What are the approaches for working with databases from application code, for example, the Active Record pattern?

There are different approaches and patterns for working with databases from application code, among which Active Record and Data Mapper are two of the most common.

Active Record is a pattern where the model object is directly responsible for storing and loading its data from the database. Each object corresponds to a single record in a table, and methods for CRUD operations (create, read, update, delete) are built into the model class itself.

Example in pseudocode:

class User < ActiveRecord::Base
  # User automatically gets save, update, delete methods
end

user = User.new(name: "Ivan")
user.save  # saves to the database

Data Mapper separates business logic from data access. Model objects are unaware of the database, and a separate layer (repository or mapper) is responsible for converting objects to database records and vice versa.

Additionally, there are ORM (Object-Relational Mapping) libraries that implement these patterns and simplify working with databases, allowing you to write code in a programming language rather than SQL.

The choice of approach depends on the complexity of the project, architectural requirements, and ease of maintenance.