Predecessors

When we defined the Construction.Project type, we used Jinaga.User as one of its properties. That made it a predecessor. In this case, the meaning of that predecessor relationship is that the user created the project.

Once you have predecessors, you can query for facts that are related to them. These, as you might have guessed, are called successors. You'll find the Successors extension method in the Jinaga.Extensions namespace.

Let's query for all projects that a user has created.

using Jinaga.Extensions;

// Create a couple more projects.
Project projectB = await j.Fact(new Project(user, Guid.NewGuid()));
Project projectC = await j.Fact(new Project(user, Guid.NewGuid()));

var projectsCreatedByUser = Given<User>.Match(u =>
    u.Successors().OfType<Project>(p => p.creator)
);

ImmutableList<Project> projects = await j.Query(projectsCreatedByUser, user);

Let's break down that specification. Start with Given and the parameter type. Then use Match to write an expression that matches the facts you want.

The Successors extension method finds all successors OfType<T> related to the given predecessor. Provide a lambda that shows how the successors relate to the predecessor.