如何使用 NHibernate (Fluent) 将 DateTime 属性映射到数据库中的 2 个 varchar 列？

Question

我正在处理一个遗留数据库，该数据库在某些表中具有日期和时间字段作为 char(8) 列（格式分别为 yyyyMMdd 和 HH:mm:ss）。如何将 2 个字符列映射到单个 .NET DateTime 属性？我尝试了以下方法，但我当然会收到“无法访问 setter”错误，因为 DateTime Date 和 TimeOfDay 属性是只读的：

public class SweetPocoMannaFromHeaven
{    
    public virtual DateTime? FileCreationDateTime { get; set; }
}

.

mapping.Component<DateTime?>(x => x.FileCreationDateTime,
            dt =>
            {
                dt.Map(x => x.Value.Date,
                    "file_creation_date");
                dt.Map(x => x.Value.TimeOfDay,
                    "file_creation_time");
            });

我也尝试为 DateTime 定义一个 IUserType，但我无法弄清楚。我已经做了很多谷歌搜索来寻找答案，但我仍然无法弄清楚。处理这个 stupid 遗留数据库约定的最佳选择是什么？一个代码示例会很有帮助，因为关于其中一些更晦涩的场景的文档并不多。

Answer 1

您需要一个 ICompositeUserType 来处理多个列。您需要加强错误检查、解析格式等，但这里是您的起点。

HTH，
浆果

public class LegacyDateUserType : ICompositeUserType
{

    public new bool Equals(object x, object y)
    {
        if (x == null || y == null) return false;
        return ReferenceEquals(x, y) || x.Equals(y);
    }

    public int GetHashCode(object x) {
        return x == null ? typeof (DateTime).GetHashCode() + 473 : x.GetHashCode();
    }

    public object NullSafeGet(IDataReader dr, string[] names, ISessionImplementor session, object owner)
    {
        if (dr == null) return null;

        var datePortion = NHibernateUtil.String.NullSafeGet(dr, names[0], session, owner) as string;
        var timePortion = NHibernateUtil.String.NullSafeGet(dr, names[1], session, owner) as string;

        var date = DateTime.Parse(datePortion);
        var time = DateTime.Parse(timePortion);
        return date.AddTicks(time.Ticks);
    }

    ///<summary>
    /// Write an instance of the mapped class to a prepared statement. Implementors 
    /// should handle possibility of null values. A multi-column type should be written 
    /// to parameters starting from index.
    ///</summary>
    public void NullSafeSet(IDbCommand cmd, object value, int index, ISessionImplementor session) {
        if (value == null) {
            // whatever
        }
        else {
            var date = (DateTime) value;
            var datePortion = date.ToString("your date format");
            NHibernateUtil.String.NullSafeSet(cmd, datePortion, index, session);
            var timePortion = date.ToString("your time format");
            NHibernateUtil.String.NullSafeSet(cmd, timePortion, index + 1, session);
        }
    }

    public object GetPropertyValue(object component, int property)
    {
        var date = (DateTime)component;
        return property == 0 ? date.ToString("your date format") : date.ToString("your time format");
    }

    public void SetPropertyValue(object component, int property, object value)
    {
        throw new NotSupportedException("DateTime is an immutable object.");
    }

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

    public object Disassemble(object value, ISessionImplementor session) { return value; }

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

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

    ///<summary>Get the "property names" that may be used in a query.</summary>
    public string[] PropertyNames { get { return new[] { "DATE_PORTION", "TIME_PORTION" }; } }

    ///<summary>Get the corresponding "property types"</summary>
    public IType[] PropertyTypes { get { return new IType[] { NHibernateUtil.String, NHibernateUtil.String }; } }

    ///<summary>The class returned by NullSafeGet().</summary>
    public Type ReturnedClass { get { return typeof(DateTime); } }

    ///<summary>Are objects of this type mutable?</summary>
    public bool IsMutable { get { return false; } }

}

=== 流畅映射（假设自动映射 w/覆盖类）====

 public void Override(AutoMapping<MyClass> m)
 {
     ....
     m.Map(x => x.MyDateTime).CustomType<LegacyDateUserType>();
 }