.