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Domain-Specific Languages: Design and Implementation

Case Study 2: Extending Data Query Language

Explore how to extend the Data Query Language to interact with a mock database, fetching and processing data based on query conditions. Learn to modify code generation and classes to create a more powerful DSL suited for real-world data retrieval tasks.

We'll cover the following...

In this lesson, we will extend the Data Query Language (DQL) functionality developed in the previous lesson by integrating it with a database to fetch data. This extension is essential to enhance DQL’s capabilities, allowing it to interact with structured data sources. Each step in this process plays a crucial role in ensuring that the language remains expressive, efficient, and adaptable to evolving requirements. By following these steps, we will refine DQL to retrieve and process data from a database while maintaining its usability and performance. By the end of this lesson, you will have a deeper understanding of how to modify and expand a language, making it more powerful and suited to real-world scenarios.

Extending DQL

To extend DQL, let’s simulate a database table and fetch data based on a DQL query. We will add a mock database with sample data and modify the code generation step to fetch data that matches the query conditions.

Define a mock database

We’ll create a simple Database class to represent data in memory, containing a list of rows. Each row will be described as a Map<String, Object> to store column names and values.

import java.util.*;
public class Database {
    // Sample data representing the database
    private List<Map<String, String>> employees = new ArrayList<>();
    public Database() {
        // Initialize with some data
        Map<String, String> employee1 = new HashMap<>();
        employee1.put("name", "Alice");
        employee1.put("age", "35");
        Map<String, String> employee2 = new HashMap<>();
        employee2.put("name", "Bob");
        employee2.put("age", "28");
        Map<String, String> employee3 = new HashMap<>();
        employee3.put("name", "Charlie");
        employee3.put("age", "40");
        employees.add(employee1);
        employees.add(employee2);
        employees.add(employee3);
    }
    // Method to get table data based on table name
    public List<Map<String, String>> getTableData(String tableName) {
        // Return employee data for "employees" table
        if (tableName.equals("employees")) {
            return employees;
        }
        return new ArrayList<>();
    }
}
Database.java

Modify Query class to fetch data

Modify the generateCode method of ...