Struct frame_support::storage::types::StorageDoubleMap

pub struct StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind = OptionQuery, OnEmpty = GetDefault, MaxValues = GetDefault>(/* private fields */);

A type representing a double map in storage. This structure associates a pair of keys with a value of a specified type stored on-chain.

A double map with keys k1 and k2 can be likened to a StorageMap with a key of type (k1, k2). However, a double map offers functions specific to each key, enabling partial iteration and deletion based on one key alone.

Also, conceptually, a double map is a special case of a StorageNMap using two keys.

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

Examples

Kitchen-sink

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

	/// Alternative named syntax.
    #[pallet::storage]
    pub type Bar<T> = StorageDoubleMap<
        Hasher1 = Blake2_128Concat,
        Key1 = u8,
        Hasher2 = Twox64Concat,
        Key2 = u16,
        Value = u32,
        QueryKind = ValueQuery
    >;
}

Partial Iteration & Removal

When Hasher1 and Hasher2 implement the ReversibleStorageHasher trait, the first key k1 can be used to partially iterate over keys and values of the double map, and to delete items.

#[test]
fn example_double_map_partial_operations() {
	type FooDoubleMap =
		StorageDoubleMap<Prefix, Blake2_128Concat, u32, Blake2_128Concat, u32, u32, ValueQuery>;

	TestExternalities::default().execute_with(|| {
		FooDoubleMap::insert(0, 0, 42);
		FooDoubleMap::insert(0, 1, 43);
		FooDoubleMap::insert(1, 0, 314);

		// should be equal to {0,1} (ordering is random)
		let collected_k2_keys: BTreeSet<_> = FooDoubleMap::iter_key_prefix(0).collect();
		assert_eq!(collected_k2_keys, [0, 1].iter().copied().collect::<BTreeSet<_>>());

		// should be equal to {42,43} (ordering is random)
		let collected_k2_values: BTreeSet<_> = FooDoubleMap::iter_prefix_values(0).collect();
		assert_eq!(collected_k2_values, [42, 43].iter().copied().collect::<BTreeSet<_>>());

		// Remove items from the map using k1 = 0
		let _ = FooDoubleMap::clear_prefix(0, u32::max_value(), None);
		// Values associated with (0, _) should have been removed
		assert_eq!(FooDoubleMap::iter_prefix(0).collect::<Vec<_>>(), vec![]);
	});
}

Implementations

impl<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues> StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: StorageInstance, Hasher1: StorageHasher, Hasher2: StorageHasher, Key1: FullCodec, Key2: FullCodec, Value: FullCodec, QueryKind: QueryKindTrait<Value, OnEmpty>, OnEmpty: Get<QueryKind::Query> + 'static, MaxValues: Get<Option<u32>>,

pub fn hashed_key_for<KArg1, KArg2>(k1: KArg1, k2: KArg2) -> Vec<u8>

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>,

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

pub fn contains_key<KArg1, KArg2>(k1: KArg1, k2: KArg2) -> bool

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>,

Does the value (explicitly) exist in storage?

pub fn get<KArg1, KArg2>(k1: KArg1, k2: KArg2) -> QueryKind::Query

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>,

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

pub fn try_get<KArg1, KArg2>(k1: KArg1, k2: KArg2) -> Result<Value, ()>

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>,

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

Returns Ok if it exists, Err if not.

pub fn set<KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>>( k1: KArg1, k2: KArg2, q: QueryKind::Query, )

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

pub fn take<KArg1, KArg2>(k1: KArg1, k2: KArg2) -> QueryKind::Query

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>,

Take a value from storage, removing it afterwards.

pub fn swap<XKArg1, XKArg2, YKArg1, YKArg2>( x_k1: XKArg1, x_k2: XKArg2, y_k1: YKArg1, y_k2: YKArg2, )

where XKArg1: EncodeLike<Key1>, XKArg2: EncodeLike<Key2>, YKArg1: EncodeLike<Key1>, YKArg2: EncodeLike<Key2>,

Swap the values of two key-pairs.

pub fn insert<KArg1, KArg2, VArg>(k1: KArg1, k2: KArg2, val: VArg)

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>, VArg: EncodeLike<Value>,

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

pub fn remove<KArg1, KArg2>(k1: KArg1, k2: KArg2)

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>,

Remove the value under the given keys.

pub fn remove_prefix<KArg1>(k1: KArg1, limit: Option<u32>) -> KillStorageResult

where KArg1: ?Sized + EncodeLike<Key1>,

👎Deprecated: Use clear_prefix instead

Remove all values under k1 in the overlay and up to limit in the backend.

All values in the client overlay will be deleted, if there is some limit then up to limit values are deleted from the client backend, if limit is none then all values in the client backend are deleted.

Note

Calling this multiple times per block with a limit set leads always to the same keys being removed and the same result being returned. This happens because the keys to delete in the overlay are not taken into account when deleting keys in the backend.

pub fn clear_prefix<KArg1>( first_key: KArg1, limit: u32, maybe_cursor: Option<&[u8]>, ) -> MultiRemovalResults

where KArg1: ?Sized + EncodeLike<Key1>,

Attempt to remove items from the map matching a first_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 first_key. 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 and first_key. Subsequent calls operating on the same map/first_key should always pass Some, and this should be equal to the previous call result’s maybe_cursor field.

pub fn iter_prefix_values<KArg1>(k1: KArg1) -> PrefixIterator<Value>

where KArg1: ?Sized + EncodeLike<Key1>,

Iterate over values that share the first key.

pub fn mutate<KArg1, KArg2, R, F>(k1: KArg1, k2: KArg2, f: F) -> R

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>, F: FnOnce(&mut QueryKind::Query) -> R,

Mutate the value under the given keys.

pub fn try_mutate<KArg1, KArg2, R, E, F>( k1: KArg1, k2: KArg2, f: F, ) -> Result<R, E>

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>, F: FnOnce(&mut QueryKind::Query) -> Result<R, E>,

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

pub fn mutate_exists<KArg1, KArg2, R, F>(k1: KArg1, k2: KArg2, f: F) -> R

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>, 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<KArg1, KArg2, R, E, F>( k1: KArg1, k2: KArg2, f: F, ) -> Result<R, E>

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>, 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, KArg1, KArg2>( k1: KArg1, k2: KArg2, item: EncodeLikeItem, )

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>, 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<KArg1, KArg2>(key1: KArg1, key2: KArg2) -> Option<usize>

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>, 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 decode_non_dedup_len<KArg1, KArg2>( key1: KArg1, key2: KArg2, ) -> Option<usize>

where KArg1: EncodeLike<Key1>, KArg2: EncodeLike<Key2>, Value: StorageDecodeNonDedupLength,

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

Value is required to implement StorageDecodeNonDedupLength.

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.

• The value returned is the non-deduplicated length of the underlying Vector in storage.This means that any duplicate items are included.

pub fn migrate_keys<OldHasher1: StorageHasher, OldHasher2: StorageHasher, KeyArg1: EncodeLike<Key1>, KeyArg2: EncodeLike<Key2>>( key1: KeyArg1, key2: KeyArg2, ) -> Option<Value>

Migrate an item with the given key1 and key2 from defunct OldHasher1 and OldHasher2 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 remove_all(limit: Option<u32>) -> KillStorageResult

👎Deprecated: Use clear instead

Remove all values in the overlay and up to limit in the backend.

All values in the client overlay will be deleted, if there is some limit then up to limit values are deleted from the client backend, if limit is none then all values in the client backend are deleted.

Note

Calling this multiple times per block with a limit set leads always to the same keys being removed and the same result being returned. This happens because the keys to delete in the overlay are not taken into account when deleting keys in the backend.

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 try_append<KArg1, KArg2, Item, EncodeLikeItem>( key1: KArg1, key2: KArg2, item: EncodeLikeItem, ) -> Result<(), ()>

where KArg1: EncodeLike<Key1> + Clone, KArg2: EncodeLike<Key2> + 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.

impl<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues> StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: StorageInstance, Hasher1: StorageHasher + ReversibleStorageHasher, Hasher2: StorageHasher + ReversibleStorageHasher, Key1: FullCodec, Key2: FullCodec, Value: FullCodec, QueryKind: QueryKindTrait<Value, OnEmpty>, OnEmpty: Get<QueryKind::Query> + 'static, MaxValues: Get<Option<u32>>,

pub fn iter_prefix(k1: impl EncodeLike<Key1>) -> PrefixIterator<(Key2, Value)>

Enumerate all elements in the map with first key k1 in no particular order.

If you add or remove values whose first key is k1 to the map while doing this, you’ll get undefined results.

pub fn iter_prefix_from( k1: impl EncodeLike<Key1>, starting_raw_key: Vec<u8>, ) -> PrefixIterator<(Key2, Value)>

Enumerate all elements in the map with first key k1 after a specified starting_raw_key in no particular order.

If you add or remove values whose first key is k1 to the map while doing this, you’ll get undefined results.

pub fn iter_key_prefix(k1: impl EncodeLike<Key1>) -> KeyPrefixIterator<Key2>

Enumerate all second keys k2 in the map with the same first key k1 in no particular order.

If you add or remove values whose first key is k1 to the map while doing this, you’ll get undefined results.

pub fn iter_key_prefix_from( k1: impl EncodeLike<Key1>, starting_raw_key: Vec<u8>, ) -> KeyPrefixIterator<Key2>

Enumerate all second keys k2 in the map with the same first key k1 after a specified starting_raw_key in no particular order.

If you add or remove values whose first key is k1 to the map while doing this, you’ll get undefined results.

pub fn drain_prefix(k1: impl EncodeLike<Key1>) -> PrefixIterator<(Key2, Value)>

Remove all elements from the map with first key k1 and iterate through them in no particular order.

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

pub fn iter() -> PrefixIterator<(Key1, Key2, Value)>

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<(Key1, Key2, Value)>

Enumerate all elements 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 iter_keys() -> KeyPrefixIterator<(Key1, Key2)>

Enumerate all keys k1 and k2 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<(Key1, Key2)>

Enumerate all keys k1 and k2 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<(Key1, Key2, Value)>

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(Key1, Key2, 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, Hasher1, Hasher2, Key1, Key2, Value, QueryKind, OnEmpty, MaxValues> PartialStorageInfoTrait for StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: StorageInstance, Hasher1: StorageHasher, Hasher2: StorageHasher, Key1: FullCodec, Key2: 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, Hasher1, Hasher2, Key1, Key2, Value, QueryKind, OnEmpty, MaxValues> StorageEntryMetadataBuilder for StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: StorageInstance, Hasher1: StorageHasher, Hasher2: StorageHasher, Key1: FullCodec + StaticTypeInfo, Key2: FullCodec + StaticTypeInfo, 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, Hasher1, Hasher2, Key1, Key2, Value, QueryKind, OnEmpty, MaxValues> StorageInfoTrait for StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: StorageInstance, Hasher1: StorageHasher, Hasher2: StorageHasher, Key1: FullCodec + MaxEncodedLen, Key2: FullCodec + MaxEncodedLen, Value: FullCodec + MaxEncodedLen, QueryKind: QueryKindTrait<Value, OnEmpty>, OnEmpty: Get<QueryKind::Query> + 'static, MaxValues: Get<Option<u32>>,

fn storage_info() -> Vec<StorageInfo>

impl<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues> StoragePrefixedMap<Value> for StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: StorageInstance, Hasher1: StorageHasher, Hasher2: StorageHasher, Key1: FullCodec, Key2: FullCodec, Value: FullCodec, QueryKind: QueryKindTrait<Value, OnEmpty>, OnEmpty: Get<QueryKind::Query> + 'static, MaxValues: Get<Option<u32>>,

fn pallet_prefix() -> &'static [u8]

Pallet prefix. Used for generating final key.

fn storage_prefix() -> &'static [u8]

Storage prefix. Used for generating final key.

fn final_prefix() -> [u8; 32]

Final full prefix that prefixes all keys.

fn remove_all(limit: Option<u32>) -> KillStorageResult

👎Deprecated: Use clear instead

Remove all values in the overlay and up to limit in the backend.

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

Attempt to remove all items from the map.

fn iter_values() -> PrefixIterator<Value>

Iter over all value of the storage.

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.

impl<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues> TryDecodeEntireStorage for StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty, MaxValues>

where Prefix: StorageInstance, Hasher1: StorageHasher, Key1: FullCodec, Hasher2: StorageHasher, Key2: FullCodec, 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.