Schema Limits

💬 In plain words: A junction object is a small "middle table" with two master-details, used when both sides can have many of each other (Students ↔ Courses → Enrollment). It's how you build many-to-many relationships on the platform. 📌 Example: Students and Courses: one student takes many courses, one course has many students. Create Enrollment with two Master-Details — the junction. Ravi's enrollment in 'Apex 101' is one Enrollment record carrying grade and enrollment date. 🧠 The middle table: Many-to-many = two master-details meeting in a small middle object. Students and Courses meet in Enrollment; Skyline's Parcels and Routes meet in a Stop. 🔗 Connects to: The master-detail choice both legs depend on  ·  One busy parent record creates data skew at scale Concept A junction object models many-to-many. It is a custom object with two Master-Detail relationships. The first Mas...

Quick answer: Use a master-detail relationship when the child record means nothing without its parent: it should share the parent's security, be deleted with it, and feed roll-up summary fields. Use a lookup when the child has a life of its own, with its own owner and sharing, and the link to the parent can be optional. Relationships are how Salesforce connects one object to another, like Accounts to Contacts or Orders to Order Items. The type you pick decides who can see the child records, what happens when a parent is deleted, and whether you get totals for free. Getting it wrong is expensive to fix later, so it pays to decide on purpose.