shaggy-jars-slide/docs/TAYLORDB_PITFALLS_BEST_PRACTICES.md

TaylorDB Pitfalls & Best Practices

This document captures common mistakes and recommended patterns when using the TaylorDB query builder.

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Common Pitfalls

❌ Pitfall: Not Using exactDay for Dates

// ❌ WRONG
.where("date", "=", "2024-01-15")

// ✅ CORRECT
.where("date", "=", ["exactDay", "2024-01-15"])

❌ Pitfall: Ignoring Nullable Fields

// ❌ WRONG (assumes field is always present)
const user = await queryBuilder
  .selectFrom("users")
  .where("id", "=", 1)
  .executeTakeFirst();
console.log(user.email); // Could be undefined!

// ✅ CORRECT
const user = await queryBuilder
  .selectFrom("users")
  .where("id", "=", 1)
  .executeTakeFirst();
if (user && user.email) {
  console.log(user.email);
}

❌ Pitfall: Using execute() for Single Record

// ❌ WRONG (returns array)
const user = await queryBuilder
  .selectFrom("users")
  .where("id", "=", 1)
  .execute();
console.log(user.name); // Error: user is an array!

// ✅ CORRECT
const user = await queryBuilder
  .selectFrom("users")
  .where("id", "=", 1)
  .executeTakeFirst();
if (user) {
  console.log(user.name);
}

❌ Pitfall: Not Handling Empty Arrays

// ❌ WRONG (fails if users is empty)
const ages = users.map((u) => u.age);
const avg = ages.reduce((a, b) => a + b) / ages.length; // Division by zero!

// ✅ CORRECT
if (users.length === 0) {
  return { average: null };
}
const ages = users
  .map((u) => u.age)
  .filter((a): a is number => a !== undefined);
const avg = ages.reduce((a, b) => a + b, 0) / ages.length;

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Best Practices

1. Always handle undefined and null when working with query results.
2. Use TypeScript types from taylordb/types.ts for type safety.
3. Use executeTakeFirst() when you expect a single record.
4. Filter nullish values before aggregations.
5. Provide defaults for optional fields.
6. Use ["exactDay", date] format for date comparisons.
7. Group related queries in the same function file.
8. Export functions, not raw queries.
9. Document complex queries with JSDoc comments.

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For more topics, see:

• TAYLORDB_BASIC_QUERIES.md for basic reads and filtering
• TAYLORDB_WRITE_OPERATIONS.md for inserts, updates, and deletes
• TAYLORDB_ADVANCED_PATTERNS.md for aggregations, pagination, and conditional queries
• TAYLORDB_FIELD_TYPES.md for field type handling and enums