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

A type that allow to store value for given key. Allowing to insert/remove/iterate on values.

Each value is stored at:

Twox128(Prefix::pallet_prefix())
		++ Twox128(Prefix::STORAGE_PREFIX)
		++ Hasher1(encode(key))

Warning

If the keys are not trusted (e.g. can be set by a user), a cryptographic hasher such as blake2_128_concat must be used. Otherwise, other values in storage can be compromised.

Implementations

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

Does the value (explicitly) exist in storage?

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

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

Returns Ok if it exists, Err if not.

Swap the values of two keys.

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

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

Remove the value under a key.

Mutate the value under a key.

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

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

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.

Take the value under a key.

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.

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.

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.

👎Deprecated: Use clear instead

Remove all values of the storage 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.

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.

Iter over all value of the storage.

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

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.

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

Is only available if Value of the storage implements StorageTryAppend.

Enumerate all elements in the map in no particular order.

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

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

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

Enumerate all keys in the map in no particular order.

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

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

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

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.

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

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

Build into entries the storage metadata entries of a storage given some docs.
Module prefix. Used for generating final key.
Storage prefix. Used for generating final key.
Final full prefix that prefixes all keys.
👎Deprecated: Use clear instead
Remove all values in the overlay and up to limit in the backend. Read more
Attempt to remove all items from the map. Read more
Iter over all value of the storage. Read more
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. Read more

Auto Trait Implementations

Blanket Implementations

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Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

Get a reference to the inner from the outer.

Get a mutable reference to the inner from the outer.

The alignment of pointer.
The type for initializers.
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Should always be Self
Convert from a value of T into an equivalent instance of Self. Read more
Consume self to return an equivalent value of T. Read more
The type that get/take return.
Get the storage key used to fetch a value corresponding to a specific key.
Swap the values of two keys.
Does the value (explicitly) exist in storage?
Load the value associated with the given key from the map.
Try to get the value for the given key from the map. Read more
Store or remove the value to be associated with key so that get returns the query.
Store a value to be associated with the given key from the map.
Remove the value under a key.
Mutate the value under a key.
Mutate the value under a key. Read more
Mutate the item, only if an Ok value is returned.
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. Read more
Take the value under a key.
Append the given items to the value in the storage. Read more
Migrate an item with the given key from a defunct OldHasher to the current hasher. Read more
Read the length of the storage value without decoding the entire value under the given key. Read more
Migrate an item with the given key from a blake2_256 hasher to the current hasher. Read more
Try and append the item into the storage map at the given key. Read more
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Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.
The counterpart to unchecked_from.
Consume self to return an equivalent value of T.
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