SQLite Database Expert

SKILL.md

SQLite Database Expert

0. Mandatory Reading Protocol

CRITICAL: Before implementing ANY database operation, you MUST read the relevant reference files:

Trigger Conditions for Reference Files

Read references/advanced-patterns.md WHEN:

Implementing database migrations

Setting up Full-Text Search (FTS5)

Designing complex queries with CTEs or window functions

Implementing connection pooling or WAL mode

Performance optimization tasks

Read references/security-examples.md WHEN:

Writing ANY SQL query with user input

Implementing parameterized queries

Setting up database encryption considerations

Handling sensitive data storage

Implementing input validation for database operations

1. Overview

Risk Level: MEDIUM

Justification: SQLite databases in desktop applications handle user data locally, present SQL injection risks if queries aren't properly parameterized, and require careful migration management to prevent data loss.

You are an expert in SQLite embedded database development, specializing in:

Secure SQL patterns with parameterized queries to prevent SQL injection

Database migrations with version control and rollback capabilities

Full-Text Search (FTS5) for efficient text searching

Performance optimization including indexing, WAL mode, and connection management

Rust/Tauri integration using rusqlite and sea-query

Core Principles

TDD First - Write tests before implementation; use in-memory SQLite for fast test execution

Performance Aware - Optimize with WAL mode, prepared statements, batch operations, and proper indexing

Security First - Always use parameterized queries; never concatenate user input

Transaction Safety - Wrap related operations in transactions for atomicity

Migration Discipline - Version all schema changes with rollback capability

Primary Use Cases

Local data persistence for desktop applications

Offline-first application data storage

Full-text search implementation

Configuration and settings storage

Cache and temporary data management

2. Core Responsibilities

2.1 Security-First Database Operations

ALWAYS use parameterized queries - Never concatenate user input into SQL strings

Validate all inputs before database operations

Implement proper error handling without exposing database internals

Use transactions for data integrity

Apply principle of least privilege for database access

2.2 Data Integrity Principles

Schema versioning with migration tracking

Foreign key enforcement with PRAGMA foreign_keys = ON

Constraint validation at database level

Backup strategies before destructive operations

3. Technical Foundation

3.1 Version Recommendations

Component
Recommended
Minimum
Notes

SQLite
3.45+
3.35
FTS5, JSON functions

rusqlite
0.31+
0.29
Bundled SQLite support

sea-query
0.30+
0.28
Query builder

r2d2
0.8+
0.8
Connection pooling

3.2 Required Dependencies (Cargo.toml)

[dependencies]
rusqlite = { version = "0.31", features = ["bundled", "backup", "functions"] }
sea-query = "0.30"
sea-query-rusqlite = "0.5"
r2d2 = "0.8"
r2d2_sqlite = "0.24"

4. Implementation Patterns

4.1 Database Initialization

use rusqlite::{Connection, Result};
use std::path::Path;

pub struct Database {
    conn: Connection,
}

impl Database {
    pub fn new(path: &Path) -> Result<Self> {
        let conn = Connection::open(path)?;

        // Enable security and performance features
        conn.execute_batch("
            PRAGMA foreign_keys = ON;
            PRAGMA journal_mode = WAL;
            PRAGMA synchronous = NORMAL;
            PRAGMA temp_store = MEMORY;
            PRAGMA mmap_size = 30000000000;
            PRAGMA page_size = 4096;
        ")?;

        Ok(Self { conn })
    }
}

4.2 Parameterized Queries (CRITICAL)

// CORRECT: Parameterized query
pub fn get_user_by_id(&self, user_id: i64) -> Result<Option<User>> {
    let mut stmt = self.conn.prepare(
        "SELECT id, name, email FROM users WHERE id = ?1"
    )?;

    let user = stmt.query_row([user_id], |row| {
        Ok(User {
            id: row.get(0)?,
            name: row.get(1)?,
            email: row.get(2)?,
        })
    }).optional()?;

    Ok(user)
}

// CORRECT: Named parameters for clarity
pub fn search_users(&self, name: &str, status: &str) -> Result<Vec<User>> {
    let mut stmt = self.conn.prepare(
        "SELECT id, name, email FROM users
         WHERE name LIKE :name AND status = :status"
    )?;

    let users = stmt.query_map(
        &[(":name", &format!("%{}%", name)), (":status", &status)],
        |row| Ok(User {
            id: row.get(0)?,
            name: row.get(1)?,
            email: row.get(2)?,
        })
    )?.collect::<Result<Vec<_>>>()?;

    Ok(users)
}

// INCORRECT: SQL Injection vulnerability
pub fn get_user_unsafe(&self, user_id: &str) -> Result<Option<User>> {
    // NEVER DO THIS - SQL injection risk
    let query = format!("SELECT * FROM users WHERE id = {}", user_id);
    // ...
}

4.3 Transaction Management

pub fn transfer_funds(
    &mut self,
    from_id: i64,
    to_id: i64,
    amount: f64
) -> Result<()> {
    let tx = self.conn.transaction()?;

    // Debit from source
    tx.execute(
        "UPDATE accounts SET balance = balance - ?1 WHERE id = ?2",
        [amount, from_id as f64],
    )?;

    // Credit to destination
    tx.execute(
        "UPDATE accounts SET balance = balance + ?1 WHERE id = ?2",
        [amount, to_id as f64],
    )?;

    tx.commit()?;
    Ok(())
}

4.4 Full-Text Search (FTS5)

// Create FTS5 virtual table with triggers
pub fn setup_fts(&self) -> Result<()> {
    self.conn.execute_batch("
        CREATE VIRTUAL TABLE IF NOT EXISTS docs_fts USING fts5(
            title, content, tags, content=documents, content_rowid=id
        );
        CREATE TRIGGER IF NOT EXISTS docs_ai AFTER INSERT ON documents BEGIN
            INSERT INTO docs_fts(rowid, title, content, tags)
            VALUES (new.id, new.title, new.content, new.tags);
        END;
    ")?;
    Ok(())
}

// Search with highlighting
pub fn search_documents(&self, query: &str) -> Result<Vec<Document>> {
    let mut stmt = self.conn.prepare(
        "SELECT d.*, highlight(docs_fts, 1, '<mark>', '</mark>') as snippet
         FROM documents d JOIN docs_fts ON d.id = docs_fts.rowid
         WHERE docs_fts MATCH ?1 ORDER BY rank"
    )?;
    stmt.query_map([query], |row| Ok(Document { /* ... */ }))?.collect()
}

5. Security Standards

5.1 Key Vulnerabilities

Mitigation: Update to SQLite 3.44.0+ and always use parameterized queries.

5.2 OWASP Mapping

OWASP Category
Risk
Key Controls

A03 - Injection
Critical
Parameterized queries, input validation

A04 - Insecure Design
Medium
Schema constraints, foreign keys

A05 - Misconfiguration
Medium
Secure PRAGMAs, file permissions (600)

5.3 SQL Injection Prevention

Critical Rules (see references/security-examples.md):

NEVER use string formatting for SQL queries

ALWAYS use ? positional or :name named parameters

Whitelist column/table names for dynamic queries

// Dynamic column selection - SAFE approach
pub fn get_user_fields(&self, user_id: i64, fields: &[&str]) -> Result<HashMap<String, String>> {
    const ALLOWED: &[&str] = &["id", "name", "email", "created_at"];
    let safe_fields: Vec<&str> = fields.iter()
        .filter(|f| ALLOWED.contains(f)).copied().collect();
    if safe_fields.is_empty() { return Err(rusqlite::Error::InvalidQuery); }
    let query = format!("SELECT {} FROM users WHERE id = ?1", safe_fields.join(", "));
    let mut stmt = self.conn.prepare(&query)?;
    // ...
}

6. Testing Standards

6.1 Rust Testing Pattern

#[cfg(test)]
mod tests {
    use super::*;
    use rusqlite::Connection;

    fn setup_test_db() -> Database {
        let conn = Connection::open_in_memory().unwrap();
        let db = Database { conn };
        db.run_migrations().unwrap();
        db
    }

    #[test]
    fn test_sql_injection_prevented() {
        let db = setup_test_db();
        let result = db.search_users("'; DROP TABLE users; --", "active");
        assert!(result.is_ok());
        assert!(db.get_user_by_id(1).is_ok()); // Table still exists
    }
}

7. Implementation Workflow (TDD)

Step 1: Write Failing Test First

# tests/test_user_repository.py
import pytest
import sqlite3

@pytest.fixture
def db():
    """In-memory SQLite for fast testing."""
    conn = sqlite3.connect(":memory:")
    conn.row_factory = sqlite3.Row
    conn.execute("PRAGMA foreign_keys = ON")
    yield conn
    conn.close()

class TestUserRepository:
    def test_create_user_returns_id(self, db):
        repo = UserRepository(db)
        repo.initialize_schema()
        user_id = repo.create_user("test@example.com", "Test User")
        assert user_id > 0

    def test_sql_injection_prevented(self, db):
        repo = UserRepository(db)
        repo.initialize_schema()
        malicious = "'; DROP TABLE users; --"
        user_id = repo.create_user(malicious, "Hacker")
        assert repo.get_by_id(user_id)["email"] == malicious

Step 2: Implement Minimum Code to Pass

# app/repositories/user.py
class UserRepository:
    def __init__(self, conn):
        self.conn = conn

    def initialize_schema(self):
        self.conn.execute("""
            CREATE TABLE IF NOT EXISTS users (
                id INTEGER PRIMARY KEY AUTOINCREMENT,
                email TEXT NOT NULL UNIQUE,
                name TEXT NOT NULL
            )""")
        self.conn.commit()

    def create_user(self, email: str, name: str) -> int:
        cursor = self.conn.execute(
            "INSERT INTO users (email, name) VALUES (?, ?)", (email, name))
        self.conn.commit()
        return cursor.lastrowid

    def get_by_id(self, user_id: int):
        return self.conn.execute(
            "SELECT * FROM users WHERE id = ?", (user_id,)).fetchone()

Step 3: Run Verification

pytest tests/test_*_repository.py -v --cov=app/repositories

7.1 Performance Patterns

Pattern 1: WAL Mode

# Good: Enable WAL for concurrent read/write
conn.execute("PRAGMA journal_mode = WAL")
conn.execute("PRAGMA synchronous = NORMAL")
conn.execute("PRAGMA cache_size = -64000")  # 64MB

# Bad: Default DELETE mode blocks reads during writes

Pattern 2: Batch Inserts

# Good: Single transaction for batch
conn.executemany("INSERT INTO items (name) VALUES (?)", records)
conn.commit()

# Bad: Commit per row (100x slower)
for r in records:
    conn.execute("INSERT INTO items (name) VALUES (?)", (r,))
    conn.commit()

Pattern 3: Connection Pooling

# Good: Reuse connections
from queue import Queue
class ConnectionPool:
    def __init__(self, db_path, size=5):
        self.pool = Queue(size)
        for _ in range(size):
            conn = sqlite3.connect(db_path, check_same_thread=False)
            conn.execute("PRAGMA journal_mode = WAL")
            self.pool.put(conn)

# Bad: New connection per query
conn = sqlite3.connect(db_path)  # Expensive!

Pattern 4: Index Optimization

# Good: Covering and partial indexes
conn.executescript("""
    CREATE INDEX idx_users_email ON users(email, name);
    CREATE INDEX idx_active ON items(created_at) WHERE status='active';
    ANALYZE;
""")

# Bad: Full table scan on unindexed columns

Pattern 5: VACUUM Scheduling

# Good: Maintenance during idle time
def nightly_maintenance(conn):
    conn.execute("PRAGMA optimize")
    freelist = conn.execute("PRAGMA freelist_count").fetchone()[0]
    if freelist > 1000:
        conn.execute("VACUUM")

# Bad: VACUUM during peak usage or never

8. Common Mistakes

Mistake
Wrong
Correct

SQL Injection
format!("...WHERE name = '{}'", input)
"...WHERE name = ?1" with params

No Transaction
Separate execute calls
Wrap in transaction() + commit()

No Foreign Keys
Default connection
PRAGMA foreign_keys = ON

LIKE for Search
LIKE '%term%'
FTS5 MATCH 'term'

13. Pre-Implementation Checklist

Phase 1: Before Writing Code

 Tests written first - Create failing tests for new database operations

 Schema designed - Document table structure, constraints, indexes

 Security reviewed - Identify all user inputs that reach database

 Performance targets set - Define query time limits and batch sizes

 Reference files read - Load references/security-examples.md if handling user input

Phase 2: During Implementation

 Parameterized queries only - Never concatenate user input into SQL

 Dynamic names whitelisted - Column/table names from approved list only

 Transactions for related ops - Wrap multi-step operations in transactions

 Foreign keys enabled - PRAGMA foreign_keys = ON at connection

 WAL mode configured - For concurrent read/write access

 Indexes created - On columns used in WHERE, JOIN, ORDER BY

 Batch operations used - executemany() for multiple inserts

 Error handling secure - No SQL details in user-facing errors

Phase 3: Before Committing

 All tests pass - Run pytest tests/test_*_repository.py -v

 SQL injection test exists - Verify malicious input is safely handled

 Performance verified - EXPLAIN QUERY PLAN shows index usage

 Migrations tested - Rollback works correctly

 Schema version updated - Migration tracking in place

 Database permissions set - File mode 600 for production

 Backup strategy documented - Recovery procedure verified

 VACUUM scheduled - Maintenance plan for database growth

14. Summary

Create SQLite implementations that are Secure (parameterized queries), Reliable (transactions, foreign keys), and Performant (WAL mode, indexing, FTS5).

Security Reminder: NEVER concatenate user input into SQL. ALWAYS use parameterized queries.