请教：如何在.NET Core 2.0项目中配置NHibernate 5.1

Hey there! I’ve worked through setting up NHibernate 5.1 in a .NET Core 2.0 API project before, so I can walk you through the exact steps to get it running smoothly. Here’s a step-by-step guide:

1. Install Required NuGet Packages #

First, you’ll need to add the necessary packages to your project. Open the Package Manager Console or use Visual Studio’s NuGet Package Manager to install these:

• NHibernate (stick to 5.1.x versions to ensure compatibility with .NET Core 2.0)
• Microsoft.Extensions.Configuration.Json (to read configuration from appsettings.json)
• Microsoft.Extensions.DependencyInjection (for integrating NHibernate with .NET Core’s dependency injection)

2. Configure NHibernate #

You have two main options for configuring NHibernate: using a traditional hibernate.cfg.xml file or code-based fluent configuration. Let’s cover both:

Option A: Using hibernate.cfg.xml #

1. Add a new XML file named hibernate.cfg.xml to your project. Set its Copy to Output Directory property to "Copy if newer".
2. Populate it with your database configuration. Here’s an example for SQL Server:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
  <session-factory>
    <!-- Database connection settings -->
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Your_SQL_Server_Connection_String</property>
    <property name="dialect">NHibernate.Dialect.MsSql2012Dialect</property>
    
    <!-- Debug and schema settings -->
    <property name="show_sql">true</property>
    <property name="format_sql">true</property>
    <property name="hbm2ddl.auto">update</property> <!-- Adjust to create/validate/none based on your needs -->
    
    <!-- Map your entities (point to the assembly containing your entity mappings) -->
    <mapping assembly="Your_Project_Assembly_Name" />
  </session-factory>
</hibernate-configuration>

• Replace Your_SQL_Server_Connection_String with your actual database connection string.
• Replace Your_Project_Assembly_Name with the name of your project’s assembly where entity classes and mappings live.

Option B: Fluent Configuration (Code-Based) #

If you prefer code over XML, set up NHibernate programmatically. Here’s a sample:

using NHibernate;
using NHibernate.Cfg;
using NHibernate.Mapping.ByCode;

public static ISessionFactory CreateSessionFactory(string connectionString)
{
    var configuration = new Configuration();
    
    // Database settings
    configuration.DataBaseIntegration(db =>
    {
        db.Driver<NHibernate.Driver.SqlClientDriver>();
        db.Dialect<NHibernate.Dialect.MsSql2012Dialect>();
        db.ConnectionString = connectionString;
        db.LogSqlInConsole = true;
        db.LogFormattedSql = true;
    });
    
    // Add entity mappings (using NHibernate's ByCode approach)
    var mapper = new ModelMapper();
    mapper.AddMappings(typeof(YourEntityMapping).Assembly.GetTypes());
    configuration.AddMapping(mapper.CompileMappingForAllExplicitlyAddedEntities());
    
    return configuration.BuildSessionFactory();
}

• Replace YourEntityMapping with one of your entity mapping classes.

Tip: Pull Connection String from appsettings.json #

To keep your connection string secure and configurable, add it to appsettings.json:

{
  "ConnectionStrings": {
    "DefaultConnection": "Your_SQL_Server_Connection_String"
  }
}

Then retrieve it in your configuration code:

var configBuilder = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json");
var config = configBuilder.Build();
var connectionString = config.GetConnectionString("DefaultConnection");

3. Set Up Dependency Injection in Startup.cs #

Next, register NHibernate’s core components with .NET Core’s DI container. Open Startup.cs and update the ConfigureServices method:

using NHibernate;
using Microsoft.Extensions.Configuration;

public void ConfigureServices(IServiceCollection services)
{
    // Add MVC services
    services.AddMvc();
    
    // Build configuration to access appsettings.json
    var configuration = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appsettings.json")
        .Build();
    
    // Register ISessionFactory as a singleton (one instance for the app's lifetime)
    services.AddSingleton<ISessionFactory>(sp =>
    {
        // Use XML config approach
        var nhConfig = new Configuration();
        nhConfig.Configure(); // Loads hibernate.cfg.xml from output directory
        
        // Uncomment below if using fluent config instead
        // var connectionString = configuration.GetConnectionString("DefaultConnection");
        // return CreateSessionFactory(connectionString);
        
        return nhConfig.BuildSessionFactory();
    });
    
    // Register ISession as scoped (one session per HTTP request)
    services.AddScoped<ISession>(sp =>
    {
        var sessionFactory = sp.GetRequiredService<ISessionFactory>();
        return sessionFactory.OpenSession();
    });
}

4. Use NHibernate in Your Controllers #

Now you can inject ISession into your API controllers to perform database operations. Here’s an example:

using Microsoft.AspNetCore.Mvc;
using NHibernate;
using NHibernate.Linq;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

[Route("api/[controller]")]
public class ProductsController : Controller
{
    private readonly ISession _session;
    
    public ProductsController(ISession session)
    {
        _session = session;
    }
    
    [HttpGet]
    public async Task<IEnumerable<Product>> GetAll()
    {
        return await _session.Query<Product>().ToListAsync();
    }
    
    [HttpGet("{id}")]
    public async Task<IActionResult> GetById(int id)
    {
        var product = await _session.GetAsync<Product>(id);
        if (product == null) return NotFound();
        return Ok(product);
    }
    
    [HttpPost]
    public async Task<IActionResult> Create([FromBody] Product product)
    {
        if (!ModelState.IsValid) return BadRequest(ModelState);
        
        using (var transaction = _session.BeginTransaction())
        {
            await _session.SaveAsync(product);
            await transaction.CommitAsync();
        }
        
        return CreatedAtAction(nameof(GetById), new { id = product.Id }, product);
    }
}

• Ensure your Product entity has valid mappings (either via XML or fluent code).

Common Troubleshooting Tips #

• Mapping Errors: Double-check that all entity mappings are correctly configured and their files are set to "Copy to Output Directory".
• Connection Issues: Verify your connection string is valid and accessible (especially if pulling from appsettings.json).
• DI Scoping: Always register ISessionFactory as a singleton and ISession as scoped—this ensures one session per request, which is NHibernate’s best practice.

内容的提问来源于stack exchange，提问作者seshireddy nangu