Discourse (discourse/discourse)

Discourse

https://github.com/discourse/discourse
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# Discourse

Discourse is a 100% open-source community platform built with Ruby on Rails (backend API) and Ember.js (frontend). It provides discussion forums with real-time chat, customizable themes, and an extensible plugin system. The platform supports topics, posts, categories, user management, groups, badges, and advanced search capabilities, all exposed through a comprehensive REST API.

The architecture follows a standard Rails MVC pattern with controllers handling JSON API responses, services encapsulating business logic, and models managing data persistence via PostgreSQL. The frontend uses Ember.js components that communicate with the Rails API. Discourse offers extensive customization through its Plugin API (JavaScript) for frontend modifications and Ruby plugins for backend extensions, making it highly adaptable for various community needs.

## REST API - Topics

The Topics API allows creating, reading, updating, and managing discussion topics. Topics are the primary content containers in Discourse, each containing a title, category, and collection of posts.

```bash
# Create a new topic
curl -X POST "https://discourse.example.com/posts.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{
    "title": "Welcome to our community",
    "raw": "This is the content of the first post in the topic.",
    "category": 5,
    "tags": [{"name": "welcome"}, {"name": "announcement"}]
  }'

# Get a topic by ID
curl "https://discourse.example.com/t/123.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Update topic title/category
curl -X PUT "https://discourse.example.com/t/123.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{
    "topic_id": 123,
    "title": "Updated Topic Title",
    "category_id": 10,
    "tags": [{"id": 1, "name": "updated"}]
  }'

# Close/Open a topic
curl -X PUT "https://discourse.example.com/t/123/status.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{"status": "closed", "enabled": true}'

# Delete a topic
curl -X DELETE "https://discourse.example.com/t/123.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Set topic timer (auto-close)
curl -X POST "https://discourse.example.com/t/123/timer.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{"status_type": "close", "time": "2024-12-31T23:59:59Z"}'
```

## REST API - Posts

The Posts API manages individual posts within topics. Posts contain the actual content of discussions and support features like editing, deletion, recovery, and revision history.

```bash
# Create a reply to a topic
curl -X POST "https://discourse.example.com/posts.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{
    "topic_id": 123,
    "raw": "This is a reply to the topic.",
    "reply_to_post_number": 1
  }'

# Get a single post
curl "https://discourse.example.com/posts/456.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Update/Edit a post
curl -X PUT "https://discourse.example.com/posts/456.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{
    "post": {
      "raw": "Updated post content with edits.",
      "edit_reason": "Fixed typos"
    }
  }'

# Delete a post
curl -X DELETE "https://discourse.example.com/posts/456.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Recover a deleted post
curl -X PUT "https://discourse.example.com/posts/456/recover.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Get post revisions
curl "https://discourse.example.com/posts/456/revisions/2.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Get latest posts feed
curl "https://discourse.example.com/posts.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"
```

## REST API - Categories

The Categories API manages topic categories which organize discussions. Categories support permissions, subcategories, custom colors, and various display settings.

```bash
# List all categories
curl "https://discourse.example.com/categories.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Get a specific category by slug
curl "https://discourse.example.com/c/general/find_by_slug.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Create a new category
curl -X POST "https://discourse.example.com/categories.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Announcements",
    "color": "0088CC",
    "text_color": "FFFFFF",
    "description": "Official announcements from the team",
    "permissions": {"everyone": 1},
    "parent_category_id": null
  }'

# Update a category
curl -X PUT "https://discourse.example.com/categories/5.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Updated Category Name",
    "color": "FF5733",
    "slug": "updated-slug"
  }'

# Delete a category (must be empty)
curl -X DELETE "https://discourse.example.com/categories/5.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Search categories
curl -X POST "https://discourse.example.com/categories/search.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{"term": "general", "limit": 10}'
```

## REST API - Users

The Users API handles user account management including creation, profile updates, authentication, and user-specific data retrieval.

```bash
# Get user by username
curl "https://discourse.example.com/u/johndoe.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Create a new user
curl -X POST "https://discourse.example.com/users.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "John Doe",
    "username": "johndoe",
    "email": "john@example.com",
    "password": "securepassword123",
    "active": true,
    "approved": true
  }'

# Update user profile
curl -X PUT "https://discourse.example.com/u/johndoe.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "John Smith",
    "bio_raw": "Hello, I am a community member!"
  }'

# Get user's summary/stats
curl "https://discourse.example.com/u/johndoe/summary.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# List user's bookmarks
curl "https://discourse.example.com/u/johndoe/bookmarks.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: johndoe"

# Get user cards (multiple users)
curl "https://discourse.example.com/u/cards.json?user_ids=1,2,3" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"
```

## REST API - Groups

The Groups API manages user groups for permissions, messaging, and community organization. Groups can be automatic (trust level based) or custom.

```bash
# List all groups
curl "https://discourse.example.com/groups.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Get a specific group
curl "https://discourse.example.com/groups/moderators.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Create a new group (admin only)
curl -X POST "https://discourse.example.com/admin/groups.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{
    "group": {
      "name": "vip_members",
      "full_name": "VIP Members",
      "visibility_level": 0,
      "mentionable_level": 0,
      "messageable_level": 0
    }
  }'

# Add members to a group
curl -X PUT "https://discourse.example.com/groups/5/members.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{"usernames": "johndoe,janedoe"}'

# Remove member from group
curl -X DELETE "https://discourse.example.com/groups/5/members.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system" \
  -H "Content-Type: application/json" \
  -d '{"username": "johndoe"}'

# Get group members
curl "https://discourse.example.com/groups/moderators/members.json" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"
```

## REST API - Search

The Search API provides full-text search across topics, posts, users, categories, and tags with support for advanced search operators.

```bash
# Basic search
curl "https://discourse.example.com/search.json?q=ruby%20programming" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Search with filters
curl "https://discourse.example.com/search.json?q=ruby%20category:programming%20status:open" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Header search (quick search)
curl "https://discourse.example.com/search/query.json?term=help" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Search within a specific category
curl "https://discourse.example.com/search.json?q=help&search_context[type]=category&search_context[id]=5" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Search within a user's posts
curl "https://discourse.example.com/search.json?q=@johndoe%20tutorial" \
  -H "Api-Key: YOUR_API_KEY" \
  -H "Api-Username: system"

# Advanced search operators:
# category:name - filter by category
# #tag - filter by tag
# @username - filter by author
# status:open/closed/archived
# before:YYYY-MM-DD / after:YYYY-MM-DD
# in:title/first/pinned/wiki
# order:latest/likes/views
```

## JavaScript Plugin API - Basic Setup

The Plugin API allows themes and plugins to customize Discourse's frontend behavior. Plugins are initialized through API initializers that receive the `api` object with all customization methods.

```javascript
// plugins/my-plugin/assets/javascripts/discourse/api-initializers/init-my-plugin.gjs
import { apiInitializer } from "discourse/lib/api";

export default apiInitializer((api) => {
  // Get current user
  const currentUser = api.getCurrentUser();
  console.log("Current user:", currentUser?.username);

  // Modify a class (add new behavior to existing components)
  api.modifyClass("controller:composer", {
    pluginId: "my-plugin",

    // Override or extend actions
    actions: {
      customAction() {
        console.log("Custom action triggered!");
      }
    }
  });

  // Listen for page changes (useful for analytics)
  api.onPageChange((url, title) => {
    console.log(`Page changed to: ${url} - ${title}`);
  });

  // Listen for application events
  api.onAppEvent("topic:created", (topic) => {
    console.log("New topic created:", topic.id);
  });
});
```

## JavaScript Plugin API - Value Transformers

Value transformers allow modifying data values at specific points in the application without replacing entire components. They're the preferred way to customize UI elements.

```javascript
import { apiInitializer } from "discourse/lib/api";

export default apiInitializer((api) => {
  // Transform a value - modify post menu buttons
  api.registerValueTransformer("post-menu-buttons", ({ value, context }) => {
    const { post } = context;

    // Add a custom button to posts
    if (post.user_id === api.getCurrentUser()?.id) {
      value.push({
        id: "my-custom-button",
        icon: "star",
        label: "my_plugin.favorite",
        action: "favoritePost"
      });
    }

    return value;
  });

  // Transform poster name icons
  api.registerValueTransformer("poster-name-icons", ({ value, context }) => {
    const { post } = context;

    if (post.user_custom_fields?.is_vip) {
      return [...value, { icon: "crown", className: "vip-badge", title: "VIP Member" }];
    }

    return value;
  });

  // Add tracked properties for automatic UI updates
  api.addTrackedPostProperties("custom_field", "special_status");
  api.addTrackedTopicProperties("custom_topic_field");
});
```

## JavaScript Plugin API - Behavior Transformers

Behavior transformers allow intercepting and modifying application behavior at specific points. They can run code before, after, or instead of default behavior.

```javascript
import { apiInitializer } from "discourse/lib/api";

export default apiInitializer((api) => {
  // Intercept behavior - perform action before default behavior
  api.registerBehaviorTransformer("example-transformer", ({ next, context }) => {
    console.log("Running before default behavior", context);

    const result = next(); // Execute default behavior

    console.log("Running after default behavior");
    return result;
  });

  // Conditionally abort default behavior
  api.registerBehaviorTransformer("post-submit", ({ next, context }) => {
    const { composer } = context;

    // Prevent submission under certain conditions
    if (composer.raw?.includes("forbidden_word")) {
      alert("Your post contains forbidden content!");
      return; // Don't call next() - aborts default behavior
    }

    return next(); // Continue with normal submission
  });

  // Add behavior transformer name (must be in pre-initializer)
  // This registers a new transformer point that plugins can hook into
  api.addBehaviorTransformerName("my-custom-behavior-point");
});
```

## JavaScript Plugin API - UI Customization

The Plugin API provides methods to customize the user interface including toolbar buttons, icons, decorators, and rendered content.

```javascript
import { apiInitializer } from "discourse/lib/api";
import MyCustomComponent from "../components/my-component";

export default apiInitializer((api) => {
  // Add toolbar button to composer
  api.onToolbarCreate((toolbar) => {
    toolbar.addButton({
      id: "insert-template",
      group: "extras",
      icon: "file-alt",
      action: "insertTemplate",
      title: "my_plugin.insert_template"
    });
  });

  // Add option to composer popup menu
  api.addComposerToolbarPopupMenuOption({
    icon: "magic",
    label: "my_plugin.format_text",
    action: (toolbarEvent) => {
      toolbarEvent.applySurround("**", "**");
    },
    condition: (composer) => composer.editingPost
  });

  // Decorate cooked (rendered) post content
  api.decorateCookedElement((element, decoratorHelper) => {
    // Add click handlers to custom elements
    element.querySelectorAll(".custom-element").forEach((el) => {
      el.addEventListener("click", () => {
        console.log("Custom element clicked");
      });
    });

    // Return cleanup function (optional)
    return () => {
      element.querySelectorAll(".custom-element").forEach((el) => {
        el.removeEventListener("click", () => {});
      });
    };
  }, { onlyStream: true });

  // Replace icons globally
  api.replaceIcon("heart", "thumbs-up");

  // Render a component in a plugin outlet
  api.renderInOutlet("user-profile-primary", MyCustomComponent);

  // Add keyboard shortcut
  api.addKeyboardShortcut("ctrl+shift+t", () => {
    console.log("Custom shortcut triggered!");
  }, { global: true });
});
```

## JavaScript Plugin API - Admin & Navigation

The Plugin API allows adding custom admin interfaces, sidebar sections, and navigation items.

```javascript
import { apiInitializer } from "discourse/lib/api";

export default apiInitializer((api) => {
  // Add admin menu button for posts
  api.addPostAdminMenuButton((post) => {
    return {
      icon: "flag",
      className: "custom-flag-button",
      label: "my_plugin.custom_flag",
      action: () => {
        console.log("Custom flag action for post:", post.id);
      }
    };
  });

  // Add admin menu button for topics
  api.addTopicAdminMenuButton((topic) => {
    return {
      icon: "archive",
      className: "archive-topic",
      label: "my_plugin.archive_topic",
      action: () => {
        // Perform archive action
      }
    };
  });

  // Add navigation item
  api.addNavigationBarItem({
    name: "my-custom-page",
    displayName: "Custom Page",
    href: "/custom-page"
  });

  // Add sidebar section
  api.addSidebarSection((BaseCustomSidebarSection, BaseCustomSidebarSectionLink) => {
    return class extends BaseCustomSidebarSection {
      get name() {
        return "my-plugin-section";
      }

      get title() {
        return "My Plugin";
      }

      get links() {
        return [
          new (class extends BaseCustomSidebarSectionLink {
            get name() { return "custom-link"; }
            get title() { return "Custom Link"; }
            get href() { return "/custom-page"; }
            get icon() { return "star"; }
          })()
        ];
      }
    };
  });
});
```

## Ruby Plugin Development - Basic Structure

Ruby plugins extend Discourse's backend functionality. A plugin requires a `plugin.rb` manifest file and can add controllers, models, jobs, and modify core behavior through events and modifiers.

```ruby
# plugins/my-plugin/plugin.rb
# name: my-plugin
# about: A custom plugin for Discourse
# version: 1.0.0
# authors: Your Name
# url: https://github.com/yourname/my-plugin
# required_version: 2.7.0

enabled_site_setting :my_plugin_enabled

# Register plugin assets
register_asset "stylesheets/my-plugin.scss"

# Add site settings
after_initialize do
  # Add custom fields to models
  Topic.register_custom_field_type("my_custom_field", :string)
  Post.register_custom_field_type("special_status", :boolean)
  User.register_custom_field_type("user_preference", :integer)

  # Whitelist custom fields for serialization
  add_to_serializer(:topic_view, :my_custom_field) do
    object.topic.custom_fields["my_custom_field"]
  end

  add_to_serializer(:post, :special_status) do
    object.custom_fields["special_status"]
  end

  # Register event listeners
  on(:post_created) do |post, opts, user|
    if post.raw.include?("#important")
      post.custom_fields["special_status"] = true
      post.save_custom_fields
    end
  end

  on(:topic_created) do |topic, opts, user|
    # Perform actions when topic is created
    Jobs.enqueue(:process_new_topic, topic_id: topic.id)
  end

  # Add permitted parameters to controllers
  PostsController.class_eval do
    def permitted_create_params
      super + [:my_custom_param]
    end
  end
end
```

## Ruby Plugin Development - Controllers and Routes

Plugins can add custom controllers and routes to handle API endpoints and web pages.

```ruby
# plugins/my-plugin/plugin.rb
after_initialize do
  # Define the controller
  module ::MyPlugin
    class Engine < ::Rails::Engine
      engine_name "my_plugin"
      isolate_namespace MyPlugin
    end

    class MyController < ::ApplicationController
      requires_login

      def index
        items = MyPlugin::Item.where(user_id: current_user.id)
        render json: { items: items }
      end

      def create
        params.require(:item).permit(:name, :description)

        item = MyPlugin::Item.create!(
          user_id: current_user.id,
          name: params[:item][:name],
          description: params[:item][:description]
        )

        render json: { item: item }
      end

      def show
        item = MyPlugin::Item.find(params[:id])
        guardian.ensure_can_see!(item)

        render json: { item: item }
      end

      def destroy
        item = MyPlugin::Item.find(params[:id])
        guardian.ensure_can_edit!(item)

        item.destroy!
        render json: success_json
      end
    end
  end

  # Add routes
  Discourse::Application.routes.append do
    mount ::MyPlugin::Engine, at: "/my-plugin"
  end

  MyPlugin::Engine.routes.draw do
    get "/" => "my#index"
    post "/" => "my#create"
    get "/:id" => "my#show"
    delete "/:id" => "my#destroy"
  end
end
```

## Ruby Plugin Development - Site Settings

Plugins can define custom site settings that administrators can configure through the admin panel.

```yaml
# plugins/my-plugin/config/settings.yml
my_plugin:
  my_plugin_enabled:
    default: false
    client: true

  my_plugin_api_key:
    default: ""
    secret: true

  my_plugin_max_items:
    default: 10
    min: 1
    max: 100

  my_plugin_feature_mode:
    default: "basic"
    type: enum
    choices:
      - basic
      - advanced
      - expert

  my_plugin_allowed_groups:
    default: ""
    type: group_list

  my_plugin_welcome_message:
    default: "Welcome to our community!"
    type: text

  my_plugin_categories:
    default: ""
    type: category_list
```

```ruby
# Using settings in plugin code
after_initialize do
  if SiteSetting.my_plugin_enabled
    max_items = SiteSetting.my_plugin_max_items
    allowed_groups = SiteSetting.my_plugin_allowed_groups.split("|")

    # Check if user is in allowed groups
    def user_allowed?(user)
      return true if allowed_groups.empty?
      (user.groups.pluck(:name) & allowed_groups).any?
    end
  end
end
```

## Theme Settings

Themes can define settings that site administrators can customize through the UI without modifying code. Settings are defined in YAML and accessible in JavaScript and CSS.

```yaml
# themes/my-theme/settings.yml

# Simple boolean setting
show_banner: true

# String setting
banner_text: "Welcome to our community!"

# Integer with limits
max_featured_topics:
  type: integer
  default: 5
  min: 1
  max: 20

# Float setting
content_opacity:
  type: float
  default: 0.9

# Enum (dropdown) setting
theme_style:
  type: enum
  default: modern
  choices:
    - classic
    - modern
    - minimal

# List setting (user can add/remove items)
featured_categories:
  type: list
  default: "general|announcements"

# Upload setting (for images)
custom_logo:
  type: upload

# Multi-language description
primary_color:
  type: string
  default: "#0088CC"
  description:
    en: "The primary brand color for the theme"
    es: "El color principal de la marca"
    fr: "La couleur principale de la marque"
```

```javascript
// Accessing settings in JavaScript
// themes/my-theme/javascripts/discourse/api-initializers/init-theme.gjs
import { apiInitializer } from "discourse/lib/api";

export default apiInitializer((api) => {
  // Settings are available globally as `settings` object
  console.log("Theme settings:", settings);

  if (settings.show_banner) {
    console.log("Banner text:", settings.banner_text);
  }

  const maxTopics = settings.max_featured_topics;
  const themeStyle = settings.theme_style;
});
```

```scss
// Accessing settings in SCSS
// themes/my-theme/common/common.scss

// Settings are available as SCSS variables
html {
  --primary-color: #{$primary-color};
  --content-opacity: #{$content-opacity};
}

.custom-banner {
  background-color: $primary-color;
  opacity: $content-opacity;
}

@if $show-banner {
  .banner-container {
    display: block;
  }
}
```

## Discourse Service Objects

Service objects encapsulate complex business logic and provide a consistent pattern for operations that span multiple models. They use a contract-based approach with validation and step-based execution.

```ruby
# Example service object pattern used in Discourse
# app/services/example/create_item.rb
module Example
  class CreateItem
    include Service::Base

    # Define the contract (input validation)
    params do
      attribute :name, :string
      attribute :description, :string
      attribute :category_id, :integer

      validates :name, presence: true, length: { maximum: 100 }
      validates :category_id, presence: true
    end

    # Define dependencies
    model :category
    model :user

    # Define policies (authorization)
    policy :can_create

    # Define the transaction
    transaction do
      step :create_item
      step :notify_users
      step :log_action
    end

    private

    def fetch_category(params:)
      Category.find_by(id: params.category_id)
    end

    def fetch_user
      guardian.user
    end

    def can_create(guardian:, category:)
      guardian.can_create_topic_on_category?(category)
    end

    def create_item(params:, category:, user:)
      context[:item] = Item.create!(
        name: params.name,
        description: params.description,
        category: category,
        user: user
      )
    end

    def notify_users(item:)
      # Send notifications
    end

    def log_action(item:, user:)
      StaffActionLogger.new(user).log_item_creation(item)
    end
  end
end

# Using the service in a controller
class ItemsController < ApplicationController
  def create
    Example::CreateItem.call(guardian:, params: item_params) do
      on_success { |item:| render json: { item: item } }
      on_failed_contract { |contract| render_json_error(contract.errors) }
      on_failed_policy(:can_create) { raise Discourse::InvalidAccess }
      on_failure { render json: failed_json }
    end
  end
end
```

Discourse is primarily used to build online community forums, providing features like threaded discussions, real-time chat, user trust levels, and moderation tools. Common integrations include SSO authentication with external systems, webhook notifications for external services, and embedding Discourse comments into external websites. The platform excels at creating communities for open-source projects, customer support forums, internal team discussions, and knowledge bases.

The extensibility model allows developers to create themes for visual customization, plugins for adding new features, and integrations with external services through the REST API. The JavaScript Plugin API enables frontend modifications without forking core code, while Ruby plugins can add new database models, background jobs, and server-side logic. This architecture makes Discourse suitable for both simple community forums and complex, highly-customized platforms with unique requirements.