blockchain-interactions.md

description
description: Query and mutate Flow blockchain

Blockchain Interactions

{% hint style="warning" %} Make sure you have set the configuration in Getting Started first. {% endhint %}

We are assuming you have read the Scripts Documentation before this, as transactions are sort of scripts with more required things.

There are two different operations to interact with Flow blockchain:

1. Query: Send arbitrary Cadence scripts to the chain and receive ExecuteResult<ICadence> values. Can be performed without user login
2. Mutate: Use transaction to send Cadence code with specify authorizer to perform permanently state changes on chain. Must be performed after user logged in

about ICadance, you can get more detailed description from Flow.Net

Query

using Flow.FCL;
using Flow.Net.Sdk.Core.Models;

var script = @" 
            pub struct User {
                pub var balance: UFix64
                pub var address: Address
                pub var name: String
                
                init(name: String, address: Address, balance: UFix64) {
                    self.name = name
                    self.address = address
                    self.balance = balance
                }
            }

            pub fun main(name: String): User {
                return User(
                    name: name,
                    address: 0x1,
                    balance: 10.0
                )
            }";

var flowScript = new FlowScript
                    {
                        Script = script,
                        Arguments = new List<ICadence>
                                    {
                                        new CadenceString("blocto")
                                    }
                    };

var result = await fcl.QueryAsync(flowScript);
if(result.IsSuccessed)
{
    //// Composite object parser
    var name = result.Data.As<CadenceComposite>().CompositeFieldAs<CadenceString>("name").Value;
    var balance = result.Data.As<CadenceComposite>().CompositeFieldAs<CadenceNumber>("balance").Value;
    var address = result.Data.As<CadenceComposite>().CompositeFieldAs<CadenceAddress>("address").Value;
    Debug.Log($"Name: {name}, Balance: {balance}, Address: {address})";
}
else
{
    Debug.Log($"Error message: {result.Message}");
}

Mutate

using Flow.FCL;
using Flow.Net.Sdk.Core.Models;

var script = @"
            import ValueDapp from 0x5a8143da8058740c

            transaction(value: UFix64) {
                prepare(authorizer: AuthAccount) {
                    ValueDapp.setValue(value)
                }
            }";

var tx = new FlowTransaction
            {
                Script = script,
                GasLimit = 1000,
                Arguments = new List<ICadence>
                            {
                                new CadenceNumber(CadenceNumberType.UFix64, "123.456"),
                            },
            };

fcl.Mutate(
    tx: tx,
    callback: txId => {
                   Debug.Log($"https://testnet.flowscan.org/transaction/{txId}");
               });

While query is used for sending scripts to the chain, mutate is used for building and sending transactions.

Transaction status

In order to check transaction status, we can use getTransactionStatus in fcl to keep polling until transaction have been sealed into block.

var result = _fcl.GetTransactionStatus(_txId);
if(result.IsSuccessed)
{
    switch (result.Data.Execution)
    {
        case TransactionExecution.Failure:
            Debug.Log($"Execution: Failure \r\nErrorMessage: {result.Message}");
            break;
        case TransactionExecution.Success:
            Debug.Log($"BlockId: {result.Data.BlockId} \r\nExecution: {result.Data.Execution} \r\nStatus: {result.Data.Status}");
            break;
        case TransactionExecution.Pending:
            Debug.Log($"{result.Message}");
            break;
    }
}

After the status changes to sealed, we can query the Flow blockchain to see if the transaction works as expected.