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URL: https://dev.to/abdulsalamamtech/step-by-step-crud-operation-in-motoko-how-to-store-and-retrieve-data-34fp

⇱ step by step crud operation in motoko - how to store and retrieve data - DEV Community

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.

  1. 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
};
  1. 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.

Run and test

# Starts the replica, running in the background
dfx start --background

# Deploys your canisters to the replica and generates your candid interface. It basically deploys the fullstack application

dfx deploy

Read more...
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