Mini Query Builder

A simple Query Builder web application built with Spring Boot (backend) and H2 in-memory database. It allows users to dynamically select tables, columns, and filters to execute queries and return results as JSON.

This project is a mini version designed for learning and prototyping, with a frontend (can be extended in Svelte) and a REST API backend.

Technologies Used

• Backend: Java, Spring Boot, Spring Web, JPA, H2 Database, Lombok
• Frontend: Optional (Svelte / TailwindCSS)
• Build Tools: Maven
• Database: H2 (in-memory)

Project Structure

src/main/java/com/example/querybuilder/
 ├─ controller/       # REST API endpoints
 ├─ dto/              # DTOs for query and filters
 ├─ model/            # JPA entities (User, Order)
 ├─ repository/       # JPA Repositories
 ├─ service/          # services
 ├─ config/           # DataSeeder for initial data
 └─ utils/            # Optional helpers

Sample Data

The app initializes with two tables:

User Table (app_user)

Order Table (orders)

Endpoints

1️⃣ List Tables

GET /api/tables

Response Example:

["users", "orders"]

2️⃣ List Columns of a Table

GET /api/columns?table={tableName}

Example:

GET /api/columns?table=app_user

Response:

["id","name","email","age"]

3️⃣ Execute Query

POST /api/query

Request Body Example:

{
  "table": "orders",
  "columns": ["product", "amount"],
  "filters": [
    {
      "column": "amount",
      "operator": "<",
      "value": "1000"
    }
  ]
}

Response Example:

[
  ["Phone", 800],
  ["Tablet", 400],
  ["Monitor", 300]
]

Notes:

• table → entity/table name (app_user or orders)

• columns → list of column names to return

• filters → list of filter objects:

  • column → column name
  • operator → =, <, >, like
  • value → string value (numeric columns are parsed automatically)

4. Test endpoints using Postman, curl, or frontend app:

curl http://localhost:8080/api/tables

curl http://localhost:8080/api/columns?table=orders

curl -X POST http://localhost:8080/api/query \
-H "Content-Type: application/json" \
-d '{"table":"orders","columns":["product","amount"],"filters":[{"column":"amount","operator":"<","value":"1000"}]}'

Future Improvements

• Add support for multiple filters with AND/OR logic.
• Add pagination and sorting for results.
• Support JOINs between tables.
• Add a frontend using Svelte for interactive query building.
• Validate table/column names to prevent SQL injection.