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+# Run Instructions: QueryBuilder
+
+## 1. Overview
+
+**QueryBuilder** (`abdulelahragih/querybuilder`) is a fast, lightweight, zero-dependency SQL query builder for PHP 8.1+. The syntax is inspired by the Laravel Query Builder, providing an expressive and fluent interface for building SQL statements while relying strictly on native PHP PDO (`ext-pdo`) for secure, parameterized query execution.
+
+### Architectural Highlights & Role
+- **Type**: PHP Library / Composer Package (not a standalone web server or daemon).
+- **Core Engine**: `Abdulelahragih\QueryBuilder\QueryBuilder` handles statement composition, binding parameters, and dispatching execution to PDO.
+- **Dialect Abstraction**: Includes built-in support for dialect-specific syntax for **MySQL** (`MySqlDialect`) and **PostgreSQL** (`PostgresDialect`), with automatic dialect detection based on the active `PDO::ATTR_DRIVER_NAME`.
+- **Grammar & Statements**: Modular clause abstractions (`SelectStatement`, `InsertStatement`, `UpdateStatement`, `DeleteStatement`, `WhereClause`, `JoinClause`, `OnConflictClause`).
+- **Data Collections**: Query results are returned wrapped in custom fluent `Collection` objects (`Abdulelahragih\QueryBuilder\Data\Collection`) with helper methods (`map`, `filter`, `pluck`, `chunk`, `sorted`, etc.).
+- **Pagination Support**: Provides both length-aware (`LengthAwarePaginator`) and lightweight simple pagination (`SimplePaginator`).
+- **Facades & Helpers**: Includes an instance-based wrapper (`DB`) and a static facade (`DBSingleton`) with automatic transaction management.
+- **Safety First**: Implements safeguards such as forbidding `UPDATE` or `DELETE` operations without a `WHERE` clause unless explicitly configured, throwing `QueryBuilderException`.
+
+---
+
+## 2. Prerequisites
+
+### Runtime & Core Tools
+- **PHP**: Version `^8.1` (tested with PHP 8.1 up to PHP 8.3+)
+  - Verify with: `php -v`
+- **PHP Extensions**:
+  - `pdo` (Required core extension for runtime execution and parameter binding)
+  - `pdo_sqlite` (Required for running the local PHPUnit test suite with in-memory SQLite)
+  - `pdo_mysql` / `pdo_pgsql` (Optional runtime drivers when connecting consuming applications to MySQL or PostgreSQL)
+  - Verify with: `php -m | grep -i pdo`
+- **Composer**: Composer v2.x
+  - Verify with: `composer -V`
+
+### Database / External Services
+- **Local Development & Testing**: No external database service (MySQL, PostgreSQL, etc.) is required to run the development test suite. Tests execute against an in-memory SQLite instance (`sqlite::memory:`).
+- **Target Databases (Production / Staging / Integration)**:
+  - MySQL 5.7+ / 8.0+
+  - PostgreSQL 12+
+
+---
+
+## 3. Environment & Configuration
+
+Because **QueryBuilder** is an embeddable PHP library rather than a standalone application, it does not rely on `.env` files or external secret managers.
+
+### Configuration Model
+- Database connections are configured programmatically at runtime by the consuming host application by passing an initialized `\PDO` instance to `new QueryBuilder($pdo)` or `DBSingleton::init($pdo)`.
+- Test configuration is governed by [`phpunit.xml`](phpunit.xml), which defines the test suite paths, source code coverage directories, and sets `PHPUNIT_TEST_SUITE=1`.
+
+---
+
+## 4. Installation & Setup
+
+### For Local Development and Contributing
+
+1. **Clone the repository and enter the directory**:
+   ```bash
+   git clone <repo-url> QueryBuilder
+   cd QueryBuilder
+   ```
+
+2. **Validate Composer file integrity**:
+   ```bash
+   composer validate
+   ```
+
+3. **Install development dependencies**:
+   ```bash
+   composer install
+   ```
+
+### For Consuming Projects
+
+To use this library inside another PHP project, add it via Composer:
+
+```bash
+composer require abdulelahragih/querybuilder
+```
+
+---
+
+## 5. Running the Application
+
+As a library, QueryBuilder does not expose an HTTP server or long-running daemon. It is consumed within PHP scripts, CLI commands, or web applications.
+
+### Quick Verification via PHP CLI
+
+You can verify that the library and Composer autoloading work properly using an interactive or one-line PHP script with an in-memory SQLite database:
+
+```bash
+php -r '
+require __DIR__ . "/vendor/autoload.php";
+
+use Abdulelahragih\QueryBuilder\QueryBuilder;
+
+// Create an in-memory SQLite PDO instance
+$pdo = new PDO("sqlite::memory:");
+$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
+
+// Create sample schema
+$pdo->exec("CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT);");
+
+// Initialize QueryBuilder
+$qb = new QueryBuilder($pdo);
+
+// Insert records
+$qb->table("users")->insert([
+    ["id" => 1, "name" => "Alice"],
+    ["id" => 2, "name" => "Bob"]
+]);
+
+// Query records
+$users = $qb->table("users")->where("id", "=", 1)->get();
+echo "Found user: " . $users->first()["name"] . PHP_EOL;
+'
+```
+
+### Usage Examples in Application Code
+
+#### 1. Basic Querying with `QueryBuilder`
+```php
+use Abdulelahragih\QueryBuilder\QueryBuilder;
+
+$pdo = new PDO("mysql:host=127.0.0.1;dbname=app_db;charset=utf8mb4", "user", "password");
+$qb = new QueryBuilder($pdo);
+
+// Select query
+$users = $qb->table("users")
+    ->select("id", "name", "email")
+    ->where("status", "=", "active")
+    ->orderBy("created_at", "DESC")
+    ->limit(10)
+    ->get(); // Returns Abdulelahragih\QueryBuilder\Data\Collection
+```
+
+#### 2. Using the Static Facade (`DBSingleton`)
+```php
+use Abdulelahragih\QueryBuilder\DBSingleton;
+
+DBSingleton::init($pdo);
+
+$activeCount = DBSingleton::table("users")
+    ->where("active", "=", 1)
+    ->count();
+
+$user = DBSingleton::table("users")->where("id", "=", 10)->first();
+```
+
+#### 3. Upsert Operations (Dialect-Aware)
+```php
+use Abdulelahragih\QueryBuilder\Grammar\Expression;
+
+// Upsert supports MySQL ON DUPLICATE KEY UPDATE and PostgreSQL ON CONFLICT DO UPDATE
+$qb->table("users")->upsert(
+    ["id" => 100, "name" => "John", "age" => 26],
+    uniqueBy: ["id"],
+    updateOnDuplicate: [
+        "name",
+        "updated_at" => Expression::make("NOW()"),
+    ]
+);
+```
+
+#### 4. Pagination
+```php
+// Length-aware paginator (calculates total count and pages)
+$paginator = $qb->table("users")
+    ->where("role", "=", "member")
+    ->paginate(page: 1, perPage: 15);
+
+$total = $paginator->total();
+$items = $paginator->items();
+$hasMore = $paginator->hasMorePages();
+```
+
+---
+
+## 6. Testing & Verification
+
+### Running Automated Unit Tests
+
+QueryBuilder comes with a comprehensive PHPUnit test suite validating SQL compilation, dialect nuances, edge cases, collections, pagination, and error handling.
+
+1. **Run standard test suite**:
+   ```bash
+   composer test
+   ```
+
+2. **Run all tests (via Composer alias)**:
+   ```bash
+   composer test:all
+   ```
+
+3. **Run directly using PHPUnit binary**:
+   ```bash
+   ./vendor/bin/phpunit
+   ```
+
+4. **Run a specific test suite or test case**:
+   ```bash
+   ./vendor/bin/phpunit tests/MysqlDialectTest.php
+   ./vendor/bin/phpunit tests/PostgresQueryBuilderTest.php
+   ./vendor/bin/phpunit --filter testSimpleSelect
+   ```
+
+### Expected Output
+All 205+ tests should pass with 0 failures and 0 errors:
+```text
+OK (205 tests, 365 assertions)
+```
+
+---
+
+## 7. Troubleshooting & FAQ
+
+### 1. `Class "PDO" not found` or driver missing
+- **Cause**: PHP was compiled or installed without PDO extensions enabled.
+- **Resolution**:
+  - macOS (Homebrew): `brew install php` (includes default PDO extensions).
+  - Ubuntu/Debian: `sudo apt-get install php-pdo php-sqlite3 php-mysql php-pgsql`
+  - Ensure extension lines (`extension=pdo`, `extension=pdo_sqlite`) are uncommented in `php.ini`.
+
+### 2. `QueryBuilderException: UPDATE or DELETE without WHERE clause is not allowed`
+- **Cause**: An `update()` or `delete()` operation was invoked without defining condition clauses. This is an intentional safeguard to prevent accidental data truncation.
+- **Resolution**: Ensure you chain a `.where(...)` condition before calling `update()` or `delete()`.
+
+### 3. `InvalidArgumentException: Upsert is not supported by this dialect`
+- **Cause**: Using an unsupported database dialect with `upsert()` or `insertOrIgnore()`.
+- **Resolution**: Upserts currently support MySQL (`MySqlDialect`) and PostgreSQL (`PostgresDialect`). Ensure your PDO connection driver is either `mysql` or `pgsql`, or supply the dialect explicitly:
+  ```php
+  use Abdulelahragih\QueryBuilder\Grammar\Dialects\PostgresDialect;
+
+  $qb = new QueryBuilder($pdo, new PostgresDialect());
+  ```
+
+### 4. Tests fail with cache error
+- **Cause**: PHPUnit cache directory write permission issues.
+- **Resolution**: Run `composer test` which passes `--do-not-cache-result`, or delete the `.phpunit.cache` directory:
+  ```bash
+  rm -rf .phpunit.cache .phpunit.result.cache
+  ```