Database Engine and Connection

def create_engine(
    url: Union[str, URL],
    *,
    connect_args: Optional[Dict[str, Any]] = None,
    echo: bool = False,
    echo_pool: bool = False,
    enable_from_linting: bool = True,
    hide_parameters: bool = False,
    insertmanyvalues_page_size: int = 1000,
    isolation_level: Optional[str] = None,
    json_deserializer: Optional[Callable] = None,
    json_serializer: Optional[Callable] = None,
    label_length: Optional[int] = None,
    logging_name: Optional[str] = None,
    max_identifier_length: Optional[int] = None,
    max_overflow: int = 10,
    module: Optional[Any] = None,
    paramstyle: Optional[str] = None,
    pool: Optional[Pool] = None,
    poolclass: Optional[Type[Pool]] = None,
    pool_logging_name: Optional[str] = None,
    pool_pre_ping: bool = False,
    pool_recycle: int = -1,
    pool_reset_on_return: Optional[str] = None,
    pool_size: int = 5,
    pool_timeout: float = 30.0,
    plugins: Optional[List[str]] = None,
    query_cache_size: int = 500,
    **kwargs: Any
) -> Engine:
    """
    Create a database engine for connecting to databases.
    
    Parameters:
        url: Database URL (e.g., "sqlite:///database.db", "postgresql://user:pass@host/db")
        connect_args: Additional arguments passed to the database driver
        echo: Whether to log all SQL statements (useful for debugging)
        echo_pool: Whether to log connection pool events
        pool_size: Number of connections to maintain in the pool
        max_overflow: Additional connections beyond pool_size
        pool_timeout: Seconds to wait for connection from pool
        pool_recycle: Seconds after which connection is recreated
        pool_pre_ping: Validate connections before use
        isolation_level: Transaction isolation level
        
    Returns:
        Engine object for database operations
    """

def create_mock_engine(dialect: str, executor: Callable) -> MockConnection:
    """
    Create a mock engine for testing without a real database.
    
    Parameters:
        dialect: SQL dialect to mock
        executor: Function to handle SQL execution
        
    Returns:
        MockConnection for testing purposes
    """

def engine_from_config(
    configuration: Dict[str, Any],
    prefix: str = "sqlalchemy.",
    **kwargs: Any
) -> Engine:
    """
    Create an engine from a configuration dictionary.
    
    Parameters:
        configuration: Dictionary with engine configuration
        prefix: Prefix for configuration keys
        **kwargs: Additional engine arguments
        
    Returns:
        Engine configured from the dictionary
    """

# SQLite engine (file-based)
engine = create_engine("sqlite:///heroes.db", echo=True)

# PostgreSQL engine
engine = create_engine(
    "postgresql://user:password@localhost/heroes",
    pool_size=20,
    max_overflow=0,
    pool_recycle=3600
)

# MySQL engine with connection arguments
engine = create_engine(
    "mysql+pymysql://user:password@localhost/heroes",
    connect_args={"charset": "utf8mb4"},
    echo=False
)

# In-memory SQLite for testing
engine = create_engine("sqlite:///:memory:", echo=True)

# Engine from configuration
config = {
    "sqlalchemy.url": "sqlite:///heroes.db",
    "sqlalchemy.echo": "true",
    "sqlalchemy.pool_size": "10"
}
engine = engine_from_config(config)

class QueuePool(Pool):
    """
    Queue-based connection pool (default for most databases).
    
    Maintains a fixed-size pool of connections with overflow capability.
    Connections are distributed on a FIFO basis.
    """

class StaticPool(Pool):
    """
    Static connection pool that maintains a single connection.
    
    Useful for in-memory databases or single-connection scenarios.
    All operations share the same connection.
    """

# Explicit pool configuration
from sqlalchemy.pool import QueuePool, StaticPool

# Custom queue pool
engine = create_engine(
    "postgresql://user:pass@host/db",
    poolclass=QueuePool,
    pool_size=10,
    max_overflow=20,
    pool_pre_ping=True
)

# Static pool for SQLite
engine = create_engine(
    "sqlite:///database.db",
    poolclass=StaticPool,
    connect_args={"check_same_thread": False}
)

def inspect(bind: Union[Engine, Connection]) -> Inspector:
    """
    Create an Inspector for examining database structure.
    
    Parameters:
        bind: Engine or Connection to inspect
        
    Returns:
        Inspector object for schema reflection
    """

# Inspect database schema
inspector = inspect(engine)

# Get table names
table_names = inspector.get_table_names()
print("Tables:", table_names)

# Get column information
columns = inspector.get_columns("heroes")
for column in columns:
    print(f"Column: {column['name']}, Type: {column['type']}")

# Get foreign keys
foreign_keys = inspector.get_foreign_keys("heroes")
for fk in foreign_keys:
    print(f"FK: {fk['constrained_columns']} -> {fk['referred_table']}.{fk['referred_columns']}")

# Check if table exists
if inspector.has_table("heroes"):
    print("Heroes table exists")

from sqlmodel import SQLModel, Field, Session, create_engine, select
from typing import Optional

# Define model
class Hero(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str
    secret_name: str
    age: Optional[int] = None

# Create engine
engine = create_engine("sqlite:///heroes.db", echo=True)

# Create tables
SQLModel.metadata.create_all(engine)

# Use with sessions
def create_hero(name: str, secret_name: str, age: Optional[int] = None) -> Hero:
    hero = Hero(name=name, secret_name=secret_name, age=age)
    with Session(engine) as session:
        session.add(hero)
        session.commit()
        session.refresh(hero)
        return hero

def get_heroes() -> List[Hero]:
    with Session(engine) as session:
        statement = select(Hero)
        heroes = session.exec(statement).all()
        return heroes

# Usage
hero = create_hero("Spider-Boy", "Pedro Parqueador", 16)
all_heroes = get_heroes()

# Production PostgreSQL setup
engine = create_engine(
    "postgresql://user:password@host:5432/database",
    # Connection pool settings
    pool_size=20,          # Base number of connections
    max_overflow=30,       # Additional connections when needed
    pool_recycle=3600,     # Recreate connections after 1 hour
    pool_pre_ping=True,    # Validate connections before use
    
    # Performance settings
    echo=False,            # Disable SQL logging
    query_cache_size=1000, # Increase query cache
    
    # Connection arguments
    connect_args={
        "sslmode": "require",
        "connect_timeout": 10,
        "application_name": "my_app"
    }
)

# Development SQLite setup
engine = create_engine(
    "sqlite:///dev_database.db",
    echo=True,  # Enable SQL logging for debugging
    connect_args={"check_same_thread": False}  # Allow multiple threads
)

# In-memory database for tests
test_engine = create_engine(
    "sqlite:///:memory:",
    echo=False,
    poolclass=StaticPool,
    connect_args={"check_same_thread": False}
)