Georgia EPD-IT App Library

This repo contains a library created by Georgia EPD-IT to provide common classes and tools for our web applications.

(Much of this work was inspired by the ABP Framework.)

How to install

To install, search for "GaEpd.AppLibrary" in the NuGet package manager or run the following command:

dotnet add package GaEpd.AppLibrary

What's included

Domain entities

The following interfaces and abstract implementations of domain entities are provided for domain-driven design:

• The basic IEntity<TKey> interface defines an entity with a primary key of the given type.
• The special case IEntity interface defines an entity with a GUID primary key.
• IAuditableEntity<TUserKey> adds created/updated properties and methods for basic data auditing.
• ISoftDelete and ISoftDelete<TUserKey> add properties for "soft deleting" an entity rather than actually
• deleting it.
• INamedEntity adds a "Name" string property.
• IActiveEntity adds an "Active" boolean property.

There are also abstract classes based on the above interfaces from which you should derive your domain entities: Entity<TKey>, AuditableEntity<TKey, TUserKey>, SoftDeleteEntity<TKey, TUserKey>, AuditableSoftDeleteEntity<TKey, TUserKey>, and StandardNamedEntity.

The StandardNamedEntity class derives from AuditableEntity<Guid>, INamedEntity, and IActiveEntity, and includes methods for enforcing the length of the Name. Maximum and minimum length for the name can be set by overriding the default properties.

Example usage:

public class MyEntity : StandardNamedEntity
{
    public override int MinNameLength => 2;
    public override int MaxNameLength => 50;

    public MyEntity() { }
    public MyEntity(Guid id, string name) : base(id, name) { }
}

ValueObject

An abstract ValueObject record can help add value objects to your domain entities. A value object is a compound of properties, such as an address or date range, that are comparable based solely on their values rather than their references. The properties of a value object are typically stored with its parent class, not as a separate record with its own ID. Value objects should be treated as immutable. When deriving from ValueObject, you must override the GetEqualityComponents() method to define which properties to use to determine equality.

Example usage:

[Owned]
public record Address : ValueObject
{
    public string Street { get; init; } = string.Empty;
    public string? Street2 { get; init; }
    public string City { get; init; } = string.Empty;
    public string State { get; init; } = string.Empty;

    [DataType(DataType.PostalCode)]
    public string PostalCode { get; init; } = string.Empty;

    protected override IEnumerable<object> GetEqualityComponents()
    {
        yield return Street;
        yield return Street2 ?? string.Empty;
        yield return City;
        yield return State;
        yield return PostalCode;
    }
}

Note: The [Owned] attribute is an Entity Framework attribute defining this as a value object owned by the parent class. See Owned Entity Types for more info on how this is implemented in EF Core.

Data Repositories

Common data repository interfaces define basic entity CRUD operations.

• The IReadRepository interface defines various read-only operations: Get, Find, Count, Exists, GetList, and GetPagedList. (The Get and Find methods both return an entity, but Get enables the Entity Framework change tracker while Find disables it. Also, if an entity is not found, then Get throws an EntityNotFoundException while Find returns null. Read more about Tracking vs. No-Tracking Queries.)
• The IWriteRepository interface defines various write operations: Insert, Update, and Delete.
• IRepository combines the above read and write interfaces.
• INamedEntityRepository derives from IRepository and adds some methods useful for entities expected to have unique names (i.e., entities implementing INamedEntity).
• IReadRepositoryWithMapping adds overloads to the Find, GetList, and GetPagedList methods that use query projection to return data transfer objects (DTOs) rather than complete entities. Use of these methods enables Entity Framework to create much more efficient SQL queries.
• IRepositoryWithMapping and INamedEntityRepositoryWithMapping similarly include the query projection overloads.

Repository Implementations

There are two sets of abstract repository classes that implement the IRepository, IRepositoryWithMapping, INamedEntityRepository, and INamedEntityRepositoryWithMapping interfaces. Client applications can derive from either or both of these implementations.

• One set (in the LocalRepository namespace) uses in-memory data (convenient for use during development when the overhead of a database is undesirable).
• The other set (in the EFRepository namespace) requires an Entity Framework database context (DbContext).

Example usage:

// Define the repository interface.
public interface IMyRepository : INamedEntityRepository<MyEntity> { }

// Implement a version of the repository that uses in-memory data.
public sealed class MyInMemoryRepository 
    : LocalRepository.NamedEntityRepository<MyEntity>(MyEntitySeedData), IMyRepository;

// Implement another version that uses an Entity Framework database.
public sealed class MyEfRepository(AppDbContext context)
    : EFRepository.NamedEntityRepository<MyEntity, AppDbContext>(context), IMyRepository;

// Using dependency injection, choose which implementation to use based on the app environment, for example.
if (builder.Environment.IsDevelopment())
{
    builder.Services.AddSingleton<IMyRepository, MyInMemoryRepository>();    
}
else
{
    builder.Services.AddScoped<IMyRepository, MyEfRepository>();    
}

Predicate builder

Code from C# in a Nutshell is included to enable creating filter expressions that can be combined. The library comes with the commonly used filters WithId(id) for all entities and ExcludedDeleted() for "soft delete" entities.

Example usage:

public static Expression<Func<MyEntity, bool>> IsActive(this Expression<Func<MyEntity, bool>> predicate) =>
    predicate.And(e => e.IsActive);

public static Expression<Func<MyEntity, bool>> ActiveAndNotDeletedPredicate() =>
    PredicateBuilder.True<MyEntity>().IsActive().ExcludeDeleted();

Pagination classes

IPaginatedRequest and IPaginatedResult<T> define how to request and receive paginated (and sorted) search results.

The System.Linq.Dynamic.Core package is included.

List Item record

A ListItem<TKey> record type defines a key-value pair with fields for ID of type TKey and string Name. The ToSelectList() extension method takes a ListItem enumerable and returns an MVC SelectList which can be used to create an HTML <select> element.

Enum extensions

GetDisplayName() and GetDescription() return the DisplayAttribute.Name and DescriptionAttribute values of an enum, respectively.

Guard clauses

The GuardClauses package is included by reference.