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Unit of Work


This page contains the recommended way of implementing a Unit of Work (UOW) object when using this library. The consolidated output of this page can be found here.

Interface

Create an inteface that would enable your UOW class to be dependency injectable.

public interface IUnitOfWork<TDbConnection>
{
    TDbConnection Connection { get; }
    DbTransaction Transaction { get ; }
    void Begin();
    void Rollback();
    void Commit();
}

Ensure that this interface is accepting a generic type of the connection object.

Then, save the following properties that will hold the state of transaction.

NameDescription
ConnectionWill hold the instance of the connection object.
TransactionWill hold the instance of the active transaction.

And, create the 3 basic transactional methods.

NameDescription
BeginIs used to begin a new transaction.
CommitIs used to commit an existing transaction.
RollbackIs used to rollback an existing transaction.

Class

Create a class that implements the newly created interface. Here, let us assume we have the AppSettings class as the configuration class.

public class CustomUnitOfWork : IUnitOfWork<SqlConnection>
{
    private AppSettings _appSettings;
    private SqlConnection _connection;
    private DbTransaction _transaction;

    public CustomUnitOfWork(IOptions<AppSettings> options)
    {
        _appSettings = options.Value;
    }

    public SqlConnection Connection => _connection;

    public DbTransaction Transaction => _transaction;

    public void Begin()
    {
        if (_transaction != null)
        {
            throw new InvalidOperationException("Cannot start a new transaction while the existing one is still open.");
        }
        _connection = _connection ??= (new SqlConnection(_appSettings.ConnectionString)).EnsureOpen();
        _transaction = _connection.BeginTransaction();
    }

    public void Commit()
    {
        if (_transaction == null)
        {
            throw new InvalidOperationException("There is no active transaction to commit.");
        }
        using (_transaction)
        {
            _transaction.Commit();
        }
        _transaction = null;
    }

    public void Rollback()
    {
        if (_transaction == null)
        {
            throw new InvalidOperationException("There is no active transaction to rollback.");
        }
        using (_transaction)
        {
            _transaction.Rollback();
        }
        _transaction = null;
    }
}

Please note that the corresponding asynchronous methods were not implemented on this sample. You have to introduce it yourself if you wish to have it covered.

Repositories

First, implement the base interface that contains the necessary methods.

public interface IRepository<TEntity, TDbConnection>
    where TEntity : class
    where TDbConnection : IDbConnection
{
    void Attach(IUnitOfWork<TDbConnection> unitOfWork);
    TResult Save<TResult>(TEntity entity);
    int SaveAll(IEnumerable<TEntity> entities);
    int Delete(object id);
    TResult Merge<TResult>(TEntity entity);
    TEntity Query(object id);
    int Update(TEntity entity);
}

Then, implement the entity level interface repository.

public interface IOrderRepository : IRepository<Order, SqlConnection>
{
    ...
}

public interface IOrderItemRepository : IRepository<OrderItem, SqlConnection>
{
    ...
}

Then, implement a base repository that has the unit-of-work capability. Let us call this repository EntityRepository.

public class EntityRepository<TEntity> : BaseRepository<TEntity, SqlConnection>,
    IRepository<TEntity, SqlConnection>
    where TEntity : class
{
    private IUnitOfWork<SqlConnection> _unitOfWork;

    public EntityRepository(IOptions<AppSettings> options)
        : base(options.Value.ConnectionString) { }

    public void Attach(IUnitOfWork<SqlConnection> unitOfWork) =>
        _unitOfWork = unitOfWork;

    public TResult Save<TResult>(TEntity entity) =>
        Insert<TResult>(entity,
            transaction: _unitOfWork.Transaction);

    public int SaveAll(IEnumerable<TEntity> entities) =>
        InsertAll(entities,
            transaction: _unitOfWork.Transaction);

    public int Delete(object id) =>
        Delete(id,
            transaction: _unitOfWork.Transaction);

    public TResult Merge<TResult>(TEntity entity) =>
        Merge<TResult>(entity,
            transaction: _unitOfWork?.Transaction);

    public TEntity Query(object id) =>
        Query(id,
            transaction: _unitOfWork?.Transaction)?.FirstOrDefault();

    public int Update(TEntity entity) =>
        Update(entity,
            transaction: _unitOfWork?.Transaction);
}

Take note of the method Attach(), it accepts an instance of IUnitOfWork<SqlConnection> object. This method will be used in the business logic to passed the currently injected (in-used) UOW class. Also, the variable _unitOfWork will hold an instance of IUnitOfWork<SqlConnection> interface that has been created when the Attach() method is called.

Then, create a repository class that inherits either the DbRepository or BaseRepository. On this class, implement the newly created I<Entity>Repository interface, the one that implements the IRepository<TEntity, TDbConnection> interface.

public class OrderRepository : EntityRepository<Order>, IOrderRepository
{
    public OrderRepository(IOptions<Settings> options)
        : base(options)
    { }
}

public class OrderItemRepository : EntityRepository<OrderItem>, IOrderItemRepository
{
    public OrderRepository(IOptions<Settings> options)
        : base(options)
    { }
}

Please note that the corresponding asynchronous methods were not implemented on this sample. You have to introduce it yourself if you wish to have it covered.

Dependency Injection

Register the UOW interface and class via service registration. Ensure it is on transient level.

public void ConfigureServices(IServiceCollection services)
{
    services.SaveControllers();

    // Registration
    services.AddTransient<IUnitOfWork<SqlConnection>, CustomUnitOfWork>();
}

Also, register the repositories as singleton.

services.AddSingleton<IOrderRepository, OrderRepository>();
services.AddSingleton<IOrderItemRepository, OrderItemRepository>();
/* Do the same for the other repositories */

Business Logic

In your business logic, make sure that the IUnitOfWork<SqlConnection> is being dependency injected. Let us assumed your business logic class is named SalesManager that implements the ISalesManager interface.

public interface ISalesManager
{
    void SaveOrder(Order order,
        IEnumerable<OrderItem> orderItems);

    /* More business logic methods */
}

public class SalesManager : ISalesManager
{
    private IUnitOfWork<SqlConnection> _unitOfWork;
    private IOrderRepository _orderRepository;
    private IOrderItemRepository _orderItemRepository;

    public SalesManager(IUnitOfWork unitOfWork,
        IOrderRepository orderRepository,
        IOrderItemRepository orderItemRepository,
        /* Other repositories here */)
    {
        _unitOfWork = unitOfWork;
        _orderRepository = orderRepository;
        _orderItemRepository = orderItemRepository;

        // Attach the UOW
        _orderRepository.Attach(_unitOfWork);
        _orderItemRepository.Attach(_unitOfWork);
    }
}

In any of your business logic methods, ensure that you properly call the Begin(), Commit() and Rollback() methods of the _unitOfWork variable.

Below is a sample method that saves the order and its order item.

public void SaveOrders(Order order,
    IEnumerable<OrderItem> orderItems)
{
    // Start the UOW
    _unitOfWork.Begin();

    try
    {
        // Call the repository methods
        var orderId = orderRepository.Save(order);
        orderItems
            .AsList()
            .ForEach(e => e.OrderId = orderId);
        _orderItemRepository.SaveAll(orderItems);

        // Commit
        _unitOfWork.Commit();
    }
    catch
    {
        // Rollback
        _unitOfWork.Rollback();
    }
}

Lastly, do not forget to as well inject the business logic as transient.

public void ConfigureServices(IServiceCollection services)
{
    services.SaveControllers();

    // Registration
    services.SaveTransient<ISalesManager, SalesManager>();
}

After the registration of the business logic, you can always pass it on the constructor of your controllers.

When working with UOW, you are obligated to always implement your own repository methods and call the repository methods underneath and explicitly pass the transaction object from the UOW object. You should avoid calling the normal operations of the repository directly as they are not a part of the transaction context. We in RepoDB are considering implementing the UOW in the near future versions, specifically the Attach() method mentioned on this page.