使用参数化构造函数的通用对象到对象映射

Question

我有一个返回 IDataRecord 的数据访问层。 我有一个为 DataContracts (dto's) 提供服务的 WCF 服务。这些 DataContract 由包含 IDataRecord 的参数化构造函数启动，如下所示：

[DataContract]
public class DataContractItem
{
    [DataMember]
    public int ID;
    [DataMember]
    public string Title;

    public DataContractItem(IDataRecord record)
    {
        this.ID = Convert.ToInt32(record["ID"]);
        this.Title = record["title"].ToString();
    }
}

很遗憾，我无法更改 DAL，因此我不得不使用 IDataRecord 作为输入。但总的来说，这非常有效。映射大部分时间都非常简单，有时它们会更复杂一些，但不是火箭科学。

但是，现在我希望能够使用泛型来实例化不同的 DataContract 以简化 WCF 服务方法。我希望能够做类似的事情：

public T DoSomething<T>(IDataRecord record) {
    ...
return new T(record);
}

所以我尝试了以下解决方案：

1. 使用带有构造函数的泛型类型接口。 不起作用：当然我们不能在接口中定义构造函数

2. 使用静态方法实例化 DataContract 并创建包含此静态方法的类型化接口。 不起作用：当然我们不能在接口中定义静态方法

3. 使用包含 new() 约束的泛型类型接口 不起作用：new() 约束不能包含参数（IDataRecord）

4. 使用工厂对象执行基于 DataContract 类型的映射。 确实有效，但是：不是很干净，因为我现在有一个 switch 语句，所有映射都在一个文件中。

我找不到真正干净的解决方案。有人可以为我解释一下吗？ 该项目对于任何复杂的映射技术来说都太小，对于“基于开关”的工厂实现来说太大了。

Answer 1

我认为您可以为此使用 AutoMapper。这是一个开源项目，它可以让你做你想做的事。在你做某事时，你会这样做：

public TDestination DoSomething<TDestination>(IDataRecord record) {
   return Mapper.Map(reader, reader.GetType(), typeof(TDestination));
}

在此之前，您需要设置地图

Mapper.CreateMap<IDataRecord, MyDestinationType>()

Answer 2

您可以通过反射调用类型构造函数：

public T DoSomething<T>(IDataRecord record)
{
    //do something...

    var ci = typeof(T).GetConstructor(new[] { typeof(IDataRecord) });
    return (T)ci.Invoke(new object[] { record });
}

编辑：上述方法非常脆弱并且依赖于约定，因此另一种方法是为您的数据合约创建一个允许初始化的接口：

public interface IDataContract
{
    void Initialise(IDataRecord record);
}

public T DoSomething<T>(IDataRecord record) where T : IDataContract, new()
{
    //do something

    T contract = new T();
    contract.Initialise(record);

    return contract;
}

Answer 3

这就是我的做法..

DataRow 的扩展方法，可让我将业务对象转换为 DataRow，反之亦然。

/// <summary>
/// Extension methods for DataRow.
/// </summary>
public static class DataRowExtensions
{
    /// <summary>
    /// Converts DataRow into business object.
    /// </summary>
    /// <typeparam name="TEntity">A type that inherits EntityBase.</typeparam>
    /// <param name="dataRow">DataRow object to convert to business object.</param>
    /// <returns>business object created from DataRow.</returns>
    public static TEntity ToEntity<TEntity>(this DataRow dataRow)
        where TEntity : EntityBase, new()
    {
        TEntity entity = new TEntity();
        ExtensionHelper.TransformDataRowToEntity<TEntity, DataRow>(ref dataRow, ref entity);

        return entity;
    }

    /// <summary>
    /// Converts business object into DataRow.
    /// </summary>
    /// <typeparam name="TEntity">A type that inherits EntityBase.</typeparam>
    /// <param name="dataRow">DataRow object to convert business object into.</param>
    /// <param name="entity">Business object which needs to be converted to DataRow.</param>
    public static void FromEntity<TEntity>(this DataRow dataRow, TEntity entity)
        where TEntity : EntityBase, new()
    {
        ExtensionHelper.TransformEntityToDataRow<TEntity, DataRow>(ref entity, ref dataRow);
    }
}

执行转换的实际辅助方法..

/// <summary>
/// Helper methods for transforming data objects into business objects and vice versa.
/// </summary>
/// <remarks>
/// <para>Most important implementation that takes care of universal transformation between business objects and data object.</para>
/// <para>Saves programmers from writing the same old code for every object in the system.</para>
/// </remarks>
public static class ExtensionHelper
{
    /// <summary>
    /// Transforms business object into DataRow.
    /// </summary>
    /// <typeparam name="TEntity">A type that inherits EntityBase.</typeparam>
    /// <typeparam name="TDataRow">A type that inherits DataRow.</typeparam>
    /// <param name="entity">business object which is transformed into DataRow object.</param>
    /// <param name="dataRow">DataRow object which is transformed from business object.</param>
    public static void TransformEntityToDataRow<TEntity, TDataRow>(ref TEntity entity, ref TDataRow dataRow)
        where TDataRow : DataRow
        where TEntity : EntityBase
    {
        IQueryable<DataField> entityFields = entity.GetDataFields();

        foreach (DataColumn dataColoumn in dataRow.Table.Columns)
        {
            if (!dataColoumn.ReadOnly)
            {
                var entityField =
                    entityFields.Single(e => e.DataFieldMapping.MappedField.Equals(dataColoumn.ColumnName, StringComparison.OrdinalIgnoreCase));

                if (entityField.Property.GetValue(entity, null) == null)
                {
                    if (dataColoumn.AllowDBNull)
                    {
                        dataRow[dataColoumn] = System.DBNull.Value;
                    }
                    else
                    {
                        throw new Exception(dataColoumn.ColumnName + " cannot have null value.");
                    }
                }
                else
                {
                    if (entityField.Property.GetType().IsEnum)
                    {
                        dataRow[dataColoumn] = Convert.ToByte(entityField.Property.GetValue(entity, null));
                    }
                    else
                    {
                        dataRow[dataColoumn] = entityField.Property.GetValue(entity, null);
                    }
                }
            }
        }
    }

    /// <summary>
    /// Transforms DataRow into business object.
    /// </summary>
    /// <typeparam name="TEntity">A type that inherits EntityBase.</typeparam>
    /// <typeparam name="TDataRow">A type that inherits DataRow.</typeparam>
    /// <param name="dataRow">DataRow object which is transformed from business object.</param>
    /// <param name="entity">business object which is transformed into DataRow object.</param>
    public static void TransformDataRowToEntity<TEntity, TDataRow>(ref TDataRow dataRow, ref TEntity entity)
        where TDataRow : DataRow
        where TEntity : EntityBase
    {
        IQueryable<DataField> entityFields = entity.GetDataFields();

        foreach (var entityField in entityFields)
        {
            if (dataRow[entityField.DataFieldMapping.MappedField] is System.DBNull)
            {
                entityField.Property.SetValue(entity, null, null);
            }
            else
            {
                if (entityField.Property.GetType().IsEnum)
                {
                    Type enumType = entityField.Property.GetType();
                    EnumConverter enumConverter = new EnumConverter(enumType);
                    object enumValue = enumConverter.ConvertFrom(dataRow[entityField.DataFieldMapping.MappedField]);
                    entityField.Property.SetValue(entity, enumValue, null);
                }
                else
                {
                    entityField.Property.SetValue(entity, dataRow[entityField.DataFieldMapping.MappedField], null);
                }
            }
        }
    }
}

这是我的示例业务对象的外观。请注意自定义属性..

/// <summary>
/// Represents User.
/// </summary>
[TableMapping("Users", "User", "Users")]
public class User : EntityBase
{
    #region Constructor(s)
    /// <summary>
    /// Initializes a new instance of the User class.
    /// </summary>
    public User()
    {
    }
    #endregion

    #region Properties

    #region Default Properties - Direct Field Mapping using DataFieldMappingAttribute

    /// <summary>
    /// Gets or sets the ID value of the AppUser object.
    /// </summary>
    [DataFieldMapping("UserID")]
    [DataObjectFieldAttribute(true, true, false)]
    [NotNullOrEmpty(Message = "UserID From UserDetails Table Is Required.")]
    public override int Id
    {
        get;
        set;
    }

    /// <summary>
    /// Gets or sets the Username value of the User object.
    /// </summary>
    [DataFieldMapping("UserName")]
    [Searchable]
    [NotNullOrEmpty(Message = "Username Is Required.")]
    public string UserName
    {
        get;
        set;
    }

    /// <summary>
    /// Gets or sets the FirstName value of the AppUser object.
    /// </summary>
    [DataFieldMapping("FirstName")]
    [Searchable]
    public string FirstName
    {
        get;
        set;
    }

    /// <summary>
    /// Gets or sets the LastName value of the AppUser object.
    /// </summary>
    [DataFieldMapping("LastName")]
    [Searchable]
    public string LastName
    {
        get;
        set;
    }

    /// <summary>
    /// Gets or sets the WebSite value of the AppUser object.
    /// </summary>
    [DataFieldMapping("WebSite")]
    [ValidURL(Message = "Website is not in Proper Format.")]
    public string WebSite
    {
        get;
        set;
    }

    /// <summary>
    /// Gets or sets the ContactNumber value of the AppUser object.
    /// </summary>
    [DataFieldMapping("ContactNumber")]
    [Searchable]
    public string ContactNumber
    {
        get;
        set;
    }

    /// <summary>
    /// Gets or sets a value indicating whether AppUser Object is active or inactive.
    /// </summary>
    [DataFieldMapping("IsActive")]
    public bool IsActive
    {
        get;
        set;
    }

    /// <summary>
    /// Gets or sets the BirthDate value of the AppUser object.
    /// </summary>
    [DataFieldMapping("BirthDate")]
    public DateTime? BirthDate
    {
        get;
        set;
    }

    #region Derived Properties

    /// <summary>
    /// Gets the full name of the AppUser
    /// </summary>
    public string FullName
    {
        get { return this.FirstName + " " + this.LastName; }
    }

    /// <summary>
    /// Gets the Age value of the AppUser
    /// </summary>
    public int Age
    {
        get { return this.BirthDate.HasValue ? this.BirthDate.Value.AgeInYears() : 0; }
    }

    #endregion

    #endregion

}

这是我的客户端代码..

    /// <summary>
    /// Gets User object by user name.
    /// </summary>
    /// <param name="username">UserName of the user</param>
    /// <returns>User Object</returns>
    public static User GetUserByUsername(string username)
    {
        try
        {
            return Adapter.GetUserByUserName(username)[0].ToEntity<User>();
        }
        catch
        {
            return null;
        }
    }