Model Classes in AD4M

Model classes in AD4M provide a way to define, store, and query structured data in your application. Let's start with a simple example that we'll build upon:

Quick Start

Here's a basic recipe model:

import { Ad4mModel, ModelOptions, Property } from '@coasys/ad4m';
 
@ModelOptions({ name: "Recipe" })
class Recipe extends Ad4mModel {
  @Property({
    through: "recipe://name",
    resolveLanguage: "literal"
  })
  name: string = "";
}
 
// Using the model
const recipe = new Recipe(perspective);
recipe.name = "Chocolate Cake";
await recipe.save();
 
// Reading it back
const recipes = await Recipe.findAll(perspective);
console.log(recipes[0].name); // "Chocolate Cake"

Before using any model class, register it with your perspective:

await perspective.ensureSDNASubjectClass(Recipe);

Basic Concepts

Properties

Properties are the basic building blocks of your models. They can be required or optional:

@ModelOptions({ name: "Recipe" })
class Recipe extends Ad4mModel {
  // Required property
  @Property({
    through: "recipe://name",
    resolveLanguage: "literal"
  })
  name: string = "";
 
  // Optional property
  @Optional({
    through: "recipe://description",
    resolveLanguage: "literal"
  })
  description?: string;
}

Collections

Collections represent one-to-many relationships:

@ModelOptions({ name: "Recipe" })
class Recipe extends Ad4mModel {
  @Property({
    through: "recipe://name",
    resolveLanguage: "literal"
  })
  name: string = "";
 
  @Collection({ through: "recipe://ingredient" })
  ingredients: string[] = [];
}
 
// Using collections
const recipe = new Recipe(perspective);
recipe.name = "Chocolate Cake";
recipe.ingredients = ["flour", "sugar", "cocoa"];
await recipe.save();

Working with Models

Creating & Saving

// Create new instance
const recipe = new Recipe(perspective);
recipe.name = "Chocolate Cake";
await recipe.save();
 
// Create with specific ID
const recipe = new Recipe(perspective, "recipe://chocolate-cake");
await recipe.save();

Reading & Updating

// Get by ID
const recipe = new Recipe(perspective, existingId);
await recipe.get();
 
// Update
recipe.name = "Dark Chocolate Cake";
await recipe.update();

Basic Querying

// Get all recipes
const allRecipes = await Recipe.findAll(perspective);
 
// Get with simple conditions
const recipes = await Recipe.findAll(perspective, {
  where: { name: "Chocolate Cake" }
});

Understanding the Underlying System

Now that you've seen the basics, let's understand how it works under the hood.

Graph-Based Storage

Each model instance is stored as a subgraph in an AD4M perspective. For example, our recipe is stored as:

recipe://chocolate-cake-123 -[recipe://name]-> literal://string:"Chocolate Cake"
recipe://chocolate-cake-123 -[recipe://ingredient]-> ingredient://flour
recipe://chocolate-cake-123 -[recipe://ingredient]-> ingredient://sugar

Every node in this graph is a URL pointing to an Expression in some language.

Base Expressions

Each model instance has a unique identifier called a "base expression" that serves as the root node of its subgraph. You can specify it or let AD4M generate one:

// Auto-generated base expression
const recipe = new Recipe(perspective);
 
// Custom base expression
const recipe = new Recipe(perspective, "recipe://chocolate-cake-2024-03");

Literals for Simple Values

AD4M provides Literals for storing simple values without needing a full language:

// These are equivalent:
recipe.name = "Chocolate Cake";
// Stored as: literal://string:Chocolate Cake
 
recipe.cookingTime = 45;
// Stored as: literal://number:45

Advanced Features

Property Types

AD4M provides several specialized property decorators:

@ReadOnly

For computed or immutable properties:

@ReadOnly({
  through: "recipe://rating",
  getter: `
    findall(Rating, triple(Base, "recipe://user_rating", Rating), Ratings),
    sum_list(Ratings, Sum),
    length(Ratings, Count),
    Value is Sum / Count
  `
})
averageRating: number = 0;

@Flag

For immutable type markers:

@Flag({
  through: "ad4m://type",
  value: "recipe://main-course"
})
type: string = "";

Advanced Collections

Collections can be filtered and typed:

// Collection of other model instances
@Collection({
  through: "recipe://comment",
  where: { isInstance: Comment }
})
comments: Comment[] = [];
 
// Collection with custom filter
@Collection({
  through: "recipe://review",
  where: { condition: `triple(Target, "review://rating", Rating), Rating > 4` }
})
topReviews: string[] = [];

Advanced Querying

The query builder provides a fluent interface for complex queries:

const recipes = await Recipe.query(perspective)
  .where({ 
    category: "MainCourse",
    rating: { gt: 4 }
  })
  .order({ createdAt: "DESC" })
  .limit(5)
  .get();

Real-time Updates

Subscribe to changes in your data:

await Recipe.query(perspective)
  .where({ status: "cooking" })
  .subscribe(recipes => {
    console.log("Currently cooking:", recipes);
  });

Under the Hood

Social DNA and Prolog

When you define a model class, AD4M generates a Social DNA (SDNA) representation in Prolog:

@ModelOptions({ name: "Recipe" })
class Recipe extends Ad4mModel {
  @Property({
    through: "recipe://name",
    resolveLanguage: "literal",
    required: true
  })
  name: string = "";
}

Relationship with SHACL and Linked Data

AD4M's model classes share concepts with SHACL (Shapes Constraint Language):

Both define property constraints and validation rules
Both work with graph-based data
AD4M adds TypeScript integration, CRUD operations, and real-time features

Best Practices

Use Meaningful Predicates: Structure your predicate URIs logically:

through: "recipe://name"      // Good
through: "myapp://x"          // Bad

Type Safety: Always define proper TypeScript types:

@Property({ through: "recipe://servings" })
servings: number = 0;         // Good
 
@Property({ through: "recipe://servings" })
servings: any;               // Bad

Collection Filtering: Use where conditions to filter collections:

@Collection({
  through: "recipe://review",
  where: { isInstance: Review }  // Only include Review instances
})
reviews: Review[] = [];

Query Optimization: Use specific queries instead of filtering in memory:

// Good
const topRated = await Recipe.query(perspective)
  .where({ rating: { gt: 4 } })
  .get();
 
// Bad
const all = await Recipe.findAll(perspective);
const topRated = all.filter(r => r.rating > 4);

Subscriptions: Clean up subscriptions when they're no longer needed:

const subscription = await Recipe.query(perspective)
  .where({ status: "active" })
  .subscribe(recipes => {
    // Handle updates
  });
 
// Later...
subscription.unsubscribe();

Use Literals Appropriately:

// Good - Using literals for simple values
@Property({
  through: "recipe://name",
  resolveLanguage: "literal"
})
name: string = "";
 
// Good - Using specific language for rich content
@Property({
  through: "recipe://instructions",
  resolveLanguage: "markdown"
})
instructions: string = "";

Meaningful Base Expressions:

// Good - Descriptive base expression
const recipe = new Recipe(perspective, "recipe://chocolate-cake-2024-03");
 
// Bad - Random or meaningless base expression
const recipe = new Recipe(perspective, "x://123");

Error Handling

Always handle potential errors when working with models:

try {
  const recipe = new Recipe(perspective);
  recipe.name = "Failed Recipe";
  await recipe.save();
} catch (error) {
  console.error("Failed to save recipe:", error);
  // Handle error appropriately
}

Integration with AD4M Perspectives

Before using a model class, register it with the perspective:

// Register the model class
await perspective.ensureSDNASubjectClass(Recipe);
 
// Now you can use it
const recipe = new Recipe(perspective);
await recipe.save();

This ensures the perspective knows how to handle instances of your model class.

4 Change Listener Hooking up models to the UI