Enforcing Data Restrictions in SQLite: Beyond Built-in Types

1. Create a separate table: This table will hold the actual allowed values for your ENUM. It will have two columns:

   • One column to store the actual value (e.g., text).
   • Another column (optional) to store an order or code (e.g., integer).

This way, you can control what values are allowed in your main table while still leveraging SQLite's built-in data types like INTEGER or TEXT. This approach is sometimes referred to as a "poor man's ENUM".

Here are some additional points to consider:

• You can enforce data integrity using checks or triggers to ensure values in your main table always reference a valid entry in the separate table.
• This approach adds some complexity compared to a native ENUM data type, but it offers a way to achieve similar functionality within SQLite.

-- Create the table to store allowed values (like an ENUM)
CREATE TABLE Status (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  status_text TEXT UNIQUE NOT NULL
);

-- Insert some sample allowed values
INSERT INTO Status (status_text) VALUES ('Active'), ('Pending'), ('Cancelled');

-- Create the main table referencing the allowed values
CREATE TABLE Orders (
  order_id INTEGER PRIMARY KEY AUTOINCREMENT,
  customer_name TEXT NOT NULL,
  status_id INTEGER NOT NULL REFERENCES Status(id),
  -- Other table columns...
  FOREIGN KEY (status_id) REFERENCES Status(id)
);

-- This enforces that status_id in Orders must reference a valid id in Status

In this example:

1. We create a table named "Status" with two columns:
   • id: An auto-incrementing integer for a unique identifier.
   • status_text: Text to store the actual status value (e.g., "Active", "Pending", "Cancelled"). The UNIQUE constraint ensures no duplicate entries.
2. We insert some sample values into the "Status" table.
3. We create the main table named "Orders".
   • It has a column named "status_id" which is an integer referencing the "id" column in the "Status" table.
   • The FOREIGN KEY constraint enforces that any value in "status_id" must exist as a valid ID in the "Status" table. This effectively limits the allowed values in "status_id" to the predefined options in "Status".

This method uses a check constraint on the desired column in your main table. The constraint defines a condition that limits the values to the allowed options.

Here's an example:

CREATE TABLE Orders (
  order_id INTEGER PRIMARY KEY AUTOINCREMENT,
  customer_name TEXT NOT NULL,
  status TEXT CHECK(status IN ('Active', 'Pending', 'Cancelled')),
  -- Other table columns...
);

In this approach:

• The status column is defined as TEXT.
• A check constraint is added that verifies the status value must be one of the listed options: "Active", "Pending", or "Cancelled".

This method is simpler than the separate table approach, but it can become cumbersome if you have a large number of allowed values.

Custom data types (user-defined functions):

While SQLite doesn't support native ENUM types, you can create custom data types using user-defined functions (UDFs). This approach involves creating functions to handle data manipulation and validation for your "ENUM-like" type.

This method offers more flexibility but requires more development effort compared to the other methods. It's generally recommended for complex scenarios where built-in data types aren't sufficient.

Choosing the right method:

The best method depends on your specific needs. Here's a quick guide:

• Separate table approach: Good for clarity and maintainability, especially with many allowed values.
• Check constraint: Simpler to implement but less scalable for a large number of options.
• Custom data types: Offers more control but requires more development effort.