{"appId":"mongodb-app","version":370,"selectedAngularVersion":20,"item":{"id":"mongodb-lesson-024","conceptKey":"subject-find-documents","subjectId":"subject-find-documents","title":"Find Documents","summary":"Learn Find Documents from beginner fundamentals through production decisions expected from an experienced MongoDB engineer.","baseContent":"<h2>Find Documents</h2><p><strong>MongoMart experience path:</strong> This topic is taught through the same MongoMart e-commerce system used throughout the course.</p><h3>Shared database</h3><pre><code>// Core MongoMart collections\ncustomers: { _id, name, email, addresses[], createdAt }\nproducts:  { _id, sku, name, categoryId, price, attributes, stock }\ncarts:     { _id, customerId, items[], expiresAt }\norders:    { _id, orderNo, customerId, items[], status, total, orderedAt }\ninventory: { _id, sku, available, reserved, warehouseId }\npayments:  { _id, orderId, providerRef, status, amount }\nnotifications: { _id, customerId, type, payload, sentAt }</code></pre><h3>Beginner foundation</h3><p>Define Find Documents, identify what problem it solves, and run the smallest working example before adding abstraction.</p><h3>Real-world scenario</h3><p>A customer searches products and views recent orders while staff update inventory without overwriting another field.</p><h3>Practical example</h3><pre><code>db.orders.find(\n  { customerId: ObjectId(\"64b000000000000000000001\"), status: { $in: [\"paid\", \"shipped\"] } },\n  { orderNo: 1, total: 1, orderedAt: 1 }\n).sort({ orderedAt: -1 }).limit(20)</code></pre><h3>Intermediate reasoning</h3><ul><li>Predict the exact documents read or changed.</li><li>Test missing fields, nulls, duplicates, empty arrays, and boundary values.</li><li>Validate the result with a second query or assertion.</li></ul><h3>Advanced production use</h3><p>Measure behavior with realistic cardinality and concurrency. Add indexes or distributed features only after identifying the actual access pattern and failure mode.</p><h3>10-year experience perspective</h3><p>Review query shape, atomicity boundary, idempotency, pagination stability, write conflicts, error contracts, and retry safety.</p><h3>Review checklist</h3><ul><li>Correctness and atomicity</li><li>Schema evolution and backward compatibility</li><li>Performance and capacity evidence</li><li>Security and privacy</li><li>Failure recovery, monitoring, and ownership</li></ul><section data-nonversioned-curriculum=\"1\"><h3>Easy example</h3><p>Find one customer by email and return only the fields needed by the screen.</p><pre><code>db.customers.findOne(\n  { email: \"asha@example.com\" },\n  { name: 1, email: 1, status: 1 }\n)</code></pre><h3>How to verify the easy example</h3><ul><li>Run it with representative input.</li><li>Confirm the expected output.</li><li>Try one missing, invalid, or boundary value.</li></ul><h3>Advanced example</h3><p>Aggregate completed orders by customer, rank revenue, and verify the access pattern with execution statistics.</p><pre><code>db.orders.aggregate([\n  { $match: { status: \"completed\" } },\n  { $group: { _id: \"$customerId\", revenue: { $sum: \"$total\" } } },\n  { $setWindowFields: {\n      sortBy: { revenue: -1 },\n      output: { revenueRank: { $denseRank: {} } }\n  } },\n  { $limit: 20 }\n]).explain(\"executionStats\")</code></pre><h3>Advanced review</h3><ul><li>Explain the tradeoffs and assumptions.</li><li>Test failure, scale, security, and recovery behavior.</li><li>Capture evidence from tests, execution plans, logs, or review output.</li></ul><h3>Additional practical guidance</h3><div><h3>Find Documents production detail</h3><p>Review query shape, atomicity boundary, idempotency, pagination stability, write conflicts, error contracts, and retry safety.</p><h3>Required evidence</h3><ul><li>A repeatable setup and test case</li><li>The expected successful result</li><li>One failure or edge case</li><li>Relevant explain, profiler, log, or monitoring output</li><li>A rollback or recovery approach</li></ul></div></section>","detailId":"mongodb-lesson-024-detail","versions":[],"isActive":true,"detailIsActive":true,"lessonVersions":[],"selectedVersion":20,"content":"","updatedAt":"2026-08-01T09:43:04.474Z","details":[{"id":"mongodb-lesson-024","conceptKey":"subject-find-documents","subjectId":"subject-find-documents","title":"Find Documents","summary":"Learn Find Documents from beginner fundamentals through production decisions expected from an experienced MongoDB engineer.","baseContent":"<h2>Find Documents</h2><p><strong>MongoMart experience path:</strong> This topic is taught through the same MongoMart e-commerce system used throughout the course.</p><h3>Shared database</h3><pre><code>// Core MongoMart collections\ncustomers: { _id, name, email, addresses[], createdAt }\nproducts:  { _id, sku, name, categoryId, price, attributes, stock }\ncarts:     { _id, customerId, items[], expiresAt }\norders:    { _id, orderNo, customerId, items[], status, total, orderedAt }\ninventory: { _id, sku, available, reserved, warehouseId }\npayments:  { _id, orderId, providerRef, status, amount }\nnotifications: { _id, customerId, type, payload, sentAt }</code></pre><h3>Beginner foundation</h3><p>Define Find Documents, identify what problem it solves, and run the smallest working example before adding abstraction.</p><h3>Real-world scenario</h3><p>A customer searches products and views recent orders while staff update inventory without overwriting another field.</p><h3>Practical example</h3><pre><code>db.orders.find(\n  { customerId: ObjectId(\"64b000000000000000000001\"), status: { $in: [\"paid\", \"shipped\"] } },\n  { orderNo: 1, total: 1, orderedAt: 1 }\n).sort({ orderedAt: -1 }).limit(20)</code></pre><h3>Intermediate reasoning</h3><ul><li>Predict the exact documents read or changed.</li><li>Test missing fields, nulls, duplicates, empty arrays, and boundary values.</li><li>Validate the result with a second query or assertion.</li></ul><h3>Advanced production use</h3><p>Measure behavior with realistic cardinality and concurrency. Add indexes or distributed features only after identifying the actual access pattern and failure mode.</p><h3>10-year experience perspective</h3><p>Review query shape, atomicity boundary, idempotency, pagination stability, write conflicts, error contracts, and retry safety.</p><h3>Review checklist</h3><ul><li>Correctness and atomicity</li><li>Schema evolution and backward compatibility</li><li>Performance and capacity evidence</li><li>Security and privacy</li><li>Failure recovery, monitoring, and ownership</li></ul><section data-nonversioned-curriculum=\"1\"><h3>Easy example</h3><p>Find one customer by email and return only the fields needed by the screen.</p><pre><code>db.customers.findOne(\n  { email: \"asha@example.com\" },\n  { name: 1, email: 1, status: 1 }\n)</code></pre><h3>How to verify the easy example</h3><ul><li>Run it with representative input.</li><li>Confirm the expected output.</li><li>Try one missing, invalid, or boundary value.</li></ul><h3>Advanced example</h3><p>Aggregate completed orders by customer, rank revenue, and verify the access pattern with execution statistics.</p><pre><code>db.orders.aggregate([\n  { $match: { status: \"completed\" } },\n  { $group: { _id: \"$customerId\", revenue: { $sum: \"$total\" } } },\n  { $setWindowFields: {\n      sortBy: { revenue: -1 },\n      output: { revenueRank: { $denseRank: {} } }\n  } },\n  { $limit: 20 }\n]).explain(\"executionStats\")</code></pre><h3>Advanced review</h3><ul><li>Explain the tradeoffs and assumptions.</li><li>Test failure, scale, security, and recovery behavior.</li><li>Capture evidence from tests, execution plans, logs, or review output.</li></ul><h3>Additional practical guidance</h3><div><h3>Find Documents production detail</h3><p>Review query shape, atomicity boundary, idempotency, pagination stability, write conflicts, error contracts, and retry safety.</p><h3>Required evidence</h3><ul><li>A repeatable setup and test case</li><li>The expected successful result</li><li>One failure or edge case</li><li>Relevant explain, profiler, log, or monitoring output</li><li>A rollback or recovery approach</li></ul></div></section>","detailId":"mongodb-lesson-024-detail","versions":[],"isActive":true,"detailIsActive":true,"lessonVersions":[],"selectedVersion":20,"content":"","updatedAt":"2026-08-01T09:43:04.474Z"}]}}