Question

我有一个数据库，用于保存存储在另一个系统中的Id项，并在代码中反序列化为一个对象。我正在尝试使用Fluent NHibernate构建一个域模型实体，该实体由来自数据库和外部服务的数据组成。一个例子将更好地解释这一点。在数据库中，我有一个如下表：

CREATE TABLE entities
(
  id integer NOT NULL,
  custom_thing text NOT NULL,
  CONSTRAINT entities_id_pk PRIMARY KEY (id)
);

它是PostgreSQL但问题不是数据库特定的。现在在代码中我有这些类：

class Entity
{
    public virtual int Id { get; set; }

    public virtual CustomThing CustomThing { get; set; }
}

class CustomThing
{
    public string Id { get; set; }
    public string Name { get; set; }
}

我正在尝试使用CustomMap来定义映射：

class EntityMap : ClassMap<Entity>
{
    public EntityMap()
    {
        Table("entities");
        Id(e => e.Id, "id").GeneratedBy.Assigned();
        // Map(e => e.CustomThing, "custom_thing");
    }
}

问题是：如何映射CustomThing？这是一个试图映射Entity类的程序（如果针对PostgreSQL数据库运行，需要FluentNHibernate包和NpgSQL）。为简单起见，我只需在代码中创建CustomThing的实例：

class Program
{
    // How to use this in mapping?
    static CustomThing[] _customThings =
    {
        new CustomThing {Id = "abc", Name = "ABC"},
        new CustomThing {Id = "def", Name = "DEF"}
    };

    static void Main()
    {
        using (ISessionFactory sessionFactory = Fluently.Configure()
            .Database(PostgreSQLConfiguration.Standard
                .ConnectionString(
                    @"Server=localhost; Database=test_nhibernate; User Id=postgres; Password=little_secret;"))
            .Mappings(m => m.FluentMappings.AddFromAssemblyOf<Entity>())
            .BuildSessionFactory())
        {
            using (ISession session = sessionFactory.OpenSession())
            {
                var entity = session.Get<Entity>(1);

                Console.WriteLine($"{entity?.Id} {entity?.CustomThing?.Name}");
            }
        }
        Console.ReadLine();
    }
}

输出当然只是Id属性值，因为未定义CustomThing的映射。是否可以配置映射，以便我可以将参数传递给它，并通过Id属性以某种方式将custom_thing列值映射到_customThings中的对象？

Answer 1

是的，您可以通过保存Id来获取，并在代码中获取其余数据，或者将映射器中的所有内容都返回给您，如果您选择第二个选项，则可以请遵循以下代码：

[Serializable]
public class CustomThingUserType : IUserType {
    public new bool Equals(object x, object y) {
        if (object.ReferenceEquals(x, y))
            return true;

        if (x == null || y == null)
            return false;

        return x.Equals(y);
    }

    public int GetHashCode(object x) {
        if (x == null)
            return 0;

        return x.GetHashCode();
    }

    public object NullSafeGet(IDataReader rs, string[] names, object owner) {
        if (names.Length == 0)
            throw new ArgumentException("Expecting at least one column");

        int id = (int)NHibernateUtil.Int32.NullSafeGet(rs, names[0]);

        var obj = new CustomThing { Id = id };

        // here you can grab your data from external service

        return obj;
    }

    public void NullSafeSet(IDbCommand cmd, object value, int index) {
        var parameter = (DbParameter)cmd.Parameters[index];

        if (value == null) {
            parameter.Value = 0;
        }
        else {
            parameter.Value = ((CustomThing)value).Id;
        }
    }

    public object DeepCopy(object value) {
        return value;
    }

    public object Replace(object original, object target, object owner) {
        return original;
    }

    public object Assemble(object cached, object owner) {
        return cached;
    }

    public object Disassemble(object value) {
        return value;
    }

    public SqlType[] SqlTypes {
        get {
            return new SqlType[] { new SqlType(DbType.Int32) };
        }
    }

    public Type ReturnedType {
        get { return typeof(CustomThing); }
    }

    public bool IsMutable {
        get { return false; }
    }
}

在Fluent NHibernate中映射自定义类型属性

1 个答案: