Validation
Learn how to use validation attributes to automatically generate backend and frontend validation rules.
Overview
Spiderly simplifies validation across your application by allowing you to annotate your entity classes with attributes.
Validation attributes fall into two categories:
- Spiderly custom validation attributes
- EF Core attributes from
System.ComponentModel.DataAnnotations
Validation attributes are used to:
- Automatically generate backend (DTO-level) validation.
- Automatically generate frontend form validation rules.
- Leave database validation to EF Core.
Behavior Based on Attribute Type:
- EF Core attributes will result in database schema changes. When you use them, remember to run database migration and update.
- Spiderly backend validation attributes require rebuilding the backend to take effect.
CustomValidatorAttribute
Usage
Defines custom validation rules for the decorated property or class (can be used on DTOs as well as entities). Supports chaining of multiple rules using dot notation, e.g., EmailAddress().Length(5, 50).
Examples:
// Class-level validation
[CustomValidator("RuleFor(x => x.Email).EmailAddress().Length(5, 50);")]
[CustomValidator("RuleFor(x => x.Name).Length(2, 100);")]
public class User : BusinessObject<long>
{
public string Email { get; set; }
public string Name { get; set; }
}
// Property-level validation
public class User : BusinessObject<long>
{
[CustomValidator("EmailAddress()")]
[CustomValidator("Length(5, 50)")]
public string Email { get; set; }
}GreaterThanOrEqualToAttribute
Usage
Validates that a numeric property value is greater than or equal to a specified number. This attribute provides both server-side and client-side validation.
Example:
public class Product : BusinessObject<long>
{
[GreaterThanOrEqualTo(0)] // StockQuantity must be 0 or higher
public int StockQuantity { get; set; }
}PrecisionAttribute
Usage
Specifies the precision and scale for a decimal property. Useful for controlling how many digits are stored in total (precision) and how many of them are after the decimal point (scale).
Applies to the server-side, client-side validation and affects the EF Core model and will generate corresponding SQL column definition.
Example:
public class Product : BusinessObject<long>
{
[Precision(18, 2)] // Allows up to 18 digits total, with 2 after the decimal point
public decimal Price { get; set; }
}RangeAttribute
Usage
Validates that a numeric value falls within a specified inclusive range.
Applies to the server-side, client-side validation and affects the EF Core model and will generate corresponding SQL column definition.
Example:
public class Product : BusinessObject<long>
{
[Range(1, 1000)] // Price must be between 1 and 1000 (inclusive)
public decimal Price { get; set; }
}RequiredAttribute
Usage
Specifies that a value must be provided for the decorated property, enforcing non-null values.
Applies to the server-side, client-side validation and affects the EF Core model and will generate corresponding SQL column definition.
Example:
public class User : BusinessObject<long>
{
[Required] // Name cannot be null or empty
public string Name { get; set; }
}StringLengthAttribute
Usage
Specifies the minimum and/or maximum length for a string property.
Applies to the server-side, client-side validation and affects the EF Core model and will generate corresponding SQL column definition.
Best Practice
Always apply StringLength to string properties. If omitted, EF Core will map them to NVARCHAR(MAX) by default, which can negatively impact performance.
Example:
public class User : BusinessObject<long>
{
[StringLength(50, MinimumLength = 2)] // Name must be between 2 and 50 characters
public string Name { get; set; }
}