Repository pattern in PHP - Step-by-Step Execution

Concept Flow - Repository pattern

Client calls Repository

↓

Repository handles data logic

↓

Repository calls Data Source (DB, API)

↓

Data Source returns data

↓

Repository returns data to Client

The client asks the repository for data. The repository talks to the data source, gets data, and returns it to the client.

Execution Sample

PHP

<?php
interface UserRepository {
  public function findUserById(int $id): array;
}

class UserRepo implements UserRepository {
  public function findUserById(int $id): array {
    // Simulate DB call
    return ['id' => $id, 'name' => 'Alice'];
  }
}

$userRepo = new UserRepo();
$user = $userRepo->findUserById(1);
print_r($user);
?>

This code shows a repository interface and class that returns user data by ID, simulating a database call.

Execution Table

Step	Action	Method Called	Input	Output
1	Create UserRepo instance	-	-	UserRepo object created
2	Call findUserById	findUserById	1	Array ['id' => 1, 'name' => 'Alice']
3	Print result	-	-	Array printed: id=1, name=Alice
4	End	-	-	No more actions

💡 All steps completed, user data retrieved and printed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
$userRepo	null	UserRepo object	UserRepo object	UserRepo object	UserRepo object
$user	null	null	['id' => 1, 'name' => 'Alice']	['id' => 1, 'name' => 'Alice']	['id' => 1, 'name' => 'Alice']

Key Moments - 2 Insights

Why do we use an interface for the repository?

The interface defines what methods the repository must have, so the client code can use any class that follows this interface without changing. See step 2 in execution_table where findUserById is called on the repository.

Does the client know how data is fetched?

No, the client only calls the repository method. The repository hides the data source details. This is shown in step 2 where the repository returns data without exposing database logic.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output of findUserById when called with 1?

A Null

B Error message

C Array with id=1 and name='Alice'

D Empty array

💡 Hint

Check step 2 in execution_table where findUserById returns the array.

At which step is the UserRepo object created?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at step 1 in execution_table where the UserRepo instance is created.

If the repository method returned data from an API instead of a database, what changes in the execution_table?

A The method called would change

B The output would still be the same format

C The client code would change

D The UserRepo object would not be created

💡 Hint

Repository hides data source, so output format stays same as shown in variable_tracker.

Concept Snapshot

Repository pattern:
- Defines an interface for data access
- Repository class implements data fetching logic
- Client calls repository, not data source directly
- Hides data source details (DB, API)
- Makes code easier to change and test

Full Transcript

The Repository pattern helps separate data access logic from the rest of the code. The client calls methods on a repository interface. The repository class implements these methods and fetches data from a database or other source. This hides the details of data fetching from the client. In the example, a UserRepo class implements a method to find a user by ID and returns user data as an array. The client creates the repository object, calls the method, and gets the data. This makes the code cleaner and easier to maintain.