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What is a composite key?

Q: What is a composite key?

Short answer: How to define composite keys in EF Core? A composite key is a primary key made of multiple columns. EF Core does not support composite keys via data annotations, so you must use Fluent API: modelBuilder.Entity () .HasKey(od => new { od.OrderId, od.ProductId }); Real-world example (ShopNest) ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction. Say this in the interview Define — one clear sentence (the short answer above). Example — relate it to a project like ShopNest or your real work. Trade-off — when you would not use it.

Short answer: How to define composite keys in EF Core? A composite key is a primary key made of multiple columns. EF Core does not support composite keys via data annotations, so you must use Fluent API: modelBuilder.Entity<OrderDetail>() .HasKey(od => new { od.OrderId, od.ProductId });

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

Define — one clear sentence (the short answer above).
Example — relate it to a project like ShopNest or your real work.
Trade-off — when you would not use it.

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