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...

Extending DQL
Playground

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

1.Before We Begin

2.Introduction

3.Language Design

4.Language Implementation

5.ANTLR v4

6.JastAdd

7.A Language Implementation with ANTLR v4 and JastAdd

8.Conclusion

9.Appendix

Case Study 2: Extending Data Query Language

Extending DQL

Define a mock database

Modify Query class to fetch data