How to perform data validation in TypeORM?

TypeORM validation can be implemented in the following ways:

1. Use class-validator library: Install: npm install class-validator

   Use validation decorators in entities:

   typescript
   import { IsEmail, IsNotEmpty, Length } from 'class-validator';
   
   @Entity()
   export class User {
     @PrimaryGeneratedColumn()
     id: number;
     
     @Column()
     @IsNotEmpty()
     @Length(2, 50)
     name: string;
     
     @Column()
     @IsEmail()
     email: string;
   }

2. Validate before saving:

   typescript
   import { validate } from 'class-validator';
   
   const user = new User();
   user.name = 'John';
   user.email = 'invalid-email';
   
   const errors = await validate(user);
   if (errors.length > 0) {
     console.log('Validation failed:', errors);
   }

3. Use subscriber for automatic validation: Create a subscriber to automatically validate during BeforeInsert and BeforeUpdate.

4. Database-level validation: Use database constraints with @Column options like nullable, unique, length, etc.

It's recommended to combine class-validator with database constraints to ensure data integrity and security.