juniorEntity Framework
What are Data Annotations?
Updated Apr 28, 2026
Short answer
Data Annotations are attributes applied to class properties to configure validation and database mapping rules.
Deep explanation
They live in System.ComponentModel.DataAnnotations and define constraints like [Required], [MaxLength(50)], [Table], and [Key]. EF Core reads these during model creation to configure the database schema without needing Fluent API.
Real-world example
Ensuring that a Username column in the database is created with a VARCHAR(50) constraint and NOT NULL.
Common mistakes
- Mixing Data Annotations and Fluent API chaotically
- Fluent API overrides Data Annotations if they conflict.
Follow-up questions
- Can Data Annotations be used for ASP.NET MVC validation?