# Persistence

#### Motivation

> A *repository* represents all objects of a certain type as a conceptual set (usually emulated). **It acts like a collection**, except with more elaborate querying capability. \[...] For each type of object that needs global access, **create an object that can provide the illusion of an in-memory collection** of all objects of that type.\
> \
> \&#xNAN;***Eric Evans - Domain Driven Design***

Most repository patterns contain many query methods, and they are often nearly identical to the DbContext class. Unlike the norm, the Eiffel framework follows a collection-oriented repository approach."

Each repository should expose a single aggregate, and the maintenance of the entities or value objects should be handled by the owner aggregate.<br>

```csharp
/// <summary>
/// IRepository interface
/// </summary>
/// <typeparam name="TAggregate">The type of aggregate</typeparam>
/// <typeparam name="TIdentity">The tpye of aggregate identity</typeparam>
/// <typeparam name="TKey">The type of database primary key</typeparam>
public interface IRepository<TAggregate, TIdentity, TKey>
    where TKey : struct, IEquatable<TKey>
    where TIdentity : class
    where TAggregate : Aggregate<TIdentity, TKey>
{
    /// <summary>
    /// Gets record from database
    /// </summary>
    /// <param name="identity">Aggregate</param>
    /// <param name="cancellationToken">Cancellation token</param>
    Task<TAggregate> GetAsync(TIdentity identity, CancellationToken cancellationToken = default);

    /// <summary>
    /// Adds record to database
    /// </summary>
    /// <param name="aggregate">Aggregate identifier</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Record from database</returns>
    Task AddAsync(TAggregate aggregate, CancellationToken cancellationToken = default);


    /// <summary>
    /// Commit changes to database
    /// </summary>
    /// <param name="aggregate">Aggregate</param>
    /// <param name="cancellationToken">Cancellation token</param>
    Task SaveChangesAsync(TAggregate aggregate, CancellationToken cancellationToken = default);
}
```


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