Chat Database

Last updated: January 26, 2026

Location: /inc/Core/Database/Chat/Chat.php

Since: v0.2.0 (Universal Engine Architecture)

Namespace: DataMachineCoreDatabaseChat

Table: wp_datamachine_chat_sessions

Overview

ChatDatabase provides comprehensive session management for the Chat API, handling CRUD operations, user isolation, and automatic session expiration. Supports persistent conversation storage with 24-hour session lifespans.

Purpose

Centralizes all database operations for chat sessions, enabling multi-turn conversations with conversation history persistence, user-scoped access control, and automatic cleanup of expired sessions.

Database Schema

Table Structure

Table Name: wp_datamachine_chat_sessions

Columns:

CREATE TABLE wp_datamachine_chat_sessions (
    session_id VARCHAR(50) NOT NULL,              -- UUID4 session identifier
    user_id BIGINT(20) UNSIGNED NOT NULL,         -- WordPress user ID
    messages LONGTEXT NOT NULL,                   -- JSON array of conversation messages
    metadata LONGTEXT NULL,                       -- JSON object for session metadata
    provider VARCHAR(50) NULL,                    -- AI provider (anthropic, openai, google, grok, openrouter)
    model VARCHAR(100) NULL,                      -- AI model identifier (e.g., claude-3-5-sonnet-20241022)
    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    expires_at DATETIME NULL,                     -- Auto-cleanup timestamp (24 hours from creation)
    PRIMARY KEY (session_id),
    KEY user_id (user_id),
    KEY created_at (created_at),
    KEY expires_at (expires_at)
);

Indexes:

Primary key on session_id for direct session lookup
Index on user_id for user-scoped queries
Index on created_at for chronological ordering
Index on expires_at for efficient cleanup queries

Character Set: Uses WordPress database charset and collation

Core Methods

Table Management

create_table()

Create chat sessions table using WordPress dbDelta for safe table creation/updates.

Signature:

public static function create_table(): void

Behavior:

Uses dbDelta() for safe table creation (handles existing tables)
Creates indexes for efficient querying
Logs table creation via datamachine_log action
Called during plugin activation

Example:

use DataMachineCoreDatabaseChatChat as ChatDatabase;

// During plugin activation
ChatDatabase::create_table();

Usage: Automatic during plugin activation, safe to call multiple times

table_exists()

Check if chat sessions table exists in database.

Signature:

public static function table_exists(): bool

Returns: True if table exists, false otherwise

Example:

if (ChatDatabase::table_exists()) {
    // Table ready for use
} else {
    ChatDatabase::create_table();
}

get_table_name()

Get full table name with WordPress prefix.

Signature:

public static function get_table_name(): string

Returns: Full table name (e.g., wp_datamachine_chat_sessions)

Example:

$table = ChatDatabase::get_table_name();
// Returns: "wp_datamachine_chat_sessions" (or custom prefix)

Session CRUD Operations

create_session()

Create new chat session for user.

Signature:

public function create_session(int $user_id, array $metadata = []): string

Parameters:

$user_id (int) – WordPress user ID
$metadata (array) – Optional session metadata (default: empty array)

Returns: Session ID (UUID4) or empty string on failure

Default Values:

session_id: Generated UUID4
messages: Empty JSON array ([])
metadata: JSON-encoded metadata array
provider: NULL
model: NULL
expires_at: 24 hours from creation time (GMT)

Example:

$chat_db = new ChatDatabase();

$session_id = $chat_db->create_session(
    get_current_user_id(),
    ['created_by' => 'chat_interface', 'version' => '1.0']
);

if ($session_id) {
    // Session created successfully
    // Use $session_id for subsequent operations
}

Logging:

Success: Debug log with session_id and user_id
Failure: Error log with user_id and database error

get_session()

Retrieve session data with automatic expiration checking.

Signature:

public function get_session(string $session_id): ?array

Parameters:

$session_id (string) – Session UUID

Returns: Session data array or null if not found/expired

Returned Array Structure:

[
    'session_id' => 'uuid-string',
    'user_id' => 123,
    'messages' => [  // Decoded from JSON
        ['role' => 'user', 'content' => 'Hello'],
        ['role' => 'assistant', 'content' => 'Hi there!']
    ],
    'metadata' => [  // Decoded from JSON
        'message_count' => 2,
        'last_activity' => '2024-01-01 12:00:00'
    ],
    'provider' => 'anthropic',
    'model' => 'claude-3-5-sonnet-20241022',
    'created_at' => '2024-01-01 10:00:00',
    'updated_at' => '2024-01-01 12:00:00',
    'expires_at' => '2024-01-02 10:00:00'
]

Expiration Handling:

Checks expires_at timestamp against current time
Automatically deletes expired sessions
Returns null for expired sessions

JSON Decoding:

messages field decoded to PHP array
metadata field decoded to PHP array
Invalid JSON defaults to empty array

Example:

$chat_db = new ChatDatabase();

$session = $chat_db->get_session('uuid-abc-123');

if ($session) {
    $messages = $session['messages'];
    $user_id = $session['user_id'];
    // Continue conversation
} else {
    // Session not found or expired
    // Create new session
}

Security: No user isolation check in this method – caller must verify user_id matches current user

update_session()

Update session with new messages and metadata.

Signature:

public function update_session(
    string $session_id,
    array $messages,
    array $metadata = [],
    string $provider = '',
    string $model = ''
): bool

Parameters:

$session_id (string) – Session UUID
$messages (array) – Complete messages array (replaces existing)
$metadata (array) – Updated metadata (replaces existing)
$provider (string) – AI provider (optional, only updated if non-empty)
$model (string) – AI model (optional, only updated if non-empty)

Returns: True on success, false on failure

Update Behavior:

messages: Always replaced with provided array (JSON-encoded)
metadata: Always replaced with provided array (JSON-encoded)
provider: Only updated if non-empty string provided
model: Only updated if non-empty string provided
updated_at: Automatically updated by database

Example:

$chat_db = new ChatDatabase();

// Get current session
$session = $chat_db->get_session('uuid-abc-123');

// Add new message to conversation
$messages = $session['messages'];
$messages[] = ['role' => 'user', 'content' => 'New message'];

// Update metadata
$metadata = $session['metadata'];
$metadata['message_count'] = count($messages);
$metadata['last_activity'] = gmdate('Y-m-d H:i:s');

// Save updates
$success = $chat_db->update_session(
    'uuid-abc-123',
    $messages,
    $metadata,
    'anthropic',
    'claude-sonnet-4'
);

Logging:

Failure: Error log with session_id and database error

Important: Caller must retrieve existing messages/metadata and merge changes – this method replaces entire arrays

delete_session()

Delete session from database.

Signature:

public function delete_session(string $session_id): bool

Parameters:

$session_id (string) – Session UUID

Returns: True on success, false on failure

Example:

$chat_db = new ChatDatabase();

$deleted = $chat_db->delete_session('uuid-abc-123');

if ($deleted) {
    // Session deleted successfully
}

Logging:

Success: Debug log with session_id
Failure: Error log with session_id and database error

Usage:

Manual session termination
Automatic expiration cleanup (called by get_session)
User logout cleanup

Maintenance

cleanup_expired_sessions()

Cleanup all expired sessions from database.

Signature:

public function cleanup_expired_sessions(): int

Returns: Number of deleted sessions

Cleanup Logic:

Deletes sessions where expires_at IS NOT NULL AND expires_at < NOW()
Uses GMT time for comparison
Batch deletion for efficiency

Example:

$chat_db = new ChatDatabase();

$deleted_count = $chat_db->cleanup_expired_sessions();

// Result: 15 expired sessions deleted

Logging:

Logs info message if any sessions deleted (includes count)

Recommended Schedule: Run via WordPress cron job (hourly or daily)

Cron Setup Example:

// Register cron event
add_action('init', function() {
    if (!wp_next_scheduled('datamachine_cleanup_chat_sessions')) {
        wp_schedule_event(time(), 'hourly', 'datamachine_cleanup_chat_sessions');
    }
});

// Hook cleanup function
add_action('datamachine_cleanup_chat_sessions', function() {
    $chat_db = new DataMachineCoreDatabaseChatChat();
    $chat_db->cleanup_expired_sessions();
});

Integration with Chat API

Chat Endpoint Usage

The Chat API endpoint (/inc/Api/Chat/Chat.php) uses ChatDatabase for session management:

Session Creation:

// First message (no session_id provided)
$chat_db = new ChatDatabase();
$session_id = $chat_db->create_session(get_current_user_id());

Session Retrieval:

// Subsequent messages (session_id provided)
$session = $chat_db->get_session($session_id);

// Verify user ownership
if ($session['user_id'] !== get_current_user_id()) {
    return new WP_Error('session_access_denied', 'Access denied to this session', ['status' => 403]);
}

Session Update:

// After AI response
$messages = $session['messages'];
$messages[] = ['role' => 'user', 'content' => $user_message];
$messages[] = ['role' => 'assistant', 'content' => $ai_response];

$metadata = [
    'message_count' => count($messages),
    'last_activity' => gmdate('Y-m-d H:i:s')
];

$chat_db->update_session($session_id, $messages, $metadata, $provider, $model);

Security Features

User Isolation

Sessions are scoped to individual WordPress users:

Creation: Requires valid user_id
Access: Caller must verify session user_id matches current user
No Cross-User Access: Database queries don’t enforce this – API layer responsibility

Security Check Pattern:

$session = $chat_db->get_session($session_id);

if (!$session) {
    return new WP_Error('session_not_found', 'Session not found or expired', ['status' => 404]);
}

if ($session['user_id'] !== get_current_user_id()) {
    return new WP_Error('session_access_denied', 'Access denied to this session', ['status' => 403]);
}

Automatic Expiration

Sessions automatically expire after 24 hours:

Expiration Time: Set to NOW() + 24 hours at creation
Cleanup: Automatic via get_session() and manual via cleanup_expired_sessions()
Purpose: Prevent stale session accumulation

Data Storage Patterns

Messages Array

Structure:

[
    ['role' => 'user', 'content' => 'First user message'],
    ['role' => 'assistant', 'content' => 'AI response', 'tool_calls' => [...]],
    ['role' => 'user', 'content' => 'TOOL RESPONSE: ...'],
    ['role' => 'assistant', 'content' => 'Final response']
]

Storage: JSON-encoded LONGTEXT
Retrieval: JSON-decoded to PHP array
Validation: Invalid JSON defaults to empty array

Metadata Object

Common Fields:

[
    'message_count' => 10,
    'last_activity' => '2024-01-01 12:00:00',
    'created_by' => 'chat_interface',
    'version' => '1.0',
    'custom_field' => 'custom_value'
]

Storage: JSON-encoded LONGTEXT
Flexibility: Arbitrary key-value pairs allowed
Retrieval: JSON-decoded to PHP array

Provider and Model Tracking

Purpose: Track which AI provider/model used for conversation
Updates: Set during first AI call, can be updated on subsequent calls
Nullable: Can be NULL if not yet set

Performance Considerations

Indexes

Optimized for common query patterns:

session_id (PRIMARY): Direct session lookup (O(1))
user_id: User session queries
created_at: Chronological ordering
expires_at: Efficient cleanup queries

JSON Storage

Benefits:

Flexible message structure
No schema changes needed for metadata additions
Efficient storage for variable-length arrays

Considerations:

JSON decoding overhead (minimal for chat usage)
Not indexed (full messages not searchable)
Acceptable for conversation-scoped queries

Usage Examples

Complete Session Lifecycle

use DataMachineCoreDatabaseChatChat as ChatDatabase;

$chat_db = new ChatDatabase();
$user_id = get_current_user_id();

// 1. Create new session
$session_id = $chat_db->create_session($user_id, [
    'created_by' => 'rest_api',
    'version' => '1.0'
]);

// 2. First message exchange
$messages = [
    ['role' => 'user', 'content' => 'Create a pipeline']
];

$chat_db->update_session($session_id, $messages, [
    'message_count' => 1,
    'last_activity' => gmdate('Y-m-d H:i:s')
]);

// 3. Continue conversation
$session = $chat_db->get_session($session_id);
$messages = $session['messages'];
$messages[] = ['role' => 'assistant', 'content' => 'I'll create a pipeline for you...'];

$chat_db->update_session($session_id, $messages, [
    'message_count' => count($messages),
    'last_activity' => gmdate('Y-m-d H:i:s')
], 'anthropic', 'claude-sonnet-4');

// 4. Session expires automatically after 24 hours
// Or manual cleanup:
$chat_db->cleanup_expired_sessions();

User Session Management

// Get all user sessions (custom query)
global $wpdb;
$table = ChatDatabase::get_table_name();

$user_sessions = $wpdb->get_results($wpdb->prepare(
    "SELECT session_id, created_at, updated_at FROM {$table}
     WHERE user_id = %d AND expires_at > %s
     ORDER BY updated_at DESC",
    get_current_user_id(),
    current_time('mysql', true)
), ARRAY_A);

// Display active sessions to user
foreach ($user_sessions as $session_info) {
    echo "Session: {$session_info['session_id']} (Updated: {$session_info['updated_at']})n";
}

Related Components

Chat API Endpoint – REST API using ChatDatabase
AIConversationLoop – Conversation execution
Universal Engine Architecture – Shared AI infrastructure
Database Schema – Complete database documentation

Location: /inc/Core/Database/Chat/Chat.php
Namespace: DataMachineCoreDatabaseChat
Table: wp_datamachine_chat_sessions
Since: v0.2.0

Chat Database

Overview

Purpose

Database Schema

Table Structure

Core Methods

Table Management

create_table()

table_exists()

get_table_name()

Session CRUD Operations

create_session()

get_session()

update_session()

delete_session()

Maintenance

cleanup_expired_sessions()

Integration with Chat API

Chat Endpoint Usage

Security Features

User Isolation

Automatic Expiration

Data Storage Patterns

Messages Array

Metadata Object

Provider and Model Tracking

Performance Considerations

Indexes

JSON Storage

Usage Examples

Complete Session Lifecycle

User Session Management

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