Trait frame_support::storage::StoragePrefixedMap
source · pub trait StoragePrefixedMap<Value: FullCodec> {
// Required methods
fn module_prefix() -> &'static [u8] ⓘ;
fn storage_prefix() -> &'static [u8] ⓘ;
// Provided methods
fn final_prefix() -> [u8; 32] { ... }
fn remove_all(limit: Option<u32>) -> KillStorageResult { ... }
fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> MultiRemovalResults { ... }
fn iter_values() -> PrefixIterator<Value> ⓘ { ... }
fn translate_values<OldValue: Decode, F: FnMut(OldValue) -> Option<Value>>(
f: F
) { ... }
}Expand description
Trait for maps that store all its value after a unique prefix.
By default the final prefix is:
Twox128(module_prefix) ++ Twox128(storage_prefix)
Required Methods§
sourcefn module_prefix() -> &'static [u8] ⓘ
fn module_prefix() -> &'static [u8] ⓘ
Module prefix. Used for generating final key.
sourcefn storage_prefix() -> &'static [u8] ⓘ
fn storage_prefix() -> &'static [u8] ⓘ
Storage prefix. Used for generating final key.
Provided Methods§
sourcefn final_prefix() -> [u8; 32]
fn final_prefix() -> [u8; 32]
Final full prefix that prefixes all keys.
sourcefn remove_all(limit: Option<u32>) -> KillStorageResult
fn remove_all(limit: Option<u32>) -> KillStorageResult
clear insteadRemove 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.
sourcefn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> MultiRemovalResults
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.
sourcefn iter_values() -> PrefixIterator<Value> ⓘ
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.
sourcefn translate_values<OldValue: Decode, F: FnMut(OldValue) -> Option<Value>>(f: F)
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.