Struct Mapping

pub struct Mapping<K, V: Packed, KeyType: StorageKey = AutoKey> { /* private fields */ }

A mapping of key-value pairs directly into contract storage.

Important

The mapping requires its own pre-defined storage key where to store values. By default, the key is automatically calculated using AutoKey during compilation. However, anyone can specify a storage key using ManualKey. Specifying the storage key can be helpful for upgradeable contracts or you want to be resistant to future changes of storage key calculation strategy.

This is an example of how you can do this:

use ink::{
    U256,
    storage::{
        Mapping,
        traits::ManualKey,
    },
};

#[ink(storage)]
#[derive(Default)]
pub struct MyContract {
    balances: Mapping<Address, U256, ManualKey<123>>,
}

impl MyContract {
    #[ink(constructor)]
    pub fn new() -> Self {
        let mut instance = Self::default();
        let caller = Self::env().caller();
        let value: U256 = Default::default();
        instance.balances.insert(&caller, &value);
        instance
    }

}

More usage examples can be found in the ink! examples.

Implementations

impl<K, V, KeyType> Mapping<K, V, KeyType>

where V: Packed, KeyType: StorageKey,

pub const fn new() -> Self

Creates a new empty Mapping.

impl<K, V, KeyType> Mapping<K, V, KeyType>

where K: Encode, V: Packed, KeyType: StorageKey,

pub fn insert<Q, R>(&mut self, key: Q, value: &R) -> Option<u32>

where Q: EncodeLike<K>, R: Storable + EncodeLike<V>,

Insert the given value to the contract storage.

Returns the size in bytes of the pre-existing value at the specified key if any.

Panics

Traps if encoding the key together with the value doesn’t fit into the static buffer.

pub fn try_insert<Q, R>(&mut self, key: Q, value: &R) -> Result<Option<u32>>

where Q: EncodeLike<K>, R: Storable + EncodeLike<V>,

Try to insert the given value into the mapping under given key.

Fails if key or value exceeds the static buffer size.

Returns:

• Ok(Some(_)) if the value was inserted successfully, containing the size in bytes of the pre-existing value at the specified key if any.
• Ok(None) if the insert was successful but there was no pre-existing value.
• Err(_) if encoding the key together with the value exceeds the static buffer size.

pub fn get<Q>(&self, key: Q) -> Option<V>

where Q: EncodeLike<K>,

Get the value at key from the contract storage.

Returns None if no value exists at the given key.

Panics

Traps if the encoded key or value doesn’t fit into the static buffer.

pub fn try_get<Q>(&self, key: Q) -> Option<Result<V>>

where Q: EncodeLike<K>,

Try to get the value at the given key.

Returns:

• Some(Ok(_)) containing the value if it existed and was decoded successfully.
• Some(Err(_)) if either (a) the encoded key doesn’t fit into the static buffer or (b) the value existed but its length exceeds the static buffer size.
• None if there was no value under this mapping key.

pub fn take<Q>(&self, key: Q) -> Option<V>

where Q: EncodeLike<K>,

Removes the value at key, returning the previous value at key from storage.

Returns None if no value exists at the given key.

Panics

Traps if the encoded key or value doesn’t fit into the static buffer.

pub fn try_take<Q>(&self, key: Q) -> Option<Result<V>>

where Q: EncodeLike<K>,

Try to take the value at the given key. On success, this operation will remove the value from the mapping

Returns:

• Some(Ok(_)) containing the value if it existed and was decoded successfully.
• Some(Err(_)) if either (a) the encoded key doesn’t fit into the static buffer or (b) the value existed but its length exceeds the static buffer size.
• None if there was no value under this mapping key.

pub fn size<Q>(&self, key: Q) -> Option<u32>

where Q: EncodeLike<K>,

Get the size in bytes of a value stored at key in the contract storage.

Returns None if no value exists at the given key.

pub fn contains<Q>(&self, key: Q) -> bool

where Q: EncodeLike<K>,

Checks if a value is stored at the given key in the contract storage.

Returns false if no value exists at the given key.

pub fn remove<Q>(&self, key: Q)

where Q: EncodeLike<K>,

Clears the value at key from storage.

Trait Implementations

impl<K, V, KeyType> Debug for Mapping<K, V, KeyType>

where V: Packed, KeyType: StorageKey,

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<K, V, KeyType> Default for Mapping<K, V, KeyType>

where V: Packed, KeyType: StorageKey,

We implement this manually because the derived implementation adds trait bounds.

fn default() -> Self

Returns the “default value” for a type.

impl<K, V, KeyType> Storable for Mapping<K, V, KeyType>

where V: Packed, KeyType: StorageKey,

fn encode<T: Output + ?Sized>(&self, _dest: &mut T)

Convert self to a slice and append it to the destination.

fn decode<I: Input>(_input: &mut I) -> Result<Self, Error>

Attempt to deserialize the value from input.

fn encoded_size(&self) -> usize

The exact number of bytes this type consumes in the encoded form.

impl<K, V, Key, InnerKey> StorableHint<Key> for Mapping<K, V, InnerKey>

where V: Packed, Key: StorageKey, InnerKey: StorageKey,

type Type = Mapping<K, V, Key>

Storable type with storage key inside.

type PreferredKey = InnerKey

The storage key that the type prefers. It can be overwritten by an auto-generated storage key.

impl<K, V, KeyType> StorageKey for Mapping<K, V, KeyType>

where V: Packed, KeyType: StorageKey,

const KEY: Key = KeyType::KEY

Storage key of the type.

fn key(&self) -> u32

Returns the storage key.

impl<K, V, KeyType> StorageLayout for Mapping<K, V, KeyType>

where K: TypeInfo + 'static, V: Packed + StorageLayout + TypeInfo + 'static, KeyType: StorageKey + TypeInfo + 'static,

fn layout(_: &Key) -> Layout

Returns the static storage layout of Self.

impl<K, V, KeyType> TypeInfo for Mapping<K, V, KeyType>

where PhantomData<fn() -> (K, V, KeyType)>: TypeInfo + 'static, K: TypeInfo + 'static, V: Packed + TypeInfo + 'static, KeyType: StorageKey + TypeInfo + 'static,

type Identity = Mapping<K, V, KeyType>

The type identifying for which type info is provided.

fn type_info() -> Type

Returns the static type identifier for Self.