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Column

Represents a database column with various constraints and properties.

Parameters:

  • column_name (str) –

    The name of the column.

  • data_type (str) –

    The data-type of the column (e.g., integer,varchar,date).

  • primary_key (Optional[bool], default: False ) –

    Whether the column is a primary key or not . Defaults to False.

  • foreign_key (Optional[bool], default: False ) –

    Whether the column is a foreign key or not. Defaults to False.

  • unique (Optional[bool], default: False ) –

    Whether the column has a unique constraint. Defaults to False.

  • null (Optional[bool], default: True ) –

    Whether the column allows NULL values. Defaults to True.

  • max_length (Optional[int], default: None ) –

    The maximum length of the column (for data types like varchar,char).

  • precision (Optional[int], default: None ) –

    The precision for numeric types (total number of digits). Defaults to None.

  • scale (Optional[int], default: None ) –

    The scale for numeric types (number of digits to the right of the decimal).

  • referenced_column (Optional[str], default: None ) –

    The name of the referenced column if current column is a foreign key.

  • referenced_table (Optional[str], default: None ) –

    The name of the referenced table if current column is a foreign key.

  • on_delete (Optional[str], default: None ) –

    The ON DELETE strategy for foreign key constraints.Defaults to CASCADE.

  • foreign_key_constraint_name (Optional[str], default: None ) –

    The name of the foreign key constraint. Defaults to None.

Usage

from polly.auth import Polly from polly.atlas import Atlas, Table, Column

Polly.auth("")

column = Column(column_name="user_id", data_type="integer", primary_key=True, unique=True, null=False)

Constraints

  • Primary Key: Combines not null + unique , ensuring each row has a unique identifier.
  • Foreign Key: Establishes foriegn key relationships between tables.
  • Unique: Ensures all values in a column are distinct.
  • Null: Ensures if a column can be nullable or not.

Supported Data Types

Numeric Data Types

  • smallint (2 bytes): Range -32,768 to 32,767
  • integer (4 bytes): Range -2,147,483,648 to 2,147,483,647
  • bigint (8 bytes): Range -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
  • decimal(p,s) / numeric(p,s): Variable storage, exact precision up to 38 digits
  • real (4 bytes): Single-precision floating-point numbers
  • double precision (8 bytes): Double-precision floating-point numbers
  • serial / bigserial: Auto-incrementing integer types
  • money (8 bytes): Fixed-point for currency values

Note: bigserial can only be used as a primary key column.

    `precision` and `scale` settings are applicable only to decimal and numeric types.

Character Data Types

  • char(max_length) / character(max_length): Fixed-length string (padded with spaces)
  • varchar(max_length) / character varying(max_length): Variable-length string
  • text: Unlimited-length string

Note: max_length is required for char and varchar. text does not require a length constraint.

Date & Time Data Types

  • date: Stores calendar dates (YYYY-MM-DD)
  • time: Stores time of day (HH:MM:SS)
  • timestamp/ timestamp without time zone: Stores date and time without timezone(2025-04-03 14:30:00)
  • timestamptz/timestamp with time zone: Stores date and time with timezone(2025-04-03 14:30:00+05:30)
  • interval: Represents a duration (e.g., "2 hours 30 minutes")

Boolean & JSON Data Types

  • boolean: Stores true, false values
  • json: Stores structured JSON data

Examples

Using Primary Key

This is how you declare a column as Primary Key

column = Column(column_name="id", data_type="integer", primary_key=True, unique=True, null=False)

Using Foreign Key

A foreign key enforces referential integrity by linking a column to another table.

column = Column(column_name="patient_id",data_type="integer",foreign_key=True,referenced_table="patients",referenced_column="id"on_delete="CASCADE")

Unique Constraint

Ensures that column contains unique values.

column = Column(column_name="prescription", data_type="varchar", max_length=255, unique=True, null=False)

Numeric Precision & Scale

For defining numeric columns with specific precision and scale.

column = Column(column_name="weight", data_type="decimal", precision=10, scale=2, null=False)

column = Column(column_name="amount", data_type="numeric", precision=12, scale=4, null=False)

JSON Column for File Metadata

Stores structured JSON data, particularly useful for file storage references.

column = Column(column_name="metadata", data_type="json")