Tolitech.ConstraintValidator

A static library for managing and validating database constraint exceptions in a database-agnostic way, with specific implementations for PostgreSQL and SQL Server.

Overview

This library helps you identify and handle integrity constraint exceptions (primary key, foreign key, not null, check) thrown by databases, converting them into custom exceptions for easier handling in your application.

• Tolitech.ConstraintValidator: Core and interface for validators.
• Tolitech.ConstraintValidator.PostgreSql: PostgreSQL-specific validator.
• Tolitech.ConstraintValidator.SqlServer: SQL Server-specific validator.

Installation

Add the desired package to your project:

dotnet add package Tolitech.ConstraintValidator

# For PostgreSQL:
dotnet add package Tolitech.ConstraintValidator.PostgreSql

# For SQL Server:
dotnet add package Tolitech.ConstraintValidator.SqlServer

Basic Usage

1. Register the validator

At application startup (e.g., Startup):

using Tolitech.ConstraintValidator;
using Tolitech.ConstraintValidator.PostgreSql;
using Tolitech.ConstraintValidator.SqlServer;

// For PostgreSQL
ConstraintValidatorManager.AddValidator(new PostgreSqlConstraintValidator());

// For SQL Server
ConstraintValidatorManager.AddValidator(new SqlServerConstraintValidator());

2. Handle database exceptions

When catching exceptions from database operations:

try
{
    // Database operation
}
catch (Exception ex)
{
    Exception handled = ConstraintValidatorManager.Handle(ex);
    if (handled is DatabaseConstraintViolationException)
    {
        // Custom logic for constraint violations
    }
    else
    {
        // Other handling
    }
}

Examples of Handled Exceptions

PostgreSQL

• Primary key violation: SqlState = "23505"
• Foreign key violation: SqlState = "23503"
• Check constraint violation: SqlState = "23514"
• Not null violation: SqlState = "23502"

SQL Server

• Primary key violation: Number = 2627
• Foreign key violation: Number = 547
• Not null violation: Number = 515

Advanced Integration

Remove or clear validators

ConstraintValidatorManager.RemoveValidator(yourValidator);
ConstraintValidatorManager.ClearValidators();

Custom implementation

Implement IConstraintValidator to create validators for other databases:

public class MyDbConstraintValidator : IConstraintValidator
{
    public Exception HandleConstraintViolation(Exception exception)
    {
        // Your logic
    }
}

Benefits

• Centralized constraint exception handling.
• Easy for internationalization and logging.
• Extensible for multiple databases.

Modern Examples

Usage with Entity Framework Core

try
{
    await dbContext.SaveChangesAsync();
}
catch (Exception ex)
{
    var handled = ConstraintValidatorManager.Handle(ex);
    if (handled is PrimaryKeyViolationException)
        // Notify user about duplicate
}

Usage in APIs

[HttpPost]
public IActionResult Create([FromBody] MyObject obj)
{
    try
    {
        // ...
    }
    catch (Exception ex)
    {
        var handled = ConstraintValidatorManager.Handle(ex);
        if (handled is DatabaseConstraintViolationException)
            return BadRequest(handled.Message);
        throw;
    }
}

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Tolitech.ConstraintValidator makes constraint exception handling simple, clean, and ready for multiple databases.