Data Annotations in Entity Framework Code First

This post will help yo uunderstand how to create Data Annotations in database tables using Entity Framework Code First.

Introduction

Entity Framework provides two ways to add configuration to model classes.

• DataAnnotation Attribute - Data Annotation Attributes can only add the some property of the table.
  
  Namespace ( System.ComponentModel.DataAnnotations)
  
  
• DataAnnotation Schema Attribute - Data Annotation Schemas are used to change or modify the structure of table.
  
  Namespace (System.ComponentModel.DataAnnotations.Schema)

Data Annotation Attributes

• Key: Key is mainly used to define the primary or composite key on table.
  
  
• ConcurrencyCheck: ConcurrencyCheck annotation allows you to flag one or more properties to be used for concurrency checking in the database when a user edits or deletes an entity.
  
  
• StringLength: StringLength is user to define the length of string allowed in table
  
  
• MinLength: MinLength define the minimum required length of string.
  
  
• MaxLength: MaxLength define the minimum required length of string.
  
  
• Required: The Required annotation will ensure that property has data in it.

Data Annotation Schema Attributes:

• Table: Provides the alternate table name.
  
• Column: Used to provide the column name or column schema.
  
• Foreign Key: Create a relationship 
  
• Index: To defined the clustered/non clustered index.
  
• Complex Type: Make the class ascComplex type.

Example:

Here is the example code of how these attributes can be used.

Employee Class:

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
namespace EntityFrameworkCodeFirst
{
    [Table("tblEmp")]
    public class Employee
    {
        //Defined Primary Key
        [Key]
        public int ID
        {
            get;
            set;
        }
        [Required]
        public string Title
        {
            get;
            set;
        }
        [StringLength(25)]
        public string EmployeeName
        {
            get;
            set;
        }
        [MinLength(5)]
        public decimal Salary
        {
            get;
            set;
        }
        //Foreign key for Department
        [ForeignKey("DepartmentID")]
        public int DepartmentID
        {
            get;
            set;
        }
    }
}

Department Class

public class Department
{
    public int DepartmentID
    {
        get;
        set;
    }
    public string DepartmentName
    {
        get;
        set;
    }
    public List < Employee > Employees
    {
        get;
        set;
    }
}