executable.md

title
Executable

The IExecutable and IExecutable<T> interfaces are intended to be used by data providers. These interfaces can abstract any kind of data source. The data or domain layer can wrap data in an executable and pass it to the GraphQL layer. A GraphQL resolver that returns an IExecutable<T> is recognized as a list.

public class User
{
    public string Name { get; }
}

public interface IUserRepository
{
    public IExecutable<User> FindAll();
}

public class Query
{
    public IExecutable<User> GetUsers([Service] IUserRepository repo) =>
        repo.FindAll();
}

type Query {
    users: [User!]!
}

This abstraction can be used to completely decouple the GraphQL layer form the database-specific knowledge.

Filtering, sorting, projections et al, can pick up the executable and apply logic to it. There is still a database-specific provider needed for these features, but it is opaque to the GraphQL layer.

The IExecutable is known to the execution engine. The engine calls ToListAsync, FirstOrDefault or SingleOrDefault on the executable. The executable shall execute it in the most efficient way for the database.

API

Source

    object Source { get; }

The source property stores the current state of the executable

In the EntityFramework executable this property holds the IQueryable. In the MongoExecutable it is the DbSet<T> or the IAggregateFluent<T>. Source is deliberately read-only. If you have a custom implementation of IExecutable and you want to set the Source, you should create a method that returns a new executable with the new source

ToListAsync

    ValueTask<IList> ToListAsync(CancellationToken cancellationToken);

Should return a list of <T>.

FirstOrDefault

    ValueTask<IList> FirstOrDefault(CancellationToken cancellationToken);

Should return the first element of a sequence, or a default value if the sequence contains no elements.

SingleOrDefault

    ValueTask<IList> SingleOrDefault(CancellationToken cancellationToken);

Should return the only element of a default value if no such element exists. This method should throw an exception if more than one element satisfies the condition.

Print

string Print();

Prints the executable in its current state

Example

public class EntityFrameworkExecutable<T> : QueryableExecutable<T>
{
    public IQueryable<T> Source { get; }

    object IExecutable.Source => Source;

    public EntityFrameworkExecutable(IQueryable<T> queryable) : base(queryable)
    {
    }

    /// <summary>
    /// Returns a new enumerable executable with the provided source
    /// </summary>
    /// <param name="source">The source that should be set</param>
    /// <returns>The new instance of an enumerable executable</returns>
    public QueryableExecutable<T> WithSource(IQueryable<T> source)
    {
        return new QueryableExecutable<T>(source);
    }

    public override async ValueTask<IList> ToListAsync(CancellationToken cancellationToken) =>
        await Source.ToListAsync(cancellationToken).ConfigureAwait(false);

    public override async ValueTask<object?> FirstOrDefaultAsync(
        CancellationToken cancellationToken) =>
        await Source.FirstOrDefaultAsync(cancellationToken).ConfigureAwait(false);

    public override async ValueTask<object?> SingleOrDefaultAsync(
        CancellationToken cancellationToken) =>
        await Source.SingleOrDefaultAsync(cancellationToken).ConfigureAwait(false);

    public override string Print() => Source.ToQueryString();
}