Skip to main content

Data Storage / Collections

Overview

All data stored on the NEAR blockchain is done in key / value pairs. There are several collection methods in the SDKs we've created that will help you store your data on chain.

For information on storage costs, please see [ storage staking ].


AssemblyScript Collection Types

near-sdk-as

TypeIterableClear All ValuesPreserves Insertion OrderRange Selection
PersistentVector
PersistentSet
PersistentMap
PersistentUnorderedMap
PersistentDeque
AVLTree

Big-O Notation

The Big-O notation values in the chart below describe the time complexity of the various collection methods found in near-sdk-as. These method complexities correlate with gas consumption on NEAR, helping you decide which collection to utilize in your project. There are three types found in our collection methods:

TypeAccessInsertDeleteSearchTraverseClear
PersistentVectorO(1)O(1)*O(1)**O(n)O(n)O(n)
PersistentSetO(1)O(1)O(1)O(1)O(n)O(n)
PersistentMapO(1)O(1)O(1)O(1)N/AN/A
PersistentUnorderedMapO(1)O(1)O(1)O(1)O(n)O(n)
PersistentDequeO(1)O(1)*O(1)**O(1)O(n)O(n)
AVLTreeO(log n)O(log n)O(log n)O(log n)O(n)O(n)

* - to insert at the end of the vector using push_back (or push_front for deque)

** - to delete from the end of the vector using pop (or pop_front for deque), or delete using swap_remove which swaps the element with the last element of the vector and then removes it.


Gas Consumption Examples

The examples below show differences in gas burnt storing and retrieving key/value pairs using the above methods. Please note that the gas cost of spinning up the runtime environment on chain has been deducted to show just data read/writes.

You can reproduce this and test out your own data set by visiting collection-examples-as.

AssemblyScript Set Data Gas Chart

AssemblyScript Get Data Gas Chart


PersistentVector

Implements a vector / persistent array built on top of the Storage class.

Uses the following map: index -> element.

  • To create:
import { PersistentVector } from "near-sdk-as";
let vector = new PersistentVector<string>("v"); // choose a unique prefix per collection
  • To use:
vector.push(value);
vector.pop(value);
vector.length;

[ SDK source ]


PersistentSet

Built on top of the Storage class, this implements a persistent set without iterators.

  • is not iterable
  • more efficient in the number of reads and writes

[ SDK source ]


PersistentMap

Implements a map built on top of the Storage.

  • To create:
import { PersistentMap } from "near-sdk-as";
let map = new PersistentMap<string, string>("pmap"); // choose a unique prefix per collection
  • To use:
map.set(key, value);
map.getSome(key);

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

[ SDK source ]


PersistentUnorderedMap

Implements an unordered map built on top of the PersistentMap class and a PersistentVector, which stores the keys of the map. These keys are initially in the order they are inserted, however, a deleted key is swapped with the last key.

  • To create:
import { PersistentUnorderedMap } from "near-sdk-as";
let map = new PersistentUnorderedMap<string, string>("umap"); // note the prefix must be unique per collection
  • To use:
map.set(key, value);
map.getSome(key);

[ SDK source ]


PersistentDeque

Built on top of the Storage class, this implements a persistent bidirectional queue / double-ended queue / deque.

  • To create:
import { PersistentDeque } from "near-sdk-as";
let dq = new PersistentDeque<string>("deque"); // choose a unique prefix per collection
  • To use:
dq.pushFront(value);
dq.popBack();

[ SDK source ]


AVLTree

Implements a Tree Map based on AVL-tree Keys are ordered and iterable.

  • To create:
import { AVLTree } from "near-sdk-as";
map = new AVLTree<string, string>("avl"); // choose a unique prefix per account
  • To use:
map.set(key, value);
map.getSome(key)

[ SDK source ]


Rust Collection Types

near-sdk-rs module documentation

TypeIterableClear All ValuesPreserves Insertion OrderRange Selection
Vector
LookupSet
UnorderedSet
LookupMap
UnorderedMap
TreeMap

Big-O Notation

The Big-O notation values in the chart below describe the time complexity of the various collection methods found in near-sdk-rs. These method complexities correlate with gas consumption on NEAR, helping you decide which collection to utilize in your project. There are three types found in our collection methods:

TypeAccessInsertDeleteSearchTraverseClear
VectorO(1)O(1)*O(1)**O(n)O(n)O(n)
LookupSetO(1)O(1)O(1)O(1)N/AN/A
UnorderedSetO(1)O(1)O(1)O(1)O(n)O(n)
LookupMapO(1)O(1)O(1)O(1)N/AN/A
UnorderedMapO(1)O(1)O(1)O(1)O(n)O(n)
TreeMapO(log n)O(log n)O(log n)O(log n)O(n)O(n)

* - to insert at the end of the vector using push_back (or push_front for deque)

** - to delete from the end of the vector using pop (or pop_front for deque), or delete using swap_remove which swaps the element with the last element of the vector and then removes it.


Gas Consumption Examples

The examples below show differences in gas burnt storing and retrieving key/value pairs using the above methods. Please note that the gas cost of spinning up the runtime environment on chain has been deducted to show just data read/writes.

You can reproduce this and test out your own data set by visiting collection-examples-rs.

Rust Set Data Gas Chart

Rust Get Data Gas Chart


Vector

Implements a vector / persistent array.

  • can iterate using index
  • Uses the following map: index -> element.

[ SDK source ]

[ Implementation ]


LookupSet

Implements a persistent set without iterators.

  • can not iterate over keys
  • more efficient in reads / writes

[ SDK source ]

[ Implementation ]


UnorderedSet

Implements a persistent set with iterators for keys, values, and entries.

[ SDK source ]

[ Implementation Docs ]


LookupMap

Implements a persistent map.

  • can not iterate over keys
  • does not preserve order when removing and adding values
  • efficient in number of reads and writes
  • To add data:
pub fn add_lookup_map(&mut self, key: String, value: String) {
self.lookup_map.insert(&key, &value);
}
  • To get data:
pub fn get_lookup_map(&self, key: String) -> String {
match self.lookup_map.get(&key) {
Some(value) => {
let log_message = format!("Value from LookupMap is {:?}", value.clone());
env::log(log_message.as_bytes());
value
},
None => "not found".to_string()
}
}

[ SDK source ]

[ Implementation ]


UnorderedMap

Implements an unordered map.

  • iterable
  • does not preserve order when removing and adding values
  • is able to clear all values
  • To add data:
pub fn add_unordered_map(&mut self, key: String, value: String) {
self.unordered_map.insert(&key, &value);
}
  • To get data:
pub fn get_unordered_map(&self, key: String) -> String {
match self.unordered_map.get(&key) {
Some(value) => {
let log_message = format!("Value from UnorderedMap is {:?}", value.clone());
env::log(log_message.as_bytes());
value
},
// None => "Didn't find that key.".to_string()
None => "not found".to_string()
}
}

[ SDK source ]

[ Implementation ]


TreeMap

Implements a Tree Map based on AVL-tree.

  • iterable
  • preserves order
  • able to clear all values
  • self balancing
  • To add data:
pub fn add_tree_map(&mut self, key: String, value: String) {
self.tree_map.insert(&key, &value);
}
  • To get data:
pub fn get_tree_map(&self, key: String) -> String {
match self.tree_map.get(&key) {
Some(value) => {
let log_message = format!("Value from TreeMap is {:?}", value.clone());
env::log(log_message.as_bytes());
// Since we found it, return it (note implicit return)
value
},
// did not find the entry
// note: curly brackets after arrow are optional in simple cases, like other languages
None => "not found".to_string()
}
}

[ SDK source ]

[ Implementation ]