classlib/ExpenseTracker.Application/Transactions/Queries/Get/GetTransactionQueryHandler.cs

using AutoMapper;
using MediatR;
using ExpenseTracker.Application.Common.Interfaces.Repositories;
using ExpenseTracker.Domain.Entities;

namespace ExpenseTracker.Application.Transactions.Queries.Get;

public class GetTransactionQueryHandler : IRequestHandler<GetTransactionQuery, TransactionDto>
{
    private readonly IMapper _mapper;
    private readonly ITransactionRepository _transactionRepository;
    private readonly IAccountRepository _accountRepository;

    public GetTransactionQueryHandler(
        IMapper mapper,
        ITransactionRepository repository,
        IAccountRepository accountRepository)
    {
        _mapper = mapper;
        _transactionRepository = repository;
        _accountRepository = accountRepository;
    }

    public async Task<TransactionDto> Handle(GetTransactionQuery request, CancellationToken cancellationToken)
    {
        var entity = _transactionRepository.Queryable
            .Join(
                _accountRepository.Queryable,
                t => t.AccountId,
                b => b.Id,
                (transaction, account) =>
                    new Transaction
                    {
                        Id = transaction.Id,
                        Amount = transaction.Amount,
                        Category = transaction.Category,
                        Time = transaction.Time,
                        Description = transaction.Description,
                        Account = account,
                        AccountId = transaction.AccountId
                    }
            )
            .FirstOrDefault(e => e.Id == request.Id);

        return _mapper.Map<TransactionDto>(entity);
    }
}