To store 1 question and 4 options in Motoko efficiently, you should define a structured Record type to hold the data, rather than a raw Buffer. If you need to store multiple of these questions in a resizable container, you would use a Buffer to hold those records.
Here is the recommended implementation using an Actor to manage the question storage.
- Define the TypesUse a stable Record type to ensure the data persists across upgrades.
motoko
type Option = Text;
type Question = {
questionText : Text;
options : [Option]; // Array of 4 options
correctOptionIndex : Nat; // Index 0-3
};
- Implementation Using BufferThis actor initializes with a Buffer to store multiple Question records.
motoko
import Buffer "mo:base/Buffer";
import Array "mo:base/Array";
actor QuestionManager {
// Define the type for the question
public type Question = {
questionText : Text;
options : [Text]; // Expected size 4
correctOptionIndex : Nat; // 0, 1, 2, or 3
};
// Buffer is a resizable array
let questionsBuffer = Buffer.Buffer<Question>(10);
// Function to add a question
public func addQuestion(q : Question) : async () {
// Simple validation: Ensure 4 options
if (q.options.size() == 4) {
questionsBuffer.add(q);
};
};
// Function to get all questions
public query func getQuestions() : async [Question] {
// Convert buffer to immutable array for returning
return questionsBuffer.toArray();
};
// Function to get total question count
public query func getCount() : async Nat {
return questionsBuffer.size(); //
};
}
Key Motoko Concepts
Used[Records]: { questionText : Text; ... } defines a structured object.
[Buffer]: Buffer.Buffer(10) creates a mutable, resizable container, ideal for managing lists of data on the heap.
[Array]: [Text] is a fixed-size array, perfect for the 4 options, ensuring they are immutable and easily shared.
ToArray: questionsBuffer.toArray() converts the mutable buffer into a shared, immutable array format required for canister return values.
Read more...
Motoko Book
Mops Docs