modelmirror 0.1.19

Model Mirror

ModelMirror

A Python library for automatic configuration management using JSON files. It lets you describe object instances and their dependencies in JSON, then automatically creates and connects those objects for you.

Key Features

• Non-Intrusive: Works with existing classes without modification
• Simple Registration: Just create a registry entry linking schema to class
• JSON Configuration: Human-readable configuration files
• Automatic Dependency Injection: Reference instances with $name syntax
• Singleton Management: Reuse instances across your configuration
• Type Safety: Optional Pydantic integration for type checking
• Dependency Resolution: Automatic topological sorting of dependencies

Tutorial 1: Quick Start - Your First Working Example

Let's create a simple example with two classes: a DatabaseService and a UserService that depends on it.

Step 1: Define Your Classes

# Your existing classes - no modifications required
class DatabaseService:
    def __init__(self, host: str, port: int):
        self.host = host
        self.port = port

    def connect(self):
        return f"Connected to {self.host}:{self.port}"

class UserService:
    def __init__(self, db: DatabaseService, cache_enabled: bool):
        self.db = db
        self.cache_enabled = cache_enabled

    def get_user(self, user_id: int):
        connection = self.db.connect()
        return f"User {user_id} from {connection} (cache: {self.cache_enabled})"

Step 2: Register Your Classes

Create registry entries that link your classes to schema identifiers:

from modelmirror.class_provider.class_register import ClassRegister
from modelmirror.class_provider.class_reference import ClassReference

# Register DatabaseService with id "database"
class DatabaseServiceRegister(ClassRegister,
    reference=ClassReference(id="database", cls=DatabaseService)):
    pass

# Register UserService with id "user_service"
class UserServiceRegister(ClassRegister,
    reference=ClassReference(id="user_service", cls=UserService)):
    pass

Step 3: Create JSON Configuration

Create a config.json file that defines your instances:

{
    "my_database": {
        "$mirror": "database:db_singleton",
        "host": "localhost",
        "port": 5432
    },
    "my_user_service": {
        "$mirror": "user_service",
        "db": "$db_singleton",
        "cache_enabled": true
    }
}

Step 4: Load and Use

from modelmirror.mirror import Mirror

# Load configuration
mirror = Mirror('myapp')  # 'myapp' is the package where your registers are defined
instances = mirror.reflect_raw('config.json')

# Get your configured instances
user_service = instances.get(UserService)
print(user_service.get_user(123))  # Output: User 123 from Connected to localhost:5432 (cache: True)

That's it! Your classes are now configured via JSON with automatic dependency injection.

Tutorial 2: Type-Safe Configuration with Pydantic

For production applications, add type safety with Pydantic schemas. Just add your schema definition:

from pydantic import BaseModel, ConfigDict

class AppConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)

    my_database: DatabaseService
    my_user_service: UserService

# Load with full type checking and IDE support
config = mirror.reflect('config.json', AppConfig)
print(config.my_database.host)  # Full autocomplete!

Tutorial 3: Understanding References - The Heart of ModelMirror

ModelMirror's power comes from its reference system. The $mirror field is what transforms JSON objects into live instances.

How $mirror Works

The $mirror field uses a simple string format that ModelMirror parses to understand:

1. Which class to instantiate (the registered ID)
2. Whether to create a singleton (optional instance name)

Format: "class_id" or "class_id:instance_name"

Basic Reference Structure

Every object you want to mirror needs a $mirror field:

{
    "my_service": {
        "$mirror": "service",
        "name": "My Service"
    }
}

What happens:

1. ModelMirror finds the class registered with ID "service"
2. Creates a new instance: ServiceClass(name="My Service")
3. Returns the configured object

Singleton References - Reuse Instances Anywhere

Add :instance_name to create a reusable singleton:

{
    "database": {
        "$mirror": "database:main_db",
        "host": "localhost",
        "port": 5432
    },
    "user_service": {
        "$mirror": "user_service",
        "database": "$main_db"
    },
    "admin_service": {
        "$mirror": "admin_service",
        "database": "$main_db"
    }
}

What happens:

1. "database:main_db" creates a singleton named "main_db"
2. "$main_db" references inject the same database instance
3. Both services share the exact same database object

Reference Parser Architecture

ModelMirror uses a pluggable parser system to handle $mirror strings:

from modelmirror.parser.reference_parser import ReferenceParser
from modelmirror.parser.default_reference_parser import DefaultReferenceParser

# Default parser handles: "id" and "id:instance"
default_parser = DefaultReferenceParser()

# You can create custom parsers for different formats
class CustomReferenceParser(ReferenceParser):
    def _parse(self, reference: str):
        # Your custom parsing logic
        pass

# Use custom parser
mirror = Mirror('myapp', reference_parser=CustomReferenceParser())

Built-in Parser Features:

• Simple format: "service" → creates new instance
• Singleton format: "service:name" → creates/reuses singleton
• Validation: Ensures reference strings are valid
• Extensible: Easy to add new reference formats

Reference Resolution Process

ModelMirror processes references in a specific order:

1. Parse: DefaultReferenceParser converts "database:main_db" to ParsedReference(id="database", instance="main_db")
2. Lookup: Find the class registered with ID "database"
3. Dependency Analysis: Scan for $singleton_name references in parameters
4. Topological Sort: Order instances to resolve dependencies first
5. Instantiate: Create objects with resolved dependencies
6. Singleton Management: Store named instances for reuse

Pydantic Schema for Type Safety

from pydantic import BaseModel, ConfigDict

class ServiceConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)

    database: DatabaseService
    user_service: UserService
    admin_service: AdminService

config = mirror.reflect('config.json', ServiceConfig)
# Full IDE support and validation!

Tutorial 4: Working with Collections

ModelMirror handles lists and dictionaries seamlessly.

Lists of Services

{
    "primary_db": {
        "$mirror": "database:primary",
        "host": "primary.db.com",
        "port": 5432
    },
    "services": [
        {
            "$mirror": "service",
            "name": "Service 1",
            "database": "$primary"
        },
        {
            "$mirror": "service",
            "name": "Service 2",
            "database": "$primary"
        }
    ]
}

Pydantic Schema for Lists

from typing import List
from pydantic import BaseModel, ConfigDict

class MultiServiceConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)

    primary_db: DatabaseService
    services: List[UserService]

config = mirror.reflect('config.json', MultiServiceConfig)
print(f"Loaded {len(config.services)} services")

Dictionaries of Services

{
    "databases": {
        "primary": {
            "$mirror": "database:primary_db",
            "host": "primary.db.com",
            "port": 5432
        },
        "secondary": {
            "$mirror": "database:secondary_db",
            "host": "secondary.db.com",
            "port": 5432
        }
    },
    "load_balancer": {
        "$mirror": "load_balancer",
        "primary_db": "$primary_db",
        "secondary_db": "$secondary_db"
    }
}

Pydantic Schema for Dictionaries

from typing import Dict
from pydantic import BaseModel, ConfigDict

class DatabaseClusterConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)

    databases: Dict[str, DatabaseService]
    load_balancer: LoadBalancerService

config = mirror.reflect('config.json', DatabaseClusterConfig)
print(f"Primary DB: {config.databases['primary'].host}")

Tutorial 5: Nested Structures and Complex Dependencies

ModelMirror handles deeply nested configurations effortlessly.

Multi-Level Dependencies

{
    "cache": {
        "$mirror": "cache:redis_cache",
        "host": "redis.internal",
        "port": 6379
    },
    "database": {
        "$mirror": "database:postgres_db",
        "host": "postgres.internal",
        "port": 5432
    },
    "user_service": {
        "$mirror": "user_service:user_svc",
        "database": "$postgres_db",
        "cache": "$redis_cache"
    },
    "notification_service": {
        "$mirror": "notification_service",
        "user_service": "$user_svc",
        "templates": {
            "email": "Welcome {{name}}!",
            "sms": "Hi {{name}}, welcome!"
        }
    }
}

Pydantic Schema for Complex Apps

from typing import Dict
from pydantic import BaseModel, ConfigDict

class AppConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)

    cache: CacheService
    database: DatabaseService
    user_service: UserService
    notification_service: NotificationService

config = mirror.reflect('config.json', AppConfig)
# ModelMirror automatically resolves all dependencies in correct order!

Nested Objects and Arrays

{
    "microservices": {
        "auth": {
            "$mirror": "auth_service:auth",
            "jwt_secret": "secret123",
            "token_expiry": 3600
        },
        "api_gateway": {
            "$mirror": "gateway",
            "auth_service": "$auth",
            "routes": [
                {
                    "path": "/users",
                    "service": "$user_svc",
                    "methods": ["GET", "POST"]
                },
                {
                    "path": "/notifications",
                    "service": "$notification_svc",
                    "methods": ["POST"]
                }
            ]
        }
    }
}

Tutorial 6: Validation and Error Handling

Use Pydantic's powerful validation to catch configuration errors early.

Strict Validation

from pydantic import BaseModel, Field, ConfigDict
from typing import List

class DatabaseConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True, extra='forbid')

    host: str = Field(min_length=1, description="Database hostname")
    port: int = Field(ge=1, le=65535, description="Database port")
    max_connections: int = Field(ge=1, le=1000, default=10)
    ssl_enabled: bool = Field(default=True)

class ServiceConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)

    name: str = Field(min_length=1, max_length=50)
    timeout: int = Field(ge=1, le=300, default=30)
    retries: int = Field(ge=0, le=10, default=3)

class AppConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)

    database: DatabaseService
    services: List[ServiceConfig]
    debug_mode: bool = Field(default=False)

# This will validate all constraints when loading
config = mirror.reflect('config.json', AppConfig)

Optional Fields and Defaults

from typing import Optional
from pydantic import BaseModel, ConfigDict

class FlexibleConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)

    required_service: DatabaseService
    optional_cache: Optional[CacheService] = None
    debug_enabled: bool = False
    max_retries: int = 3

# JSON can omit optional fields
config = mirror.reflect('minimal_config.json', FlexibleConfig)

Advanced: Mirror Customization

Custom Reference Parsers

Create custom parsers for specialized reference formats:

from modelmirror.parser.reference_parser import ReferenceParser, ParsedReference, FormatValidation

class VersionedReferenceParser(ReferenceParser):
    """Supports format: service@v1.0:instance_name"""

    def _validate(self, reference: str) -> FormatValidation:
        if '@' not in reference:
            return FormatValidation(False, "Missing version: use format 'id@version' or 'id@version:instance'")
        return FormatValidation(True)

    def _parse(self, reference: str) -> ParsedReference:
        if ':' in reference:
            id_version, instance = reference.split(':', 1)
        else:
            id_version, instance = reference, None

        id_part, version = id_version.split('@', 1)
        # You could use version for class selection logic
        return ParsedReference(id=id_part, instance=instance)

# Use your custom parser
mirror = Mirror('myapp', parser=VersionedReferenceParser())

Custom Placeholders

Change the placeholder field from $mirror to anything you prefer:

# Use $ref instead of $mirror
mirror = Mirror('myapp', placeholder='$ref')

# Use $create for a more descriptive name
mirror = Mirror('myapp', placeholder='$create')

# Use $service for domain-specific naming
mirror = Mirror('myapp', placeholder='$service')

JSON with custom placeholder:

{
    "my_service": {
        "$ref": "service:shared",
        "name": "Custom Placeholder Example"
    }
}

Combining Custom Parser and Placeholder

class AtSymbolParser(ReferenceParser):
    """Uses @ for instances: service@instance"""

    def _validate(self, reference: str) -> FormatValidation:
        return FormatValidation(True)

    def _parse(self, reference: str) -> ParsedReference:
        if '@' in reference:
            id_part, instance = reference.split('@', 1)
            return ParsedReference(id=id_part, instance=instance)
        return ParsedReference(id=reference, instance=None)

# Combine custom parser with custom placeholder
mirror = Mirror(
    'myapp',
    parser=AtSymbolParser(),
    placeholder='$build'
)

JSON with both customizations:

{
    "database": {
        "$build": "database@shared_db",
        "host": "localhost",
        "port": 5432
    },
    "service": {
        "$build": "service",
        "database": "$shared_db"
    }
}

Mirror Constructor Options

mirror = Mirror(
    package_name='myapp',           # Package to scan for registers
    parser=DefaultReferenceParser(), # Reference parser (default: DefaultReferenceParser)
    placeholder='$mirror'           # JSON field name (default: '$mirror')
)

Pro Tips

1. Use Meaningful Singleton Names

{
    "$mirror": "database:user_db"     // Good: descriptive
    "$mirror": "cache:cache_1"       // Good: clear purpose
    "$mirror": "service:x"           // Bad: unclear
}

2. Reference Format Best Practices

{
    // Simple instance - no reuse needed
    "logger": {
        "$mirror": "logger",
        "level": "INFO"
    },

    // Singleton - will be reused
    "database": {
        "$mirror": "database:main_db",
        "host": "localhost"
    },

    // Reference the singleton
    "user_service": {
        "$mirror": "user_service",
        "database": "$main_db"  // Inject the singleton
    }
}

3. Understanding Reference Resolution Order

ModelMirror automatically resolves dependencies using topological sorting:

{
    "user_service": {
        "$mirror": "user_service",
        "database": "$main_db",     // Depends on main_db
        "cache": "$redis"           // Depends on redis
    },
    "database": {
        "$mirror": "database:main_db"  // Created first
    },
    "cache": {
        "$mirror": "cache:redis"       // Created second
    }
    // user_service created last (after dependencies)
}

Resolution order: database → cache → user_service

4. Organize Large Configs

# Split large configs into logical sections
class DatabaseConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)
    primary: DatabaseService
    replica: DatabaseService

class ServiceConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)
    user_service: UserService
    auth_service: AuthService

class AppConfig(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)
    databases: DatabaseConfig
    services: ServiceConfig

5. Environment-Specific Configs

# Load different configs per environment
env = os.getenv('ENV', 'dev')
config = mirror.reflect(f'config_{env}.json', AppConfig)

6. Retrieve Instances Flexibly

# Multiple ways to get your instances
user_service = instances.get(UserService)                    # First instance of type
specific_db = instances.get(DatabaseService, '$primary_db') # By singleton name
all_services = instances.get(list[UserService])             # All instances as list
service_map = instances.get(dict[str, UserService])         # All instances as dict

Installation

pip install modelmirror

Requirements

• Python >= 3.10
• Pydantic >= 2.0.0

License

MIT License - see LICENSE file for details.