Dba

MongoDB DBA Skill

Prerequisites

This skill requires mongosh (MongoDB Shell) to be installed and available on PATH.

Connection Details

Connection settings are stored in the .NET API configuration:

1. Check appsettings.json at src/expenses-api/Expenses.Api/src/appsettings.json for the MongoSettings section:
   • MongoSettings:ConnectionString — the MongoDB connection URI
   • MongoSettings:Database — the database name
2. User secrets may override these values. Check with:

   cd src/expenses-api/Expenses.Api/src && dotnet user-secrets list
   

3. If neither source has credentials, ask the user for the connection string.

Connecting

mongosh "<ConnectionString>" --eval '<query>'
# Or for interactive exploration:
mongosh "<ConnectionString>"

Always target the correct database:

mongosh "<ConnectionString>" --eval 'use("<Database>"); <query>'

Database Schema

Refer to references/SCHEMA.md for detailed collection schemas. Summary:

All field names are camelCase in MongoDB (via CamelCaseElementNameConvention). The _id fields are stored as ObjectId.

Common Queries

List recent expenses

db.Expenses.find().sort({ timestamp: -1 }).limit(10)

Expenses for a specific month

db.Expenses.find({
  timestamp: {
    $gte: ISODate("2026-01-01"),
    $lt: ISODate("2026-02-01")
  }
}).sort({ timestamp: -1 })

Aggregate total by category

db.Expenses.aggregate([
  { $group: { _id: "$category", total: { $sum: "$amount" } } },
  { $sort: { total: -1 } }
])

Monthly spending totals

db.Expenses.aggregate([
  { $group: {
    _id: { year: { $year: "$timestamp" }, month: { $month: "$timestamp" } },
    total: { $sum: "$amount" },
    count: { $sum: 1 }
  }},
  { $sort: { "_id.year": -1, "_id.month": -1 } }
])

Search expenses by tag

db.Expenses.find({ tags: "groceries" })

List all categories

db.Categories.find()

List all tags

db.Tags.find()

Count expenses per category

db.Expenses.aggregate([
  { $group: { _id: "$category", count: { $sum: 1 } } },
  { $sort: { count: -1 } }
])

Find top expenses by amount

db.Expenses.find().sort({ amount: -1 }).limit(10)

Safety Rules

1. Read-only by default — Only execute read operations (find, aggregate, count, distinct) unless the user explicitly requests a mutation.
2. Mutations require confirmation — Before running any insert, update, delete, drop, or replaceOne operation, show the user the exact command and ask for explicit confirmation.
3. Never drop collections or databases without the user typing the exact confirmation.
4. Always limit result sets — Use .limit() on queries that could return large datasets to avoid overwhelming output.
5. Show the query before executing — Let the user review the mongosh command before running it.