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 name length can be set in the constructor.

Example usage:

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

    public DerivedNamedEntity() { }
    public DerivedNamedEntity(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 provide a 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 get and search operations (including paginated search). The IWriteRepository interface defines insert, update, and delete operations. IRepository combines the read and write interfaces. Finally, the INamedEntityRepository adds a find-by-name method.

(Note that these interfaces work directly with domain entities. Your application should define application/domain services that define how the application interacts with the entities & repositories through data transfer objects (DTOs).)

There are two abstract BaseRepository classes that each implement the IRepository interface, one using in-memory data and the other requiring an Entity Framework database context.

There are similarly two abstract NamedEntityRepository classes that each implement the INamedEntityRepository interface.

Example usage:

public interface IDerivedRepository : INamedEntityRepository<DerivedNamedEntity> { }

public sealed class DerivedRepository : NamedEntityRepository<DerivedNamedEntity, AppDbContext>, IDerivedRepository
{
    public DerivedRepository(AppDbContext context) : base(context) { }
}

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.

What's not included

The File Service and GuardClauses packages have been moved to separate repositories.