Glossary

Common terms and definitions used in CQL documentation.

A

Active Record

A design pattern where objects carry both data and behavior. In CQL, models that include CQL::ActiveRecord::Model follow this pattern.

Adapter

The database-specific driver that CQL uses to communicate with different database systems. CQL supports PostgreSQL, MySQL, and SQLite adapters.

Association

A relationship between two models. See: belongs_to, has_one, has_many.

B

Belongs To

A relationship where a model references another model via a foreign key. The model with belongs_to holds the foreign key.

C

Callback

A method that is automatically called at specific points during a model's lifecycle (e.g., before_save, after_create).

Column

A single field in a database table, represented as a property in a CQL model.

CRUD

Create, Read, Update, Delete - the four basic operations for persistent storage.

D

Database Context

The connection between a model and its database table, defined using db_context.

Down Migration

The reverse operation of a migration, typically used to rollback changes.

F

Foreign Key

A column that references the primary key of another table, establishing a relationship between tables.

H

Has Many

A relationship where a model has multiple related records in another table.

Has One

A relationship where a model has exactly one related record in another table.

I

Index

A database structure that improves query performance on specific columns.

M

Migration

A versioned change to the database schema, allowing incremental updates to the database structure.

Model

A Crystal struct or class that represents a database table and provides methods for interacting with its data.

O

Optimistic Locking

A concurrency control strategy that detects conflicts when saving records by checking a version column.

ORM

Object-Relational Mapping - a technique for converting data between incompatible type systems (objects and relational databases).

P

Persistence

The process of saving data to a database so it survives beyond the application's runtime.

Primary Key

A unique identifier for each record in a table, typically named id.

Property

A Crystal attribute that maps to a database column.

Q

Query Builder

A fluent interface for constructing SQL queries programmatically.

R

Relationship

A connection between two database tables, represented in CQL using belongs_to, has_one, or has_many.

Rollback

Reverting a database migration to its previous state.

S

Schema

The structure of a database, including its tables, columns, indexes, and relationships.

Scope

A reusable query method defined on a model.

Soft Delete

A technique where records are marked as deleted (using a timestamp) rather than being removed from the database.

T

Table

A collection of related data organized in rows and columns within a database.

Timestamps

Columns that automatically track when records are created (created_at) and updated (updated_at).

Transaction

A sequence of database operations that are executed as a single unit, ensuring all operations succeed or all are rolled back.

U

Up Migration

The forward operation of a migration that applies changes to the database.

UUID

Universally Unique Identifier - a 128-bit identifier that can be used as a primary key.

V

Validation

Rules that ensure data meets certain criteria before being saved to the database.

Version Column

A column used for optimistic locking that increments with each update.