PersistentMap

This class is one of several convenience collections built on top of the Storage class It implements a map -- a persistent unordered map.

To create a map

let map = new PersistentMap<string, string>("m")  // choose a unique prefix per account

To use the map

map.set(key, value)
map.get(key)

IMPORTANT NOTES:

(1) The Map doesn't store keys, so if you need to retrieve them, include keys in the values.

(2) Since all data stored on the blockchain is kept in a single key-value store under the contract account, you must always use a unique storage prefix for different collections to avoid data collision.

Type parameters

Name	Description
K	The generic type parameter K can be any valid AssemblyScript type.
V	The generic type parameter V can be any valid AssemblyScript type. MISC: Original code from Near (https://github.com/near/near-sdk-as/blob/master/sdk-core/assembly/collections/persistentMap.ts)

Hierarchy

• PersistentMap

  ↳ Oracle

Table of contents

Constructors

• constructor

Properties

• _elementPrefix
• _size

Methods

• _decreaseSize
• _increaseSize
• _key
• contains
• delete
• get
• getSome
• set
• size

Constructors

constructor

• new PersistentMap<K, V>(prefix): PersistentMap<K, V>

Creates or restores a persistent map with a given storage prefix. Always use a unique storage prefix for different collections.

Example

let map = new PersistentMap<string, string>("m") // note the prefix must be unique (per MASSA account)

Type parameters

Name
K
V

Parameters

Name	Type	Description
prefix	string	A prefix to use for every key of this map.

Returns

PersistentMap<K, V>

Defined in

assembly/libraries/PersistentMap.ts:65

Properties

_elementPrefix

• Private _elementPrefix: string

Defined in

assembly/libraries/PersistentMap.ts:51

---

_size

• Private _size: usize

Defined in

assembly/libraries/PersistentMap.ts:52

Methods

_decreaseSize

▸ _decreaseSize(): void

Decreases the internal map size counter

Returns

void

Defined in

assembly/libraries/PersistentMap.ts:144

---

_increaseSize

▸ _increaseSize(key): void

Increases the internal map size counter

Parameters

Name	Type	Description
key	K	Key to remove.

Returns

void

Defined in

assembly/libraries/PersistentMap.ts:135

---

_key

▸ _key(key): StaticArray<u8>

Parameters

Name	Type	Description
key	K	Search key.

Returns

StaticArray<u8>

An internal string key for a given key of type K.

Defined in

assembly/libraries/PersistentMap.ts:74

---

contains

▸ contains(key): bool

Checks whether the map contains a given key

let map = new PersistentMap<string, string>("m")

map.contains("hello")      // false
map.set("hello", "world")
map.contains("hello")      // true

Parameters

Name	Type	Description
key	K	Key to check.

Returns

bool

True if the given key present in the map.

Defined in

assembly/libraries/PersistentMap.ts:94

---

delete

▸ delete(key): void

Removes the given key and related value from the map

let map = new PersistentMap<string, string>("m")

map.set("hello", "world")
map.delete("hello")

Removes value and the key from the map.

Parameters

Name	Type	Description
key	K	Key to remove.

Returns

void

Defined in

assembly/libraries/PersistentMap.ts:126

---

get

▸ get(key, defaultValue): V

Retrieves the related value for a given key, or uses the defaultValue if not key is found

let map = new PersistentMap<string, string>("m")

map.set("hello", "world")
let found = map.get("hello")
let notFound = map.get("goodbye", "cruel world")

assert(found == "world")
assert(notFound == "cruel world")

Parameters

Name	Type	Description
key	K	Key of the element.
defaultValue	V	The default value if the key is not present.

Returns

V

Value for the given key or the default value.

Defined in

assembly/libraries/PersistentMap.ts:168

---

getSome

▸ getSome(key, msg?): V

Retrieves a related value for a given key or fails assertion with "key not found"

let map = new PersistentMap<string, string>("m")

map.set("hello", "world")
let result = map.getSome("hello")
// map.getSome("goodbye")  // will throw with failed assertion

assert(result == "world")

Parameters

Name	Type	Default value	Description
key	K	undefined	Key of the element.
msg	string	'key not found'	-

Returns

V

Value for the given key or the default value.

Defined in

assembly/libraries/PersistentMap.ts:230

---

set

▸ set(key, value): void

let map = new PersistentMap<string, string>("m")

map.set("hello", "world")

Sets the new value for the given key.

Parameters

Name	Type	Description
key	K	Key of the element.
value	V	The new value of the element.

Returns

void

Defined in

assembly/libraries/PersistentMap.ts:273

---

size

▸ size(): usize

Returns the map size

Returns

usize

the map size

Example

let map = new PersistentMap<string, string> ("m")

map.size()

Defined in

assembly/libraries/PersistentMap.ts:109