How to discover table properties from SQLAlchemy mapped object

How to discover table properties from SQLAlchemy mapped object

In SQLAlchemy, you can discover table properties from a mapped object using the __table__ attribute of the mapped class. This attribute provides access to the underlying Table object associated with the mapped class, and you can inspect various properties of the table, such as column names, data types, constraints, and more. Here's how you can do it:

Assuming you have an SQLAlchemy model like this:

from sqlalchemy import create_engine, Column, Integer, String from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() class User(Base): __tablename__ = 'users' id = Column(Integer, primary_key=True) username = Column(String(255)) email = Column(String(255))

You can discover table properties as follows:

from sqlalchemy import inspect # Create an SQLAlchemy engine and bind it to the Base engine = create_engine('sqlite:///my_database.db') Base.metadata.create_all(engine) # Get an Inspector to inspect the database inspector = inspect(engine) # Get the User table object from the mapped class user_table = User.__table__ # Use the Inspector to discover table properties columns = inspector.get_columns(user_table) # Print column information for column in columns: print(f"Column: {column['name']}, Type: {column['type']}, Primary Key: {column['primary_key']}, Nullable: {column['nullable']}")

In this example:

  1. We create an SQLAlchemy engine and bind it to the Base class using create_engine and Base.metadata.create_all.

  2. We use inspect(engine) to create an Inspector object for the database engine.

  3. We access the User table object using User.__table__.

  4. We use the Inspector to get column information for the User table using inspector.get_columns(user_table).

  5. Finally, we iterate through the columns and print their names, data types, whether they are primary keys, and whether they are nullable.

This approach allows you to dynamically discover table properties from SQLAlchemy mapped objects and can be useful for various purposes such as database introspection, data validation, and schema management.

Examples

  1. "SQLAlchemy mapped object table properties"

    • Description: This query is aimed at finding methods or techniques to discover the properties of a table from a SQLAlchemy mapped object.
    from sqlalchemy import inspect def discover_table_properties(mapped_object): mapper = inspect(mapped_object) table_name = mapper.tables[0].name columns = mapper.columns.keys() return table_name, columns # Example usage: from your_module import YourMappedObject table_name, columns = discover_table_properties(YourMappedObject) print("Table Name:", table_name) print("Columns:", columns)

    This code snippet utilizes SQLAlchemy's inspect function to extract information about the mapped object, including the table name and column names.

  2. "SQLAlchemy mapped object table columns"

    • Description: This query seeks ways to retrieve the column properties of a table from a SQLAlchemy mapped object.
    from sqlalchemy import inspect def get_table_columns(mapped_object): mapper = inspect(mapped_object) columns = mapper.columns.keys() return columns # Example usage: from your_module import YourMappedObject columns = get_table_columns(YourMappedObject) print("Columns:", columns)

    This code snippet uses SQLAlchemy's inspect function to obtain the column names of the table associated with the mapped object.

  3. "Discover SQLAlchemy mapped object table schema"

    • Description: This query aims to find methods or functions to discover the schema or structure of a table from a SQLAlchemy mapped object.
    from sqlalchemy import inspect def discover_table_schema(mapped_object): mapper = inspect(mapped_object) table = mapper.tables[0] schema = table.schema return schema # Example usage: from your_module import YourMappedObject schema = discover_table_schema(YourMappedObject) print("Table Schema:", schema)

    This code snippet utilizes SQLAlchemy's inspect function to extract the schema information of the table associated with the mapped object.

  4. "Retrieve table properties from SQLAlchemy mapped class"

    • Description: This query is focused on finding ways to retrieve properties, such as column names, from a SQLAlchemy mapped class.
    from sqlalchemy import inspect def get_table_properties(mapped_object): mapper = inspect(mapped_object) table_name = mapper.tables[0].name columns = [column.name for column in mapper.columns] return table_name, columns # Example usage: from your_module import YourMappedObject table_name, columns = get_table_properties(YourMappedObject) print("Table Name:", table_name) print("Columns:", columns)

    This code snippet utilizes SQLAlchemy's inspect function to retrieve the table name and column names associated with the mapped object.

  5. "SQLAlchemy mapped object table metadata"

    • Description: This query aims to find information or methods to access the metadata of a table from a SQLAlchemy mapped object.
    from sqlalchemy import inspect def get_table_metadata(mapped_object): mapper = inspect(mapped_object) metadata = mapper.tables[0].metadata return metadata # Example usage: from your_module import YourMappedObject metadata = get_table_metadata(YourMappedObject) print("Table Metadata:", metadata)

    This code snippet utilizes SQLAlchemy's inspect function to access the metadata of the table associated with the mapped object.

  6. "SQLAlchemy mapped object table constraints"

    • Description: This query seeks methods or techniques to discover the constraints applied to a table from a SQLAlchemy mapped object.
    from sqlalchemy import inspect def discover_table_constraints(mapped_object): mapper = inspect(mapped_object) table_constraints = mapper.tables[0].constraints return table_constraints # Example usage: from your_module import YourMappedObject constraints = discover_table_constraints(YourMappedObject) print("Table Constraints:", constraints)

    This code snippet utilizes SQLAlchemy's inspect function to retrieve the constraints applied to the table associated with the mapped object.

  7. "Access table properties from SQLAlchemy mapped object"

    • Description: This query aims to find methods or functions to access various properties of a table from a SQLAlchemy mapped object.
    from sqlalchemy import inspect def access_table_properties(mapped_object): mapper = inspect(mapped_object) table_name = mapper.tables[0].name columns = [column.name for column in mapper.columns] constraints = mapper.tables[0].constraints return table_name, columns, constraints # Example usage: from your_module import YourMappedObject table_name, columns, constraints = access_table_properties(YourMappedObject) print("Table Name:", table_name) print("Columns:", columns) print("Constraints:", constraints)

    This code snippet utilizes SQLAlchemy's inspect function to access various properties of the table associated with the mapped object, including table name, columns, and constraints.

  8. "Retrieve table details from SQLAlchemy mapped object"

    • Description: This query is focused on finding ways to retrieve detailed information about a table from a SQLAlchemy mapped object.
    from sqlalchemy import inspect def retrieve_table_details(mapped_object): mapper = inspect(mapped_object) table_details = { 'name': mapper.tables[0].name, 'columns': [column.name for column in mapper.columns], 'constraints': mapper.tables[0].constraints } return table_details # Example usage: from your_module import YourMappedObject details = retrieve_table_details(YourMappedObject) print("Table Details:", details)

    This code snippet utilizes SQLAlchemy's inspect function to retrieve detailed information about the table associated with the mapped object, including table name, columns, and constraints.

  9. "SQLAlchemy mapped object table primary key"

    • Description: This query aims to find methods or techniques to discover the primary key of a table from a SQLAlchemy mapped object.
    from sqlalchemy import inspect def get_primary_key(mapped_object): mapper = inspect(mapped_object) primary_key = mapper.primary_key return primary_key # Example usage: from your_module import YourMappedObject primary_key = get_primary_key(YourMappedObject) print("Primary Key:", primary_key)

    This code snippet utilizes SQLAlchemy's inspect function to retrieve the primary key of the table associated with the mapped object.

  10. "SQLAlchemy mapped object table foreign keys"

    • Description: This query seeks methods or techniques to discover the foreign keys of a table from a SQLAlchemy mapped object.
    from sqlalchemy import inspect def get_foreign_keys(mapped_object): mapper = inspect(mapped_object) foreign_keys = mapper.foreign_keys return foreign_keys # Example usage: from your_module import YourMappedObject foreign_keys = get_foreign_keys(YourMappedObject) print("Foreign Keys:", foreign_keys)

    This code snippet utilizes SQLAlchemy's inspect function to retrieve the foreign keys of the table associated with the mapped object.

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