Struct frame_support::pallet_prelude::StorageDoubleMap

pub struct StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind = OptionQuery, OnEmpty = GetDefault>(_);

A type that allow to store values for (key1, key2) couple. Similar to StorageMap but allow to iterate and remove value associated to first key.

Each value is stored at:

Twox128(Prefix::pallet_prefix())
	++ Twox128(Prefix::STORAGE_PREFIX)
	++ Hasher1(encode(key1))
	++ Hasher2(encode(key2))

Warning

If the key1s (or key2s) are not trusted (e.g. can be set by a user), a cryptographic hasher such as blake2_128_concat must be used for Hasher1 (resp. Hasher2). Otherwise, other values in storage can be compromised.

Implementations

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

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 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) where
    KArg1: ?Sized + EncodeLike<Key1>, 

Remove all values under the first key.

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.

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 completly ignored by this function.

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()

Remove all value of the storage.

pub fn iter_values() -> PrefixIterator<Value>

Iter over all value of the storage.

NOTE: If a value failed to decode becaues 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.

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

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 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 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> StorageDoubleMapMetadata for StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty> where
    Prefix: StorageInstance,
    Hasher1: StorageHasher,
    Hasher2: StorageHasher,
    Key1: FullCodec,
    Key2: FullCodec,
    Value: FullCodec,
    QueryKind: QueryKindTrait<Value, OnEmpty>,
    OnEmpty: Get<QueryKind::Query> + 'static, 

const MODIFIER: StorageEntryModifier

const HASHER1: StorageHasher

const HASHER2: StorageHasher

const NAME: &'static str

const DEFAULT: DefaultByteGetter

impl<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty> StoragePrefixedMap<Value> for StorageDoubleMap<Prefix, Hasher1, Key1, Hasher2, Key2, Value, QueryKind, OnEmpty> where
    Prefix: StorageInstance,
    Hasher1: StorageHasher,
    Hasher2: StorageHasher,
    Key1: FullCodec,
    Key2: FullCodec,
    Value: FullCodec,
    QueryKind: QueryKindTrait<Value, OnEmpty>,
    OnEmpty: Get<QueryKind::Query> + 'static, 

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

Module 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()

Remove all value of the storage.

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.