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类的泛型工厂?

factory generics c#

Amanda Kitson · 技术社区 · 16 年前

我正在尝试创建一个类,该类使用工厂查找正确的类,然后调用该类上的方法。我做错了,因为visualstudio中的intellisense不断提醒我错误,当我尝试访问应该在类中的方法时,工厂返回它们不可用。

有人能告诉我我做错了什么吗?

下面是我试图获取类引用的代码:

DBBase dal = DALFactory.GetDAL(typeof(T));

            myCollection = dal.GetByCriteria(myCriteria, sortExpression, startRowIndex, maximumRows, propertyNamesToBypassInstantiation);

以下是DALFactory类的代码:

    internal static class DALFactory
    {
        // GetParser
        internal static DBBase GetDAL(System.Type BOType)
        {
            switch (BOType.Name)
            {
                case "Person":
                    return new PersonDB();
}
            // if we reach this point then we failed to find a matching type. Throw 
            // an exception.
            throw new Exception("Unknown Type");
        }
}

public abstract class DBBase
{
    protected static T GetSingleBO<T>(ref SqlCommand command) where T : BOBase
    {
        return GetSingleBO<T>(ref command, null);
    }


    protected static T GetSingleBO<T>(ref SqlCommand command, List<string> propertyNamesToBypassInstantiation) where T : BOBase
    {
        T BO = default(T);
        try
        {
            command.Connection.Open();
            SqlDataReader reader = command.ExecuteReader();
            if (reader.HasRows)
            {
                reader.Read();
                BOParser parser = BOParserFactory.GetParser(typeof(T));
                parser.PopulateOrdinals(reader);
                if (propertyNamesToBypassInstantiation == null)
                {
                    BO = (T)parser.PopulateBO(reader);
                }
                else
                {
                    BO = (T)parser.PopulateBO(reader, propertyNamesToBypassInstantiation);
                }
                reader.Close();
            }
            else
            {
                // Whever there's no data, we return null.
                BO = default(T);
            }
        }
        catch (Exception ex)
        {
            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("Error populating data: {0}", ex.Message);
            if (ex.InnerException != null)
            {
                sb.AppendFormat("  --  Inner Exception: {0}", ex.InnerException.Message);
            }
            throw new Exception(sb.ToString(), ex);
        }
        finally
        {
            command.Connection.Close();
            command.Connection.Dispose();
        }

        // return the BO, it's either populated with data or null.
        return BO;
    }


    protected static EquatableList<T> GetBOEquatableList<T>(ref SqlCommand command) where T : BOBase
    {
        return GetBOEquatableList<T>(ref command, null);
    }

   protected static EquatableList<T> GetBOEquatableList<T>(ref SqlCommand command, List<string> propertyNamesToBypassInstantiation) where T : BOBase
    {
        EquatableList<T> BOList = new EquatableList<T>();
        try
        {
            command.Connection.Open();
            SqlDataReader reader = command.ExecuteReader();
            if (reader.HasRows)
            {
                // Get a parser for this BO type and populate
                // the ordinals.
                BOParser parser = BOParserFactory.GetParser(typeof(T));
                parser.PopulateOrdinals(reader);

                // Use the parser to build our list of BOs.
                while (reader.Read())
                {
                    T BO = default(T);
                    if (propertyNamesToBypassInstantiation == null)
                    {
                        BO = (T)parser.PopulateBO(reader);
                    }
                    else
                    {
                        BO = (T)parser.PopulateBO(reader, propertyNamesToBypassInstantiation);
                    }
                    BOList.Add(BO);
                }
                reader.Close();
            }
        }
        catch (Exception ex)
        {
            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("Error populating data: {0}", ex.Message);
            if (ex.InnerException != null)
            {
                sb.AppendFormat("  --  Inner Exception: {0}", ex.InnerException.Message);
            }
            throw new Exception(sb.ToString(), ex);
        }
        finally
        {
            command.Connection.Close();
            command.Connection.Dispose();
        }

        return BOList;
    }

    protected static int GetBOCount(ref SqlCommand command)
    {
        int count = 0;

        try
        {
            command.CommandType = CommandType.StoredProcedure;
            DbParameter idParam = command.CreateParameter();
            idParam.DbType = DbType.Int32;
            idParam.Direction = ParameterDirection.InputOutput;
            idParam.ParameterName = "@recordCount";
            idParam.Value = 0;
            command.Parameters.Add(idParam);

            command.Connection.Open();
            command.ExecuteNonQuery();
            command.Connection.Close();
            count = (int)command.Parameters["@recordCount"].Value;
        }
        catch (Exception e)
        {
            throw new Exception("Error populating data", e);
        }
        finally
        {
            command.Connection.Close();
            command.Connection.Dispose();
        }

        return count;
    }

    protected static bool DeleteBO(ref SqlCommand command)
    {
        int result = 0;
        try
        {
            command.Connection.Open();
            result = command.ExecuteNonQuery();
        }
        catch (Exception e)
        {
            throw new Exception("Error deleting data", e);
        }
        finally
        {
            command.Connection.Close();
            command.Connection.Dispose();
        }

        return result > 0;
    }


    protected static int GetFKcount(ref SqlCommand command)
    {
        int count = 0;

        try
        {
            command.CommandType = CommandType.StoredProcedure;
            DbParameter idParam = command.CreateParameter();
            idParam.DbType = DbType.Int32;
            idParam.Direction = ParameterDirection.InputOutput;
            idParam.ParameterName = "@recordCount";
            idParam.Value = 0;
            command.Parameters.Add(idParam);

            command.Connection.Open();
            command.ExecuteNonQuery();
            command.Connection.Close();
            count = (int)command.Parameters["@recordCount"].Value;
        }
        catch (Exception e)
        {
            throw new Exception("Error populating data", e);
        }
        finally
        {
            command.Connection.Close();
            command.Connection.Dispose();
        }

        return count;
    }

    public static T GetById<T>(Guid Id)
        where T : BOBase
    {
        return GetById<T>(Id, null);
    }


    abstract public static T GetById<T>(Guid Id, List<string> propertyNamesToBypassInstantiation)
        where T : BOBase;

    public static EquatableList<T> GetByCriteria<T,TCriteria>(TCriteria myCriteria)
        where T : BOBase
        where TCriteria : BaseCriteria
    {
        return GetByCriteria<T, TCriteria>(myCriteria, null);
    }


    public static EquatableList<T> GetByCriteria<T, TCriteria>(TCriteria myCriteria, List<string> propertyNamesToBypassInstantiation)
        where T : BOBase
        where TCriteria : BaseCriteria
    {
        return GetByCriteria<T, TCriteria>(myCriteria, null, -1, -1, propertyNamesToBypassInstantiation);
    }

    public static EquatableList<T> GetByCriteria<T, TCriteria>(TCriteria myCriteria, string sortExpression, int startRowIndex, int maximumRows)
        where T : BOBase
        where TCriteria : BaseCriteria
    {
        return GetByCriteria<T, TCriteria>(myCriteria, sortExpression, startRowIndex, maximumRows, null);
    }

    abstract public static EquatableList<T> GetByCriteria<T, TCriteria>(TCriteria myCriteria, string sortExpression, int startRowIndex, int maximumRows, List<string> propertyNamesToBypassInstantiation)
        where T : BOBase
        where TCriteria : BaseCriteria;

    abstract public static int GetCountForCriteria<TCriteria>(TCriteria myCriteria)
        where TCriteria : BaseCriteria;

    abstract public static bool Save<T>(T myobject)
        where T : BOBase;


    abstract public static bool Delete<T>(Guid Id)
        where T : BOBase;


    abstract public static int GetFKcount<T>(Guid Id)
        where T : BOBase;

    abstract internal static void CreateCriteriaParameters<T, TCriteria>(ref SqlCommand myCommand, TCriteria myCriteria)
        where T : BOBase
        where TCriteria : BaseCriteria;
}

这是应该返回的最后一个底层类的部分代码:

public partial class PersonDB : DBBase
{

    public override static Person GetById(Guid Id, List<string> propertyNamesToBypassInstantiation)
    {
        SqlCommand command = GetDbSprocCommand("sprocPersonSelectSingleItem");
        command.Parameters.Add(CreateParameter("@id", Id));
        return GetSingleBO<Person>(ref command, propertyNamesToBypassInstantiation);
    }

    public override static EquatableList<Person> GetByCriteria(PersonCriteria myCriteria, string sortExpression, int startRowIndex, int maximumRows, List<string> propertyNamesToBypassInstantiation)
    {
        SqlCommand command = GetDbSprocCommand("sprocPersonSearchList");
        CreateCriteriaParameters(ref command, myCriteria);
        CreatePagingAndSortingParameters(ref command, sortExpression, startRowIndex, maximumRows);
        return GetBOEquatableList<Person>(ref command, propertyNamesToBypassInstantiation);
    }
}

4 回复 | 直到 16 年前

KeithS 16 年前

DBBase被定义为非泛型;这意味着您不能声明它的泛型实例。这是我看到的最大的编译时错误。

一般来说,换上这种型号是个坏主意,因为你想让这家工厂生产的每一种新型号都需要一个新的箱子。经过几十个新类型之后,这个switch语句将太长,无法有效地维护。为你的工厂试试这个:

public class DALFactory
{
   private Dictionary<Type, Func<DBBase>> factoryMethods;

   public void Register(Type type, Func<DBBase>> producer)
   {
      factoryMethods[type] = producer; //last-in wins
   }

   public DBBase GetObject(Type type)
   {
       if(factoryMethods.ContainsKey(type))
          return factoryMethods[type]();
       return null; //or throw exception
   }

   public Func<DBBase> GetFactoryMethod(Type type)
   {
       if(factoryMethods.ContainsKey(type))
          return factoryMethods[type];
       return null; //or throw exception
   }
}

...

var factory = new DALFactory();
factory.Register(typeof(PersonDB), ()=>new PersonDB());
//Register other named or anonymous factory methods that produce objects

在设置工厂时,可以注册任意多个工厂方法,而无需更改工厂本身。

Amanda Kitson 16 年前

尽管所有关于如何制造一个好的通用工厂的评论都很好,但这不是我的问题。我遇到的问题是,即使我的工厂返回对该类的引用,我也无法访问该类上的任何方法。

事实证明,如果你在一个类上有静态方法,当你有一个类的“实例”时,它们就不可用了。因为我在派生类中的所有方法都是静态的,所以我认为我实际上根本没有得到类的实例。原来我是。。。。

无论如何,因为我真正需要的是一种方法来获取对派生类中方法的引用,所以我找到了一个使用GetType、GetMethod和方法信息调用改为调用方法。

我最初尝试获取对派生类的引用的方法:

public static bobase GetByCriteria<T,TCriteria>(TCriteria myCriteria)
            where T : bobase
            where TCriteria : BaseCriteria
        {
            T myObject = default(T);
            Type[] myMethodTypes = new Type[]{typeof(string),typeof(int),typeof(TCriteria)};
            System.Reflection.MethodInfo myMethod = myObject.DBclass.GetMethod("GetByCriteria", System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Static, null, myMethodTypes, null);
            object[] myMethodParameters = new object[]{"someValueHere", 1, myObject};
            return (bobase)myMethod.Invoke(null, myMethodParameters);
        }

基本类:

public abstract class bobase
    {
        internal virtual Type DBclass
        {
            get
            {
                return Type.GetType(this.GetType().Name + "DB");
            }
        }
    }

我知道GetMethod使用反射来获取数据,因此可能会对性能造成某种影响。如果有更好的方法来获取对不使用反射的静态方法(比如静态方法工厂)的引用,我很想听听。

Sebastian Brózda 16 年前

我在我的项目中使用这样一个工厂:

public class SomeFactory
{
  private static SomeFactory instance = new SomeFactory();

  public static SomeFactory Instance
  {
      get
      {
          return instance;
      }
  }

  private static Dictionary<Type, Type> classes = new Dictionary<Type, Type>();

  static SomeFactory()
  {
      // add here classes that would be created by a factory
      classes.Add(typeof(IClass1), typeof(Class1));
      classes.Add(typeof(IClass2), typeof(Class2));
  }

  public T Create<T>()
  {
      return (T)System.Activator.CreateInstance(repos[typeof(T)]);
  }
}

使用

SomeFactory.Instance.Create<IClass1>()...

Mark 16 年前

为什么不使用属性并创建一个动态工厂呢

公共静态类MyFactory { private static Dictionary objects=new Dictionary();

    static MyFactory()
    {
        // Scan the assembly
        foreach (Type type in Assembly.GetExecutingAssembly().GetTypes())
        {
            MyAttribute[] frameAttributes =
                type.GetCustomAttributes(typeof (MyAttribute), false) as MyAttribute[];
            foreach (MyAttribute myAttribute in frameAttributes)
            {
                objects.Add(myAttribute.SomeKey, type);
            }
        }
    }