Question

目前我有一个继承结构，比如说Employee和Manager类，继承自Person抽象类我应该为每个具体类实现一个存储库，还是为整个继承结构实现一个存储库？就个人而言，我觉得每个具体类的一个存储库更正确以下是我对此方法的实现。我将Data Mapper模式与Repository一起使用但在实现这种方法时遇到了一些困难：我不知道除了Data Mapper类之外的哪些方法，但放在那里也很尴尬

public enum PersonType
{
    Unknown = 0,
    Employee = 1,
    Manager = 2
}

public abstract class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }    
    public PersonType Type { get; set; }

    //Omitted properties and methods
}

public class Employee : Person
{
    public string EmployeeNo { get; set; }

    //Omitted properties and methods
}

public class Manager : Person
{
    public string ManagerNo { get; set; }

    //Omitted properties and methods
}

以下是mappers类：

public interface IMapper
{
    bool CanMap(PersonType type);
    Person MapFrom(DataRow dataRow);

    //This method is awkward to put here
    SqlCommand CreateUpdateCommandFrom(Person person);  
}

public abstract class MapperBase : IMapper
{
    public abstract bool CanMap(PersonType type);
    public abstract Person MapFrom(DataRow dataRow);
    public abstract SqlCommand CreateUpdateCommandFrom(Person person);

    protected T MapCommonPropertiesFrom<T>(DataRow dataRow) where T : Person, new()
    {
        return new T
        {
            //Populate common properties like id, name, age
        };
    }
}

public class EmployeeMapper : MapperBase
{
    public override bool CanMap(PersonType type)
    {
        return type == PersonType.Employee;
    }

    public override Person MapFrom(DataRow dataRow)
    {
        Employee employee = MapCommonPropertiesFrom<Employee>(dataRow);
        //Populate employee properties
        return employee;
    }

    public override SqlCommand CreateUpdateCommandFrom(Person person)
    {
        SqlCommand updateCmd = new SqlCommand();
        //Set parameters for updateCmd from person properties
        return updateCmd;
    }
}

//Similar class for ManagerMapper

下面是一个用于查找mapper类的寄存器类

public static class MapperRegistry
{
    private static List<IMapper> _Mappers = RegisterMappers();

    private static List<IMapper> RegisterMappers()
    {
        return new List<IMapper>
        {
            new EmployeeMapper()
            //ManagerMapper
        };
    }

    public static IMapper FindMapperFor(PersonType type)
    {
        foreach (IMapper eachMapper in _Mappers)
        {
            if (eachMapper.CanMap(type))
            {
                return eachMapper;
            }
        }

        throw new ArgumentException(string.Format("Cannot find mapper for {0}", type));
    }
}

最后一个类是存储库类

public class PersonRepository
{   
    public Person FindBy(int id)
    {
        //Execute query command in db, get datatable back, store each person
        DataTable returnedData = ExecuteQueryCommand(id);
        PersonType type = int.Parse(returnedData.Rows[0], "Id");
        IMapper mapper = MapperRegistry.FindMapperFor(type);
        return mapper.MapFrom(returnedData.Rows[0]);
    }

    private DataTable ExecuteQueryCommand(int id)
    {
        //Execute query command in db
        return new DataTable();
    }

    public void Update<T>(T person) where T : Person
    {
        IMapper mapper = MapperRegistry.FindMapperFor(person.Type);
        SqlCommand updateCmd = mapper.CreateUpdateCommandFrom(person);
        //Execute update command
    }
}

我觉得不对的是CreateUpdateCommandFrom（），目前放在Mapper类中，右边应该放在respository类中，但在一般的仓库类中，我们不知道子类的特定属性，如EmployeeNo在Employee中在Manager类中的class和ManagerNo，因此我们无法在存储库中创建常见的SqlCommand

有没有更好的方法？非常感谢你

Answer 1

有没有更好的方法？非常感谢你

是的，有更好的方法。

当您使用SQL数据库时，请避免重新发明轮子并使用ORM工具，例如nHibernate或Entity Framework，最好使用LINQ支持。

存储库和继承

1 个答案: