Add comprehensive mixin documentation with timestamps and soft delete patterns

demo/mixins/README.md

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+# Mixins Demo
+
+This demo showcases NormalJS mixin patterns for reusable model behavior.
+
+## What's Included
+
+### Mixins
+
+1. **Timestampable** - Automatically manages `created_at` and `updated_at` fields
+2. **SoftDeletable** - Implements soft delete by overriding `unlink()` method
+
+### Models
+
+1. **User** - Uses Timestampable mixin
+2. **Document** - Uses both Timestampable and SoftDeletable mixins
+
+## Running the Demo
+
+```bash
+cd demo/mixins
+node index.js
+```
+
+## Key Concepts Demonstrated
+
+### 1. Timestampable Mixin
+
+- Adds `created_at` and `updated_at` fields
+- Automatically updates `updated_at` on record changes
+- Uses lifecycle hooks (`pre_create`, `pre_update`)
+
+### 2. SoftDeletable Mixin
+
+- Adds `deleted_at` field
+- Overrides `unlink()` to set `deleted_at` instead of deleting
+- Provides `restore()` method to undelete records
+- Provides `forceUnlink()` for hard deletes
+- Includes `isDeleted` getter
+- Uses default scope to hide soft-deleted records
+
+### 3. Combining Mixins
+
+- Models can use multiple mixins
+- Fields and methods are merged
+- Lifecycle hooks are called in order
+
+## Learn More
+
+See the [Mixins Documentation](../../docs/mixins.md) for detailed usage and examples.

demo/mixins/index.js

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+const { Connection, Repository } = require('../../dist/index');
+
+// Import mixins
+const Timestampable = require('./models/Timestampable');
+const SoftDeletable = require('./models/SoftDeletable');
+
+// Import models
+const User = require('./models/User');
+const Document = require('./models/Document');
+
+async function main() {
+  console.log('=== NormalJS Mixins Demo ===\n');
+
+  // Setup connection and repository
+  const conn = new Connection({
+    client: 'sqlite3',
+    connection: { filename: ':memory:' },
+    useNullAsDefault: true
+  });
+
+  const repo = new Repository(conn);
+
+  // Register mixins first
+  repo.register(Timestampable);
+  repo.register(SoftDeletable);
+
+  // Register models
+  repo.register(User);
+  repo.register(Document);
+
+  // Sync schema
+  await repo.sync({ force: true });
+
+  // Get models
+  const Users = repo.get('User');
+  const Documents = repo.get('Document');
+
+  console.log('1. Testing Timestampable Mixin');
+  console.log('================================\n');
+
+  // Create a user (timestamps are automatically set)
+  const user = await Users.create({
+    email: 'john@example.com',
+    name: 'John Doe'
+  });
+
+  console.log(`Created user: ${user.displayName}`);
+  console.log(`  created_at: ${user.created_at.toISOString()}`);
+  console.log(`  updated_at: ${user.updated_at.toISOString()}`);
+
+  // Wait a bit to see the timestamp difference
+  await new Promise(resolve => setTimeout(resolve, 100));
+
+  // Update the user (updated_at is automatically updated)
+  await user.write({ name: 'Jane Doe' });
+
+  console.log(`\nUpdated user: ${user.displayName}`);
+  console.log(`  created_at: ${user.created_at.toISOString()}`);
+  console.log(`  updated_at: ${user.updated_at.toISOString()}`);
+  console.log('  (Note: updated_at changed, created_at stayed the same)\n');
+
+  console.log('2. Testing SoftDeletable Mixin');
+  console.log('================================\n');
+
+  // Create a document
+  const doc = await Documents.create({
+    title: 'Important Document',
+    content: 'This is important content.',
+    author_id: user.id
+  });
+
+  console.log(`Created document: ${doc.title}`);
+  console.log(`  id: ${doc.id}`);
+  console.log(`  deleted_at: ${doc.deleted_at}`);
+  console.log(`  isDeleted: ${doc.isDeleted}\n`);
+
+  // Soft delete the document
+  await doc.unlink();
+
+  console.log('After soft delete:');
+  console.log(`  deleted_at: ${doc.deleted_at?.toISOString()}`);
+  console.log(`  isDeleted: ${doc.isDeleted}\n`);
+
+  // Try to find the document (should not be found due to default scope)
+  const foundDoc = await Documents.where({ id: doc.id }).first();
+  console.log(`Document found with normal query: ${foundDoc !== null}`);
+
+  // Find with unscoped (bypasses default scope)
+  const unscopedDoc = await Documents.unscoped().where({ id: doc.id }).first();
+  console.log(`Document found with unscoped query: ${unscopedDoc !== null}\n`);
+
+  // Restore the document
+  await unscopedDoc.restore();
+
+  console.log('After restore:');
+  console.log(`  deleted_at: ${unscopedDoc.deleted_at}`);
+  console.log(`  isDeleted: ${unscopedDoc.isDeleted}\n`);
+
+  // Now it should be found with normal queries
+  const restoredDoc = await Documents.where({ id: doc.id }).first();
+  console.log(`Document found after restore: ${restoredDoc !== null}\n`);
+
+  console.log('3. Testing Hard Delete');
+  console.log('================================\n');
+
+  // Soft delete again
+  await restoredDoc.unlink();
+  console.log('Soft deleted again');
+
+  // Get the document via unscoped
+  const docToDelete = await Documents.unscoped().where({ id: doc.id }).first();
+
+  // Hard delete (actually remove from database)
+  await docToDelete.forceUnlink();
+  console.log('Hard deleted (removed from database)');
+
+  // Try to find with unscoped (should not be found)
+  const finalCheck = await Documents.unscoped().where({ id: doc.id }).first();
+  console.log(`Document found after hard delete: ${finalCheck !== null}\n`);
+
+  console.log('4. Testing Combined Mixins');
+  console.log('================================\n');
+
+  // Create another document to show both mixins working together
+  const doc2 = await Documents.create({
+    title: 'Test Document',
+    content: 'Testing timestamps + soft delete',
+    author_id: user.id
+  });
+
+  console.log(`Created document: ${doc2.title}`);
+  console.log(`  created_at: ${doc2.created_at.toISOString()}`);
+  console.log(`  updated_at: ${doc2.updated_at.toISOString()}`);
+  console.log(`  deleted_at: ${doc2.deleted_at}\n`);
+
+  await new Promise(resolve => setTimeout(resolve, 100));
+
+  // Update it
+  await doc2.write({ title: 'Updated Test Document' });
+
+  console.log('After update:');
+  console.log(`  created_at: ${doc2.created_at.toISOString()}`);
+  console.log(`  updated_at: ${doc2.updated_at.toISOString()}`);
+  console.log('  (updated_at changed automatically)\n');
+
+  // Soft delete it
+  await doc2.unlink();
+
+  console.log('After soft delete:');
+  console.log(`  deleted_at: ${doc2.deleted_at?.toISOString()}`);
+  console.log(`  isDeleted: ${doc2.isDeleted}\n`);
+
+  console.log('=== Demo Complete ===');
+
+  await conn.destroy();
+}
+
+if (require.main === module) {
+  main().catch(console.error);
+}
+
+module.exports = main;

demo/mixins/models/Document.js

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+/**
+ * Document Model
+ * 
+ * Example model that uses both Timestampable and SoftDeletable mixins.
+ */
+class Document {
+  static _name = 'Document';
+  static table = 'documents';
+  static mixins = ['Timestampable', 'SoftDeletable'];
+
+  static fields = {
+    id: 'primary',
+    title: { type: 'string', required: true },
+    content: 'text',
+    author_id: { type: 'many-to-one', model: 'User' }
+  };
+}
+
+// Define name property to override readonly built-in
+Object.defineProperty(Document, 'name', {
+  value: 'Document',
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});
+
+module.exports = Document;

demo/mixins/models/SoftDeletable.js

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+/**
+ * SoftDeletable Mixin
+ * 
+ * Implements soft delete functionality by overriding the unlink() method.
+ * Records are marked as deleted instead of being removed from the database.
+ * Includes a default scope to hide soft-deleted records from queries.
+ */
+class SoftDeletable {
+  static _name = 'SoftDeletable';
+  static abstract = true;
+
+  static fields = {
+    deleted_at: { type: 'datetime', default: null }
+  };
+
+  // Use a default scope to hide soft-deleted records
+  static defaultScope = {
+    where: { deleted_at: null }
+  };
+
+  /**
+   * Override unlink to perform soft delete.
+   * Sets deleted_at timestamp instead of removing the record.
+   */
+  async unlink() {
+    if (this.deleted_at) {
+      // Already soft-deleted, perform hard delete
+      return await this.forceUnlink();
+    }
+
+    // Soft delete: just set deleted_at
+    await this.write({ deleted_at: new Date() });
+    return this;
+  }
+
+  /**
+   * Perform a hard delete (actually remove from database).
+   * This bypasses the soft delete mechanism.
+   */
+  async forceUnlink() {
+    // Call the original unlink implementation
+    const model = this._model;
+    if (!model) return this;
+
+    this._model = null;
+    await this.pre_unlink();
+    await this.pre_validate();
+
+    const pre_unlink = [];
+    for (const field of Object.values(model.fields)) {
+      pre_unlink.push(field.pre_unlink(this));
+    }
+    await Promise.all(pre_unlink);
+
+    // Delete from database
+    await model.query().where({ id: this.id }).delete();
+
+    if (this._parent) {
+      await this._parent.unlink();
+    }
+
+    // Run post hooks
+    await this.post_unlink();
+    const post_unlink = [];
+    for (const field of Object.values(model.fields)) {
+      post_unlink.push(field.post_unlink(this));
+    }
+    await Promise.all(post_unlink);
+
+    return this;
+  }
+
+  /**
+   * Restore a soft-deleted record by clearing deleted_at.
+   */
+  async restore() {
+    if (!this.deleted_at) {
+      throw new Error('Record is not deleted');
+    }
+    await this.write({ deleted_at: null });
+    return this;
+  }
+
+  /**
+   * Check if record is soft-deleted.
+   */
+  get isDeleted() {
+    return !!this.deleted_at;
+  }
+}
+
+// Define name property to override readonly built-in
+Object.defineProperty(SoftDeletable, 'name', {
+  value: 'SoftDeletable',
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});
+
+module.exports = SoftDeletable;

demo/mixins/models/Timestampable.js

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+/**
+ * Timestampable Mixin
+ * 
+ * Automatically manages created_at and updated_at fields.
+ * Include this mixin in any model that needs timestamp tracking.
+ */
+class Timestampable {
+  static _name = 'Timestampable';
+  static abstract = true;
+
+  static fields = {
+    created_at: { type: 'datetime', default: () => new Date() },
+    updated_at: { type: 'datetime', default: () => new Date() }
+  };
+
+  // Automatically update timestamp on record changes
+  async pre_update() {
+    this.updated_at = new Date();
+  }
+
+  async pre_create() {
+    const now = new Date();
+    if (!this.created_at) this.created_at = now;
+    if (!this.updated_at) this.updated_at = now;
+  }
+}
+
+// Define name property to override readonly built-in
+Object.defineProperty(Timestampable, 'name', {
+  value: 'Timestampable',
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});
+
+module.exports = Timestampable;